Print

Physiol Rev
83: 1359 –1400, 2003; 10.1152/physrev.00007.2003.
Plasma Membrane Channels Formed by Connexins:
Their Regulation and Functions
JUAN C. SÁEZ, VIVIANA M. BERTHOUD, MARÍA C. BRAÑES, AGUSTÍN D. MARTÍNEZ,
AND ERIC C. BEYER
Departamento de Ciencias Fisiológicas, Pontificia Universidad Católica de Chile, Santiago, Chile;
and Department of Pediatrics, University of Chicago, Chicago, Illinois
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
I. General Comments
II. Background
A. Intercellular communication
B. Gap junction structure
III. Molecular Components of Gap Junctions
A. Gap junction proteins
B. The family of chordate gap junction protein subunits
C. Connexin genes
D. Transcriptional regulation and gene promoters
E. Posttranscriptional regulation of connexin mRNA levels
F. Connexin topology and secondary structure
IV. Biochemistry
A. Phosphorylation of connexins
B. Other protein modifications
C. Interaction and colocalization of connexins with other proteins
V. Formation and Degradation of Gap Junctions
A. Connexin biosynthesis and gap junction assembly
B. Gap junction and connexin degradation
VI. Hemichannels
A. Opening and closing hemichannels
B. Hemichannel functions
VII. Gap Junctions in Cardiovascular, Digestive, Reproductive, and Immune Systems
A. Cardiovascular system
B. Digestive system
C. Reproductive system
D. Immune system
VIII. Gap Junction Channels and Disease
A. Connexin mutations related to human peripheral neuropathy
B. Connexin mutations related to deafness and skin disorders
C. Connexin mutations related to human cataracts
IX. Phylogeny
X. Perspectives
1360
1360
1360
1360
1361
1361
1362
1362
1363
1364
1364
1366
1366
1368
1368
1368
1368
1370
1370
1370
1372
1373
1373
1375
1378
1379
1380
1380
1382
1382
1383
1383
Sáez, Juan C., Viviana M. Berthoud, Marı́a C. Brañes, Agustı́n D. Martı́nez, and Eric C. Beyer. Plasma
Membrane Channels Formed by Connexins: Their Regulation and Functions. Physiol Rev 83: 1359 –1400, 2003;
10.1152/physrev.00007.2003.—Members of the connexin gene family are integral membrane proteins that form
hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional
plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological
functions including paracrine intercellular signaling and in induction of cell death under pathological conditions.
Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction
channels are responsible for direct intercellular transfer of ions and small molecules including propagation of
inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic
responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and
connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or
www.prv.org
0031-9333/03 $15.00 Copyright © 2003 the American Physiological Society
1359
1360
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of
mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific
connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.
I. GENERAL COMMENTS
II. BACKGROUND
A. Intercellular Communication
The first indications that a pathway for direct cell-tocell communication might exist substantially preceded discovery of the gap junction structure. Weidmann (637), working with strips of myocardium, found that the space constant
for the spread of current extends beyond the expected value
for a single Purkinje fiber. He suggested that this phenomenon might be explained by the existence of a low-resistance
intercellular pathway. Stronger evidence supporting the existence of such a pathway was provided by the discovery of
electrical transmission at the giant crayfish motor synapses
(170). Later, this type of pathway was demonstrated in other
excitable tissues (22, 34, 162) and in nonexcitable cell types
(184, 356, 432, 468, 482). Today, it is accepted that cells of
Physiol Rev • VOL
B. Gap Junction Structure
Electron microscopy studies provided evidence for a
structure responsible for intercellular electrical transmission. Robertson (491) demonstrated the structural units
of the neuronal junction. In studies of excitable tissues, a
close apposition between the plasma membranes of adjacent cells was observed when current transfer occurred,
but it was absent when electrical transmission was not
detectable (22, 440, 482). This intercellular junction has
been given several names, including nexus, macula communicans, and gap junction. The designation “gap junction” from the work of Revel and Karnovsky (481) has
prevailed despite the contradiction between the function
and the morphological characteristics that it denotes.
The structure of gap junctions and their constituent
channels have been significantly elucidated. In transmission
electron micrographs of ultrathin tissue sections, gap junctions appear as regions where the plasma membranes of
adjacent cells closely approach each other, but appear to be
separated by a small gap of 2–3 nm (33, 481, 491) (Fig. 1A).
Electron micrographs of freeze-fracture replicas of vertebrate junctions show 8.5- to 9.5-nm particles on the P face
either free or in plaque-like arrays with complementary pits
on the E face (Fig. 1C). In many cases, these particles
(termed connexons) are regularly ordered in a hexagonal
pattern that has allowed detailed structural studies by other
techniques. Studies of gap junctions using atomic force microscopy (AFM) (226, 318) show a dense packing of particles with a center-to-center distance of 9–10 nm and a
similar long-range hexagonal packing. The particles contain
a porelike structure with a diameter of 2 nm, a depth of 1
nm, and a width of 3.8 nm based on freeze-fracture and AFM
analyses (226, 318, 481). X-ray diffraction examination of
isolated gap junction membranes (78, 362) and Fourier analysis of low-dose electron micrographs (595) show that each
particle or connexon within a gap junction forms a cylinder
with an apparent aqueous pore in the center. The wall of the
connexon is formed of six protein subunits (362). Other
studies suggest that these subunits may move with respect
to each other and control channel opening (594) (Fig. 3,
inset 1).
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
In this review, we provide a brief historical background
regarding gap junction structure and physiology and then
concentrate on reviewing several areas of active research in
the field of gap junctions including studies of the molecular
composition and biochemical regulation of these channels,
recent studies of hemichannels, and investigations of the
role of gap junction channels and hemichannels in various
normal physiological processes and diseases in vertebrates.
Due to limitations of space, some of the earlier investigations and some specific areas of gap junction biology that
have shown significant advance in recent years (e.g., nervous system) have not been considered in detail in the
current review. The reader is referred to previous reviews
for more detailed information on earlier studies (35, 48, 66,
67, 190, 539, 551). Several reviews have been published
recently on gap junction structure (534, 548, 665), trafficking
of protein subunits (154, 314, 317, 666), channel gating (36,
59, 108), pharmacological regulation (45, 499, 550), and functional features of the channels (353, 443, 540, 614). Other
reviews have covered the roles and regulation of gap junctions in development (338, 352) and in various mature tissues and organs, including vascular tissue (60, 91), urogenital smooth muscle (269), the heart (50) and cardiovascular
system (128), pancreas (377), endocrine glands (395), the
nervous system (65, 122, 123, 168, 546, 552), and the immune
system (11, 502, 503). Other reports describe the regulation
and role of gap junctions in tissue injury (120) and the
involvement of gap junctional communication in the phenotypes observed in connexin knock-out animals and/or different diseases (134, 540, 647, 662).
most invertebrate and vertebrate tissues can communicate
with their neighbors via a low-resistance intercellular pathway. In vertebrates, only a few cell types do not form gap
junctions in their fully differentiated state, including red
blood cells, spermatozoa, and skeletal muscle. Nevertheless,
the progenitors of these cells do express gap junctions (98,
386, 469, 495).
CONNEXIN CHANNELS
1361
The structure of the gap junction channel has been
refined in recent years (Fig. 1D). Using gap junctions
isolated from cells expressing a recombinant truncated
gap junction protein, Unger et al. (592) demonstrated the
dodecameric structure of the channel at a resolution of 7
Å in the membrane plane and 21 Å in the vertical direction; each hemichannel contains 24 ␣-helices corresponding to the four transmembrane domains of the six protein
subunits (592, 593). These structures were also suggested
by circular dichroism (77) and X-ray patterns obtained
from oriented gap junctions (577). The outer diameter of
the hemichannel is ⬃70 Å at the intracellular region and
⬃50 Å at the extracellular regions giving the complete
channel an hour glass-like appearance. The channel pore
narrows from ⬃40 Å diameter at the cytoplasmic side to
⬃15 Å at the extracellular side of the bilayer and then
widens to ⬃25 Å in the extracellular region (451, 592,
593). The connexon interfaces within a channel must be
tightly bound to form a tight seal. Thus the docking domain provides a high resistance to the leakage of current
carrying ions between the channel lumen and the extracellular space. Recently, conformational changes of the
Physiol Rev • VOL
cytoplasmic and extracellular surfaces in gap junction
plaques containing channels made of native connexin26, a
protein subunit, have been imaged using AFM (394). The
carboxy terminus reversibly collapses when increased
forces are applied to the AFM stylus. The presence of
Ca2⫹ in the buffer solution reduces the diameter of the
extracellular channel entrance from 1.5 to 0.6 nm, a conformational change fully reversible and specific among
the divalent cations. Calcium induces the formation of
microdomains, and the plaque height increases in 0.6 nm
(from 17.4 to 18 nm), indicating that Ca2⫹ induces conformational changes affecting the structure of connexin26
membrane channels (394).
III. MOLECULAR COMPONENTS
OF GAP JUNCTIONS
A. Gap Junction Proteins
Gap junction-enriched preparations, similar to those
utilized for structural studies, were used for biochemical
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
FIG. 1. Ultrastructure of gap junction plaques and channels. A: electron micrograph of a thin section of a rat liver
showing a long stretch of plasma membrane apposition corresponding to a gap junction between two hepatocytes
(arrows). Inset corresponds to a magnified view of a gap junction region showing the heptalaminar structure. B:
immunogold labeling of connexin (Cx) 43 in an annular gap junction from a rat Leydig cell. C: freeze-fracture view of a
gap junction plaque in rat hepatocytes; the protoplasmic (P) and exoplasmic (E) faces are indicated. D: dimensions of
gap junction channels estimated from X-ray diffraction studies. Magnification bar: 600 nm in A, inset; 200 nm in B; 0.1
nm in C. [Modified from Perkins et al. (451).]
1362
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
B. The Family of Chordate Gap Junction
Protein Subunits
The production of antibodies to the main protein in
isolated liver gap junction preparations, and the synthesis
of oligonucleotide probes based on the amino-terminal
sequence information, allowed the isolation of rat and
human cDNA clones encoding a liver gap junction protein
of 32 kDa (300, 442). Proof that this protein produces gap
junction channels came from its expression in Xenopus
oocytes (138, 566, 639). It became evident that there was
a family of subunit gap junction proteins when Beyer et al.
(52) isolated cDNA clones encoding a related, but clearly
different, polypeptide of 43 kDa corresponding to a rat
heart gap junction protein, which they named connexin43
(Cx43). While connexins were originally denoted according to the tissue of origin or the apparent size of a
polypeptide as determined by SDS-PAGE, it soon became
clear that such designations were inappropriate, because
many of these proteins are not uniquely expressed in a
single tissue (52), and their mobilities on SDS-PAGE may
vary with electrophoresis conditions (196). Therefore, to
distinguish members of this family, a standard nomenclature was needed. The most widely used system uses the
word connexin (often abbreviated Cx) followed by a suffix indicating the predicted molecular mass of the
polypeptide connexin (in kilodaltons) to distinguish different protein subunits (52, 53). In some cases, a prefix is
added to indicate the species of origin. The finding that
two (or more) connexins may have similar molecular
mass has led to the use of a decimal point to distinguish
them (e.g., mCx30.3 or mCx31.1). Some confusion has
also been created when orthologous and functionally homologous connexins have different molecular masses
Physiol Rev • VOL
(e.g., rat Cx46 vs. bovine Cx44 vs. chicken Cx56). An
alternative (but also problematic and less widely used)
nomenclature in which connexins are classified in subclasses according to amino acid sequence homology has
also been proposed (423, 486).
Subsequently, a number of cloning strategies including hybridization screening of genomic and cDNA libraries at reduced stringency and use of the polymerase chain
reaction with degenerate/consensus primers have been
successfully applied to identify additional members of the
connexin family (for recent review, see Ref. 653).
C. Connexin Genes
Recently, the screening of the mouse and human
genomic databases has revealed 19 and 20 connexin
genes in the mouse and human genome, respectively (55,
359, 417, 653). A dendrogram for all identified human
connexins is shown in Figure 2A. The genes for various
connexins have been localized to human (32, 92, 161, 214,
233, 271, 417, 654) and mouse (9, 93, 207, 215, 233, 521)
chromosomes. Connexin genes are found in many different chromosomes, but there is a cluster of connexins in a
region of mouse chromosome 4 (214) which is syntenic to
a region in human chromosome 1. The genes for many
connexins have been cloned, and the gene structure of
other connexins has been partially assessed by DNA blotting and by the polymerase chain reaction (for a review,
see Ref. 653). The available information indicates that
many connexin genes have a similar organization, and
virtually all have only single copies in the haploid genome
(653). The sequence similarities between connexins and
their similar gene structures suggest that they have arisen
by gene duplication. In humans, a Cx43 pseudogene has
been identified (163).
Most connexin genes have a first exon containing
only 5⬘-untranslated (UTR) sequences and a large second
exon containing the complete coding region as well as all
remaining untranslated sequences (Fig. 2B). Exceptions
to this gene structure are the Cx32, Cx36, and Cx45 genes.
The human (and rodent) Cx32 gene contains alternative
first exons (containing only 5⬘-UTR) whose use is tissue
specific (411, 545, 547); some bovine Cx32 transcripts
have three exons, two of which contain only 5⬘-UTR (135).
The Cx36 (and the Morone americana Cx34.7) gene contains two exons, both of which contain untranslated and
translated sequences. The coding region is interrupted by
an intron (32, 97, 422, 423, 544). The Cx45 gene contains
three exons; exons 1 and 2 contain only 5⬘-UTR and exon
3 contains the full coding region and 3⬘-UTR (19, 242); all
Cx45 transcripts examined contain exons 2 and 3, while
some also contain exon 1 (242).
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
identification of protein components; initially, it was
thought that all gap junctions contained the same protein.
Evidence for differences in gap junction proteins came
from the differing electrophoretic mobilities (21–70 kDa)
of bands detected by SDS-PAGE in gap junction-enriched
preparations from different tissues (211, 219, 285, 366). In
support of this, analysis of nonproteolized heart gap junctions by electron microscopy showed a fuzzy interface
that was absent in isolated liver gap junctions or proteolyzed heart gap junctions (365, 535). Comparison of heart
and liver gap junctional proteins by two-dimensional peptide mapping of proteolytic fragments followed by highpressure liquid chromatography revealed differences between these proteins (200). Furthermore, microsequencing of the amino-terminal regions of the hepatic and
cardiac proteins revealed both similarities and dissimilarities (414). Subsequently, sequencing of a lens gap junction protein showed that it differed from both the liver
and heart proteins (284).
CONNEXIN CHANNELS
D. Transcriptional Regulation and Gene Promoters
In various cell types, different treatments are known
to increase the levels of connexin mRNA due to enhanced
transcription. For example, cAMP induces elevation of
Physiol Rev • VOL
the Cx43 transcription rate in Morris hepatoma cells
(380). Moreover, the transcription rates of Cx32 and Cx26,
but not Cx43, are upregulated by glucocorticoids in liverderived cells (479), and the phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] induces transcriptional upregulation of Cx26 in human immortalized MCF-10 mammary epithelial cells (340). Also, the large increase of
Cx43 in myometrium before parturition is at least in part
due to increased transcription (433, 486). Thus knowledge
of connexin gene structure and identification of regulatory elements will allow us to understand the transcriptional regulation of connexin expression.
The basal promoter of the rat Cx32 gene was first
localized to a region ⫺179 to 0 or ⫺134 to 0, immediately
upstream of the first exon (17). The mouse Cx32 gene
contains two putative binding sites for the transcription
factor HNF-1 and consensus motifs for NF-1 as well as
NF␬B within the 680 bp upstream of the main transcription start site (215). Cx32 cDNA clones from rat or mouse
liver, sciatic nerve, and embryonic stem cells differ (545).
They correspond to different splicing variants with a different 5⬘-UTR or exon 1, each with its own promoter
region (545).
The human Cx32 gene can be transcribed from two
tissue-specific promoters, P1 and P2, leading to the production of two mRNAs with different 5⬘-UTRs through the
use of alternative exons (411). The P1 promoter is functional in liver and pancreas and is located more than 8 kb
upstream of the translation start codon, while the P2
promoter is functional in nerve cells and is located 497 bp
upstream from the translation start codon (411). Cx32
expression in vitro is strongly activated by direct binding
of SOX10, a common transcription factor for other myelin
genes (56). Methylation of the Cx32 (and Cx43) promoter
at Msp I/Hpa II restriction sites correlates well with cell
type-dependent decreased transcriptional activity (459).
Sequence analysis of mouse Cx37 gene has revealed
that the regions flanking exon I contain a consensus
“TATA box” 43 bp 5⬘ from the transcription start site
preceded by several putative transcription factor binding
sites and a 282-bp truncated L1Md transposon (529).
Determination of the structure and sequence of the
Cx43 gene and analysis of trans-activation have elucidated some of the hormonal and pharmacological regulation of Cx43 expression. Sullivan et al. (565) and Yu et al.
(674) cloned the mouse and rat Cx43 genes, identified the
transcriptional start site, and showed that there were a
number of putative transcription factor binding sites
within the 5⬘-flanking region including a TATA box, AP-1,
AP-2, Sp1, CRE sites, and half-palindromic estrogen response elements. The basal promoter is contained within
⬃110 bp 5⬘ to the start site (88). DNase I footprinting
assays have confirmed the use of AP-1 (⫺44 to ⫺36) and
Sp1 (⫺77 to ⫺69 and ⫺59 to ⫺48) consensus sequences;
moreover, mutation of this AP-1 site abolishes phorbol
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
FIG. 2. Phylogenetic tree and gene structure of connexins. A phylogenetic tree for the connexin family is shown in A. The tree was
constructed by aligning the protein sequences using CLUSTAL W and
the DRAWGRAM representation (http://workbench.sdsc.edu). Because
no sequence corresponding to human Cx33 has been deposited in the
databases, and it is not identifiable in available genomic sequence, all
sequences used for the aligment are from human origin with the exception of rat Cx33. (The accession numbers for the connexin sequences are
as follows: Cx25, AJ414563; Cx26, NM_004004; Cx30, AJ005585; Cx30.2,
AC004977; Cx30.3, BC034709; Cx31, NM_024009; Cx31.1, AF052693; Cx31.3,
AF503615; Cx31.9, AF514298 and NM_152219; Cx32, NM_000166; rat Cx33,
M76534; Cx36, NM_020660; Cx37, AF132674; Cx40, AF151979; Cx40.1,
AJ414564; Cx43, AF151980; Cx45, NM_005497; Cx46, AF075290; Cx46.6,
NM_020435; Cx50, AF217524; Cx59, AF179597; Cx62, NM_032602). A diagram of the structure of connexin genes is shown in B. B, top: most
connexin genes contain two exons and an intron of variable length; the first
exon contains only 5⬘-untranslated region (UTR) and the second exon
contains the full coding region and 3⬘-UTR. B, bottom: in some connexin
genes (e.g., Cx34.7, Cx36), the coding region is interrupted by an intron.
Untranslated and translated regions are depicted as boxes in dark gray and
light gray, respectively. The genomic DNA sequences not present in the
mRNA are represented by the black lines. Other exceptions to this gene
structure are described in the text.
1363
1364
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
consensus mammary gland factor binding site (276). The
region ⫺140 to ⫺113 of the Cx26 promoter includes an Sp
binding site overlapping with an AP-2 binding site which
are responsible for the upregulation of Cx26 in the myometrium during pregnancy and in the mammary gland
during lactation (590).
The Cx31 gene promoter region contains five putative binding sites for the GATA transcription factor, a
⌵F␬〉 element, a CAAT box, and E-box/E-box related
sequences (172). Interestingly, if part of the intron sequence is deleted, the promoter activity is lost (172).
E. Posttranscriptional Regulation of Connexin
mRNA Levels
The abundance of mRNA can be affected by conditions that increase or reduce its stability. The 5⬘-UTR of
the Cx43 mRNA contains a strong internal ribosome entry
site that confers increased transcription levels (518; for a
review, see Ref. 638).
Elevated cAMP concentrations increase the levels of
Cx32 mRNA in primary cultures of rat hepatocytes without detectable changes in the transcriptional rate, suggesting an enhanced Cx32 mRNA stability (505). Moreover, during liver regeneration, the reduction in Cx26 and
Cx32 mRNA occurs without changes in transcriptional
rate, suggesting a posttranscriptional mechanism (293). In
this system, the administration of cycloheximide, a protein synthesis inhibitor, completely inhibits the disappearance of Cx26 mRNA, but not of Cx32 mRNA, suggesting
the participation of protein factors in destabilization of
the Cx26 mRNA (293). The reduction in liver Cx32 steadystate mRNA levels induced by bacterial lipopolysaccharide appears to occur at the posttranscriptional level,
since the rate of degradation of this message is higher
than the rate of transcription of the gene (185).
F. Connexin Topology and Secondary Structure
The amino acid sequences derived from each cloned
cDNA have been used to predict the structure of connexins. Hydropathy plots of several connexins predict the
presence of four hydrophobic domains, with a carboxyterminal hydrophilic tail. In addition, three hydrophilic
domains separate the hydrophobic regions (52, 220, 442)
(Fig. 3, inset 2). The possible connexin membrane topologies derived from these data were tested by examining
the protease sensitivity of isolated liver and heart gap
junctions. Antisera raised against synthetic oligopeptides
representing various segments of Cx26, Cx32, and Cx43
were used to map the connexin topology. The amino
terminus, the carboxy terminus, and a loop in the middle
of the protein are all located on the cytoplasmic side of
the junctional membrane, and the predicted extracellular
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
ester-induced transactivation of Cx43 gene transcription
in uterine smooth muscle cells (178). Transfection studies
using Cx43 constructs linked to luciferase have shown the
responsiveness of Cx43 transcription to estrogen, parathyroid hormone, and prostaglandin (94, 674). cAMP,
which can also increase Cx43 expression (380), may serve
as the mediator of the parathyroid hormone and prostaglandin effects (519) through the Cx43 promoter cAMP
response elements (18). The mechanism of the estrogeninduced response is not so clear; Piersanti and Lye (460)
have suggested that it occurs indirectly through production of c-fos, which interacts with the AP-1 sites. Electrophoretic mobility shift assays have demonstrated c-jun
and Sp1 binding at the AP1 and Sp1 sites, respectively
(141). In positions ⫺480 and ⫺464 of the rat gene, there is
a thyroid hormone binding sequence that is able to activate the promoter (561).
Rat Cx43 and Cx30 transcription may be transactivated by the Wnt-1 signaling pathway, probably through
TCF/LEF binding elements (376, 600). These are HMG box
transcription factors that bind to ␤-catenin in response to
activation of the Wnt-1 signaling pathway, and not
through a cAMP-induced pathway (600). Functional analysis demonstrated that mouse Cx43 promoter constructs
could be activated in zebrafish embryonic neural crest
cells (87), suggesting that the sequence motifs and transcriptional regulation involved in targeting Cx43 expression to neural crest cells are evolutionarily conserved in
zebrafish and mouse embryos.
The Cx40 mRNA sequence is identical in all tissues
studied (198). Thus transcriptional regulation may account for the differences in levels of Cx40 transcripts
detected during development and among different tissues.
Transient transfection studies have demonstrated that the
basal promoter activity of the Cx40 gene lies within 300
bp upstream of the transcription start site and that a
strong negative regulatory element is present in the intron
in the region from ⫹100 to ⫹297 bp (530). Moreover,
potential transcription binding sites include AP-1, AP-2,
Sp1, TRE, p53, and a TATA box located near exon 1 (530).
Transcription of Cx40 is transactivated by Tbx5 (T-box
transcription factor 5) and the homeodomain transcription factor Nkx2–5 (62). Heterozygous and homozygous
Tbx5-deficient mice have similar features to the human
Holt-Oram syndrome (62), and it has been suggested that
decreased Cx40 transcription may contribute to the cardiac conduction defects observed in this syndrome.
The mouse Cx26 promoter contains at least two transcription start sites and is located in a very GC-rich region
without a TATA box, reminiscent of promoters of housekeeping genes (215). Consensus sequences for a metal
response element, NF␬B, and six GC boxes were found
within 600 bp upstream of the Cx26 transcription start
sites in mouse and human DNA (215, 276). Moreover, the
human sequence contains a YY1-like binding site and a
CONNEXIN CHANNELS
1365
connexin domains can be detected on the extracellular
surfaces of the junctional membranes (218, 382, 471, 663,
679, 682) (Fig. 3, inset 2). The four transmembrane spanning regions and the extracellular loops contain many
identical residues or conservative substitutions among
the different connexins. In contrast, the cytoplasmic domains are unique to each connexin; the cytoplasmic loop
and the carboxy terminus vary extensively in length and
amino acid composition.
Sequence analysis and expression of wild-type or
mutant connexins are approaches that are actively being
used to determine residues within these sequences that
may be responsible for various channel properties. The
transmembrane regions must be responsible for spanning
the plasma membrane and forming the aqueous pore.
Three transmembrane regions M1, M2, and M4 contain
Physiol Rev • VOL
mainly hydrophobic amino acid residues, while M3 also
contains a number of charged (positive and negative)
amino acid residues. Therefore, M3 has been modeled as
an amphipathic ␣-helix, and it has been suggested that its
hydrophilic face might line the pore of the gap junction
channel (35). Structural studies (593) indicate that regions of two ␣-helices line the inner wall of the channel.
Scanning cysteine mutagenesis of Cx46 hemichannels in
which amino acid residues from M1 and M3 were replaced
by cysteines indicated that both transmembrane regions
contribute to the lining of the pore (681). Scanning cysteine mutagenesis of Cx32 channels suggests that M2 also
contributes to the lining of the pore (543).
The extracellular regions must be responsible for the
“docking” of connexons which occurs by collision of two
connexons, each provided by each of two adjacent cells.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
FIG. 3. Diagram illustrating the pathways from transcription to degradation of connexins. Nascent connexin mRNAs
leave the nucleus and are translated in the rough endoplasmic reticulum (ER). A newly synthesized connexin (Cx) is
folded and then assembled with other connexins into hemichannels. While most Cx26 and only some Cx43 hemichannels
are inserted directly into the plasma membrane, most hemichannels made of other connexins, including Cx43 and to a
minor extent Cx26, follow the exocytic/secretory pathway [i.e., they go through the Golgi apparatus (GA) and are
transported in vesicles to the plasma membrane along microtubules]. Hemichannels can stay free on the cell surface or
they can dock with an hemichannel at sites of cell-cell contact to form a gap junction channel. Gap junction (GJ)
channels may cluster to form a GJ plaque. 1: Hemichannels are at a steady-state between two conformational states
(open and closed). 2: Connexin topology at the plasma membrane. 3: En face view of a growing GJ plaque. Gap junction
channels or hemichannels may be ubiquitinated (Ub). Internalization of a gap junctional plaque with formation of an
annular ring is depicted on the cell on the left; this ring interacts with actin filaments and moves toward lysosomes and
proteasomes where its protein components are degraded. Misfolded connexins or ubiquitinated hemichannels that might
be degraded by the proteasome are shown on the top right corner on the cell on the right.
1366
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
IV. BIOCHEMISTRY
A. Phosphorylation of Connexins
All studied connexins with the exception of Cx26
(508, 585) are phosphoproteins (for previous reviews, see
Refs. 100, 322, 506). Connexin phosphorylation has been
implicated in the regulation of intercellular communication through a number of mechanisms, including connexin biosynthesis, trafficking, assembly, membrane insertion, channel gating, internalization, and degradation
(16, 42, 44, 146, 217, 229, 320, 330, 390, 401, 426, 470, 567,
586, 670, 669). It is likely that some connexin phosphorylation occurs before insertion into the plasma memPhysiol Rev • VOL
brane, but some must occur at the plasma membrane to
affect gating. Nevertheless, the specific phosphorylation
sites and functional role for most of them have not been
elucidated.
The most extensively studied connexin in terms of
modification by protein kinases and phosphatases is
Cx43. This protein contains several consensus sites for
phosphorylation in the carboxy terminus, several of
which have been identified as target sites for specific
protein kinases. Fusion proteins containing the cytoplasmic tail of Cx43 or synthetic peptides corresponding to
the deduced sequences in this region are phosphorylated
by protein kinase C (PKC), mitogen-activated protein kinase (MAPK), and cdc2 kinase (323, 507, 575, 634). The
identified phosphorylation sites are Ser-368 and Ser-372
phosphorylated by PKC (507) and Ser-255, Ser-279, and
Ser-282 phosphorylated by MAPK (633, 634). Although
phosphorylated Cx43 can be found at the plasma membrane (400), phosphorylation of Cx43 could also happen
in intracellular compartments (103, 315).
Epidermal growth factor (EGF)-, vascular endothelial growth factor (VEGF)-, fibroblast growth factor 2
(FGF-2)-, and platelet-derived growth factor (PDGF)-induced Cx43 phosphorylation can be mediated by intracellular kinase pathways that activate MAPK also termed
ERK1/2 (132, 229, 230, 263, 564, 664) (Fig. 4). In some
systems, this effect appears to occur in a PKC-independent manner (449), but in other systems it can be prevented by PKC inhibition, but not by inhibition of the
ERK1/2 pathway (133). In T51B cells, this effect requires
the activation of both PKC and ERK1/2 (229). MAPK
activation may also mediate the induction of Cx43 phosphorylation by lysophosphatidic acid (LPA) (221). The
observations are consistent with the variations in crosstalk between different protein kinase-dependent pathways in different cell types (e.g., differences in the relative activity of each pathway and different subcellular
compartmentalization of different protein kinases). It has
been confirmed that Cx43 is a MAPK substrate in vivo and
that phosphorylation on Ser-255, Ser-279, and/or Ser-282
is sufficient to disrupt gap junctional intercellular communication (634). Accordingly, 3T3 A31 fibroblasts transfected with a carboxy-terminal truncated Cx43 remain
highly coupled after treatment with PDGF (388). Nevertheless, other studies suggest that other unknown factors
besides phosphorylation are required for disruption of
Cx43-mediated cell-to-cell communication (231, 232). The
consensus sites for MAPK and cdc-2 kinase present in
Cx43 are apparently shared, since the two-dimensional
tryptic maps of the carboxy terminus phosphorylated
by MAPK or cdc-2 kinase appear identical (507). Yet,
comparison of two-dimensional phosphotryptic peptide
analysis of the p34(cdc2)/cyclin B kinase-phosphorylated
carboxy terminus and of the P3 phosphoform of Cx43
immunoprecipitated from mitotic cells reveals several
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
This process apparently occurs through noncovalent
forces (180). White and co-workers (643, 648) demonstrated the importance of the second extracellular loop
(E2) in determining which connexins can interact to form
heterotypic channels. Synthetic peptides homologous to
the extracellular loop 2 of Cx40 or Cx43 selectively block
the function of the corresponding connexin (304). Werner
et al. (640) showed that site-directed mutagenesis of
amino acid residues within the extracellular loops that
differ among connexins alter but do not prevent gap
junctional communication. Biochemical studies have
shown that cysteines in the extracellular loops participate
in forming intramolecular but not intermolecular disulfide
bonds (252, 475). Mutation of any of these cysteines to
serines prevents gap junction channel formation (109,
110), emphasizing the importance of the secondary and
tertiary structures imposed on the connexins by the disulfide bonds. Alteration of the position of the cysteines in
Cx32 can seriously impair the ability to form functional
channels (165); these data have been used to model this
region as adopting a ␤-sheet conformation. The cysteine
residues involved in formation of the intramolecular disulfide bonds in Cx43 have been studied using site-directed mutagenesis (580); however, these differ from
those proposed for Cx32 (165). In expression systems,
different connexins form channels with differing properties including unitary conductance, selectivity/permeability, and gating/regulation (23, 73, 142, 144, 162, 292, 367,
389, 391, 617– 620). Some of the unique properties must be
conferred by the unique portions of the connexin sequences (many of which are located within or near the
cytoplasm). The main differences in the primary sequence
between two closely related connexins, Cx26 and Cx30,
are located in the cytoplasmic loop and carboxy-terminal
domains. Exchange of one or both of these domains has
demonstrated that the cytoplasmic domains interfere directly or indirectly with the permeability, conductance,
and voltage gating of the channels in HeLa cells transfected with Cx26/30 chimeras (367).
CONNEXIN CHANNELS
Physiol Rev • VOL
EGF receptor or Ca2⫹/calmodulin-dependent protein kinase have not been reported.
The stoichiometry of Cx32 phosphorylation in vitro
by PKC or cAMP-dPK is between 0.1 and 1 mol phosphate/
mol Cx32 (508, 511, 570), suggesting that not every channel or not every subunit within a channel is phosphorylated. The stoichiometry of in vivo phosphorylation and
identification of the cell compartment(s) in which Cx32
phosphorylation occurs have not been reported. Cx32 is
phosphorylated in Ser-233 by both cAMP-dPK and PKC
(508). It is likely that PKC phosphorylates other amino
acid residues that are not phosphorylated by cAMP-dPK
(570). Increased incorporation of 32P into Cx32 is observed when isolated liver gap junctions (previously phosphorylated by cAMP-dPK) are incubated with PKC (570);
moreover, two-dimensional tryptic phosphopeptide maps
of Cx32 immunoprecipitated from hepatocytes treated
with PKC activators show a higher number of 32P-labeled
peptides than the maps of Cx32 obtained from cells
treated with cAMP-dPK activators (508). Phosphorylation
of Ser-233 is not required for formation of functional
channels (640), but its possible role in other functions has
not been studied. The tyrosine residues phosphorylated
after activation of EGF receptor (130) have not been
identified.
Lens connexins are phosphoproteins, and changes in
their state of phosphorylation correlate with changes in
cell-cell communication (39, 248, 514, 670). In ovine lens,
Cx49 is phosphorylated by casein kinase I (89), and inhibition of casein kinase I increases intercellular communication between cultured lens cells (90). Moreover, Cx45.6
is phosphorylated at Ser-363 by casein kinase II; this
phosphorylation inhibits the cleavage of the connexin
carboxy terminus mediated by caspase-3-like protease
(669). Cx46 is phosphorylated in serine and threonine by
PKC in the lens cortex (514). Two phosphorylation sites
have been identified in Cx56, Ser-118 and Ser-493. These
sites are phosphorylated under basal conditions in lentoid-containing cultures. Upon activation of PKC, phosphorylation is enhanced in Ser-118 (39). Phosphorylation
of Ser-118 correlates with a reduction in intercellular
communication (39). The Cx56 phosphorylation and reduced intercellular communication induced by a tumor
promoter phorbol ester appear to be mediated by PKC-␥
(44).
Phosphorylation of other connexins (e.g., Cx31,
Cx37, Cx40, and Cx45) in transfected cells has been demonstrated directly by incorporation of 32P into the protein
or shift in their electrophoretic mobilities after treatments
that increase protein kinase activity (313, 328, 583, 584,
610, 613). Mouse and human Cx37 expressed in cell lines
are phosphorylated mainly in serine residues (328, 584).
Mouse Cx45 is detected as a doublet that is reduced to a
single 46-kDa band after treatment with alkaline phosphatase (613). After mutation or deletion of nine serine resi-
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
differences. This suggests that in vivo Cx43 phosphorylation would involve the participation of other protein kinase(s), which may be activated by the p34(cdc2)/cyclin B
kinase (321).
Numerous reports have described changes in the
state of phosphorylation of Cx43 through PKC-dependent
pathways. The pattern of Cx43 phosphorylation and the
functional consequences are cell type dependent (for reviews, see Refs. 322, 506). Ser-368 in Cx43 appears to be
an important site that may underlie the cellular uncoupling that follows TPA treatment, since mutation of Ser368 partially prevents this effect (323, 349).
The products of various oncogenes are tyrosine kinases that disrupt gap junctional communication by phosphorylation of tyrosine residues in Cx43. Oncogene products with tyrosine kinase activity phosphorylate Cx43 in
vivo (102, 160, 302) and in vitro (357). Similarly, c-Src
seems to be involved in loss of gap junctional communication induced when ligands bind to c-Src-associated receptors (466). The interaction with v-Src is mediated by a
proline-rich motif of Cx43, Pro-274-Pro-284 (264). Moreover, in vitro studies indicate that Cx43 is a substrate for
v-Src tyrosine kinase and that phosphorylation of Cx43
occurs in Tyr-247 and Tyr-265 (345). Expression in Cx43null cells of Cx43 constructs in which Tyr-247 and/or
Tyr-265 were replaced with phenylalanines suggests that
phosphorylation of both tyrosine residues is required for
the complete v-Src-induced disruption of gap junction
channel communication (345).
In rat (but not human) Cx43, Ser-257 is flanked by a
proline and a lysine, making it a possible site for phosphorylation by cGMP-dependent protein kinase. Accordingly, the extent of phosphorylation of rat Cx43, but not of
human Cx43, expressed in SkHep1 cells is increased by
8-bromo-cGMP (306).
Some studies have shown that activation of cAMPdependent protein kinase (cAMP-dPK) leads to a rapid
augmentation in Cx43 phosphorylation as detected by
immunoblotting (193) and increased intercellular communication (69, 186). However, direct phosphorylation of
Cx43 by cAMP-dPK has not been documented. The
polypeptides corresponding to the carboxy terminus of
Cx43 are not phosphorylated by cAMP-dPK (509, 575).
Moreover, activation of cAMP-dPK does not change the
32
P incorporation into Cx43 transfected into fibroblasts
derived from Cx43-null mice (575).
Cx32 is phosphorylated by cAMP-dPK, PKC, Ca2⫹/
calmodulin-dependent kinase II, and EGF receptor (130,
508, 511, 569, 570, 586). In rat hepatocytes, the effect of
cAMP-dPK is temporally correlated with increased junctional conductance (511). Similarly, in the human colonic
cell line T84, a rapid (⬍20 min) increase in intercellular
communication mediated by Cx32 gap junctions is induced by an increase in intracellular cAMP concentration
(84). Functional correlates of Cx32 phosphorylation by
1367
1368
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
B. Other Protein Modifications
The amino termini of several connexins contain potential consensus N-glycosylation sites, but they are not
utilized (474, 630), presumably because they are located
in the cytoplasm and therefore are not accessible to the
glycosylating enzymes. Fatty acylation of connexins has
been suggested by metabolic labeling studies (585), but
in-depth studies have not been published.
Modification of Cx43 by ubiquitination has been demonstrated (309, 312, 501) (Fig. 3). The residue to which
ubiquitin molecules are added has not been identified, but
it is likely to be a lysine.
Cleavage of the carboxy terminus of lens fiber-specific connexins has been proposed to occur naturally
during maturation of lens fiber cells (283). Studies of the
ovine Cx50 have identified calpain as the enzyme that
removes a 32-kDa portion of the carboxy tail of Cx50 (344,
669, 670). However, a similar phenomenon may not occur
in chicken lenses, since cleavage of Cx56 was not observed when lens cortex and lens nucleus homogenates
were prepared using EDTA (40).
C. Interaction and Colocalization of Connexins
With Other Proteins
Connexins may interact with other proteins within
the cell. Because gap junction isolation methods involve
the use of relatively harsh detergents, interacting proteins
do not copurify with connexins. However, other strategies have suggested some possible associated proteins.
Blotting experiments have suggested Cx32 could bind
calmodulin (604, 682). In addition, Cx43 contains SH2
domains that may be important for its interaction with
tyrosine kinases such as pp60v-src (264, 358). Recent studies have suggested an association of Cx43, Cx45, Cx46,
and Cx31.9 with the peripheral membrane protein ZO-1
(181, 310, 416, 417, 581) (Fig. 3), which was originally
Physiol Rev • VOL
identified as a component of tight junctions. Binding of
Cx32, but not Cx26, to another tight junction protein,
occludin, has also been demonstrated by coimmunoprecipitation experiments (288, 289). The expression of
Cx32, but not Cx32 truncated at position 220, wild-type
Cx26, or Cx43, in Cx32-null hepatocytes enhances the
expression of the tight junction proteins claudin, occludin, and ZO-1, which colocalize with Cx32, suggesting that
the Cx32-mediated intercellular communication participates in the formation of tight junctions (290). With the
use of a yeast two-hybrid protein interaction screen, the
interaction of Cx43 through its carboxy terminus with the
second PDZ domain of the ZO-1 protein has been demonstrated (181). The v-Src-induced disruption of gap junction plaques may occur through interaction of v-Src with
ZO-1 (579).
Connexins appear to interact with caveolin-1, a structural protein of lipid raft domains (112, 520); this interaction seems to be cell type specific, and its functional
significance is unknown. Colocalization of connexins with
other membrane proteins, including FGF receptors (268),
aquaporins (476), or cytoplasmic proteins such as calmodulin (549) and cytoskeletal proteins (182) has been
demonstrated.
V. FORMATION AND DEGRADATION
OF GAP JUNCTIONS
A. Connexin Biosynthesis and Gap
Junction Assembly
The development of specific anti-connexin antibodies has made possible in vitro studies of connexin biosynthesis by metabolic labeling and immunoprecipitation (reviewed in Refs. 314, 317). The biosynthetic studies have
been most extensive for Cx43. Pulse-chase studies show
that Cx43 is initially synthesized as a 40- to 42-kDa
polypeptide that is subsequently posttranslationally modified to forms with slightly slower mobilities on SDSPAGE due to phosphorylation of serine residues (102, 160,
399, 400). Multiple phosphates are added to Cx43, and at
least some of this phosphorylation occurs in a serine-rich
sequence near the carboxy terminus. Phosphorylation of
Cx43 to yield a phosphoform (P1) occurs soon after translation. Inhibition of protein trafficking with monensin or
brefeldin A reveals that partial phosphorylation of Cx43
occurs before its exit from the Golgi apparatus (315, 470).
The location at which connexins oligomerize into
connexons is connexin-type dependent (116, 129, 370,
402, 474); as examples, it appears that Cx32 assembles in
the endoplasmic reticulum (ER) (or ER/Golgi intermediate compartment) while Cx43 assembles in the transGolgi network (116, 129, 370, 402, 474). With the use of an
in vitro cell-free transcription/translation system, it has
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
dues in the carboxy terminus of Cx45, phosphorylation is
decreased by 90%, indicating that those serine residues
represent main phosphorylation sites in the protein (217).
Activation of cAMP-dPK leads to an electrophoretic mobility shift of human Cx40 that correlates with increased
cell-to-cell communication (610). However, the identification of amino acid residues with functional significance
and dissection of protein kinases responsible for their
phosphorylation await further studies.
Finally, treatment of some cells with phosphatase
inhibitors leads to increased Cx43 phosphorylation, suggesting the involvement of phosphoprotein phosphatases
2A and 2B (42, 104, 342). The phosphatases that mediate
dephosphorylation of other connexins have not been reported.
CONNEXIN CHANNELS
Physiol Rev • VOL
(401). However, some studies suggest that phosphorylation may not be an absolute requirement for assembly or
insertion of connexins into the plasma membrane. In
exogenous expression systems, Cx26, a nonphosphorylated protein, is able to induce junctional currents (23).
Moreover, truncated Cx43 or Cx32 constructs devoid of
some phosphorylatable serine residues from their carboxy termini can still induce intercellular coupling (162,
351, 640). In addition, phosphorylation of Cx43 can occur
in Madin-Darby canine kidney cells in the absence of
Ca2⫹-dependent cell adhesion molecule activity and does
not correlate with existence of intercellular coupling (42).
Formation of gap junction plaques requires clustering of gap junction channels. Increased levels of cAMP
induce clustering of Cx43 gap junction channels and enhanced gap junction plaque growth through a mechanism
that seems to be cell type dependent. In some cell types,
this process depends on polymerized actin while in others
it depends on intact microtubules and trafficking through
intracellular membrane compartments (158, 256, 445,
631). It has recently been suggested that the carboxy
terminus of Cx43 (including Ser-364) plays a role in the
cAMP-induced clustering of gap junction channels (575).
The differences observed between cell types might reflect
differences in the source from which additional connexons come (i.e., a pool at or near the plasma membrane or
a pool at earlier locations within the biosynthetic/exocytic pathway).
Connexins that are coexpressed in the same cell can
localize to the same gap junction plaque (404, 413, 428,
585, 115, 228, 660, 668) or to distinct membrane domains
(203, 553), suggesting the presence of a sequence motif in
connexins that determines its topographic fate. Although
differences in primary sequence between connexins
might explain the delivery of hemichannels to specific
plasma membrane domains, these sequences have not
been identified for most connexins. It has been reported
that the transmembrane domains, but none of the cytoplasmic domains, are required for the delivery of Cx32 to
its specific destination in cultured epithelial cells (337).
How gap junction channels aggregate and form small
junctional plaques is not yet resolved. In ultrastructural
studies, small particle aggregates have been found within
particle poor, flattened regions of the plasma membrane
as junctions are beginning to form between reaggregated
cells (255). Growth of gap junctions occurs by incorporation of additional gap junction channels to the plasma
membrane followed by their incorporation to the periphery of existing gap junction plaques (174, 331). Imaging of
living cells transfected with fluorescent protein-tagged
connexins suggests that connexins are delivered to the
gap junction plaque in cytoplasmic vesicles (260) that
move along microtubules (331). Large junctional plaques
can form by coalescence of small junctional plaques (227,
282).
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
been demonstrated that Cx26 hemichannels are integrated directly into plasma membranes in a posttranslational manner (5). In cells expressing two connexins, it is
possible to find hemichannels formed by both connexins
(heteromeric) (43, 246, 355, 372, 556) or hemichannels
constituted by one or the other protein (homomeric). In
studies performed in liver, oligomeric intermediates of
Cx26 are detected in an ER/Golgi intermediate compartment while oligomers containing both Cx26 and Cx32 are
preferentially detected in a Golgi membrane fraction
(129). This might have implications for the formation of
heteromeric connexons (see below). Newly synthesized
connexins appear to be transported to the plasma membrane through two different pathways: one sensitive to
brefeldin A (a drug that disrupts the Golgi compartment)
and one sensitive to nocodazole (a drug that disassembles
microtubules) (179, 370).
Connexons are inserted into the plasma membrane in
a closed configuration (Fig. 3, inset 1) perhaps at regions
of cadherin/catenin-mediated cell adhesion or near tight
junctions (169). Formation of gap junctions requires appropriate cell adhesion, especially that mediated by Ca2⫹dependent molecules (cadherins) (258, 400). Musil et al.
(400) have demonstrated that Cx43 localizes intracellularly and not at gap junctional plaques in the noncommunicating cell lines L929 and S180. The Cx43 in these cells
is incompletely phosphorylated. However, transfection of
the S180 cells with the cell adhesion molecule LCAM
(E-cadherin) restores gap junctional communication,
phosphorylation of Cx43 (to a “P2” form), and presence of
gap junction plaques. These findings suggest a relation
between the ability of cells to more extensively phosphorylate Cx43 and the ability to form communicating junctions. They also suggest a hierarchy of events in the
formation of intercellular junctions: a cell adhesion event
is required before formation of gap junction plaques. Similar observations regarding the requirement of cadherinmediated cell adhesion for development of gap junctions
have been made in epidermal cells (258). Cell-to-cell contact sites mediated by the cadherin-catenin complex also
seem to act as foci for gap junction formation as shown by
colocalization of connexins with E-cadherin or ␤-catenin
during gap junction formation in regenerating liver (169).
Moreover, antibodies to A-CAM (N-cadherin) or peptides
representing extracellular domains of Cx43 inhibit gap
junction formation in Novikoff hepatoma cells (381).
However, the effects of increased cell adhesion seem to
be cell type specific, since expression of exogenous cadherin decreased gap junctional communication between
mouse L cells but increased it in Morris hepatoma cells
(632). A role for Ca2⫹-independent cell adhesion molecules (e.g., N-CAM) has also been suggested (270).
Incorporation of connexons made of Cx43 into gap
junction plaques correlates with resistance to solubilization in Triton X-100 and with additional phosphorylation
1369
1370
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Some incompletely resolved issues are as follows:
how connexins are brought together to assemble into
connexons, how these connexons are incorporated into
the plasma membrane, how gap junctional channels become part of a plaque, and which other proteins/factors
participate in these processes. It is possible that no other
factors are necessary for channel or plaque formation
because purified connexons tend to aggregate in filaments
and sheets (557).
B. Gap Junction and Connexin Degradation
Physiol Rev • VOL
VI. HEMICHANNELS
Although for several decades hemichannels found at
nonjunctional membranes were thought to remain permanently closed to avoid cell death, data reported during
the last decade have documented the existence of regulatable hemichannel opening in cultured cells. Nevertheless, it is still not completely known whether cell surface
hemichannels have different permeability properties than
gap junction channels formed by the same connexin type.
Moreover, it is unknown whether physiological stimuli
may induce brief hemichannel openings that allow transfer of small molecules between the intracellular and extracellular compartments.
A. Opening and Closing Hemichannels
The opening of connexin hemichannels was first described based on the swelling and death of Xenopus oo-
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
Proteins in gap junctions are apparently rather shortlived. Based on in vivo labeling, Fallon and Goodenough
(157) estimated that the half-life of a major polypeptide in
liver gap junctions was in the range of 5 h. Similarly,
pulse-chase experiments have shown that connexins have
half-lives of 1–3 h in cultured cells (102, 115, 316, 586). A
similar half-life has been measured for Cx43 in intact lens
and heart (29, 399). However, at least some of the lens
fiber connexins are more stable, with half-lives of 2–3
days or more (38, 247).
Morphological and biochemical approaches have recently been applied to begin to elucidate the mechanisms
of gap junction degradation (reviewed in Ref. 49). Electron microscopy studies have implied endosomal internalization of entire junctions forming “annular gap junctions”
(Figs. 1B and 3) followed by degradation in lysosomal,
multivesicular body, or autophagosomal compartments
(260, 325, 326, 375, 397, 408, 447, 489, 533, 616). In vivo,
these structures have been most frequently found following pathological insults such as ischemia or during tissue
remodeling. Cell fractionation and immunoelectron microscopy studies have shown an association between
connexins and lysosomes in some cultured cells (515,
616). Murray et al. (398) found that in SW-13 adrenal
cortical tumor cells, many of the cytoplasmic annular
Cx43 gap junction profiles are associated with myosin II,
but not with tubulin, or vimentin-containing fibers. Disruption of microfilaments resulted in a decrease in the
number and an increase in the size of these annular gap
junctions, suggesting a role for myosin-containing cytoskeletal elements in annular gap junction turnover (327,
398). A recombinant Cx43 containing tetracysteine tags
was recently used to demonstrate that older Cx43 is removed from the center of plaques into pleiomorphic vesicles of widely varying sizes (174).
Recently, investigators have used biochemical or immunochemical techniques to study proteolysis of the subunit
gap junction proteins. Studies of Cx43 proteolysis in E36
Chinese hamster ovary cells have shown the major involvement of the ubiquitin-proteasome pathway in Cx43 degradation. In these cells, treatment with the protease inhibitor
N-acetyl-leucyl-leucyl-norleucinal (ALLN) induces accumu-
lation of Cx43 and a significant prolongation of its half-life.
Also, Cx43 degradation is abolished when ts20 Chinese hamster ovary cells, which contain a thermolabile ubiquitin activating enzyme, E1, are incubated at the restrictive temperature (309). Immunofluorescence studies in both primary
cultures of cardiac myocytes and in established cell lines
have shown that Cx43 gap junction plaques as well as the
Cx43 polypeptide exhibit rapid turnover rates. The rapid
disappearance of Cx43 staining can be blocked by inhibitors
of either the proteasome or the lysosome, implicating both
proteolytic systems in gap junction degradation (260, 311,
312). These studies have also shown that connexin degradation could be stimulated by cellular stress such as heat
shock (311). It is possible that the proteasome is mainly
involved in degradation of misfolded connexins (as occurs
for many other proteins); this process is called ER-associated degradation and serves as a quality control check point.
Misfolded connexins likely are dislocated from the ER and
then degraded by the proteasome. The involvement of this
pathway during connexin biosynthesis has been recently
demonstrated for wild-type Cx43 (612). The participation of
both proteasomal and lysosomal pathways in the degradation of Cx43 in the heart has also been demonstrated (29).
The published studies suggest that the preference of
one degradative pathway over the other is cell type dependent and that within the same cell type the degradative pathway chosen might depend on the metabolic/
pathological state of the cell. The experiments do not
allow differentiation between the possibilities of a sequential (e.g., the carboxy tail of Cx43 is degraded in the
proteasome while the core of the protein embedded in the
membrane is degraded by the lysosome) or parallel (Cx43
can be degraded by the proteasome or the lysosome)
pathway for degradation of connexins.
CONNEXIN CHANNELS
Physiol Rev • VOL
fiber hemichannels closed to maintain the high input resistance of lens cells.
Opening of Cx43 hemichannels induced by low extracellular [Ca2⫹] can be blocked by activation of a PKCdependent pathway (341, 350), suggesting the involvement of protein phosphorylation as a gating mechanism
that maintains the hemichannels closed. Likewise, the
membrane current mediated by Cx46 hemichannels expressed in Xenopus oocytes is greatly reduced by activation of a PKC-dependent mechanism (245, 412). Moreover, Cx43 is a substrate for MAPK (633). MAPK can be
activated by tyrosine kinase receptors, such as the EGF
receptor, or through transduction pathways that activate
PKC leading to direct or indirect phosphorylation of Cx43
via PKC or MAPK as proposed for Cx43 forming gap
junction channels (Fig. 4). A similar mechanism might
operate on Cx43 hemichannels. In support of this hypothesis, it is known that hemichannels of MAPK-phosphorylated Cx43 reconstituted in lipid vesicles remain preferentially closed, but dephosphorylated Cx43 forms opening hemichannels (280). Nevertheless, it is difficult to
conceive that under resting conditions MAPK would keep
the hemichannels closed without affecting gap junctional
communication. Alternatively, Cx43 forming hemichannels could be phosphorylated by a protein kinase activity
with several isoenzymes that show cellular compartmentalization (e.g., PKC). Fibroblasts from Cx43-null mice
transfected with Cx43 mutated at Ser-368, a change that
confers resistance to PKC-induced closure of gap junction
channels (323), show a decrease in hemichannel opening
after treatment with a phorbol ester to activate PKC (349).
Closure of hemichannels has been observed after
extracellular application of lanthanide cations, La3⫹ (99,
251, 280, 291), or Gd3⫹ (562), or treatment with gap
junction channel blockers, such as octanol, heptanol, carbenoxolone, oleamide, halothane, and 18-␣- and 18-␤glycyrrhetinic acid. Moreover, closure of hemichannels
formed by Cx30, Cx44, Cx46, Cx50, or Cx56 can be induced by hyperpolarization of the plasma membrane (137,
139, 205, 587, 599). In horizontal cells bathed in Ca2⫹-free
saline and exposed to positive holding potentials, open
hemichannels are closed by retinoic acid (678). With the
use of cysteine replacement mutagenesis, the voltage gate
in Cx46 hemichannels has been localized extracellularly
to the amino acid residue at position 35 (453). Extracellular acidification also closes hemichannels formed by
various connexins (28, 588, 676). The membrane current
mediated by hemichannels is greatly reduced by 1–2 mM
extracellular Ca2⫹ (137, 139, 454). It has been proposed
that Ca2⫹ induces a regional closure of the pore (454).
Mg2⫹ can partially substitute for the Ca2⫹ blocking effect
on Cx46 hemichannels (139).
The conductance of homomeric hemichannels
formed by Cx30, Cx32, Cx43, Cx45, Cx46, and Cx50 has
been measured using voltage clamp in the cell-attached or
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
cytes injected with the RNA of Cx46 (444). Shortly thereafter, DeVries and Schwartz (125) reported that cultured
solitary horizontal cells of the catfish retina express an
endogenous current mediated by hemichannels that open
upon reduction of the extracellular [Ca2⫹]. The current is
reduced by external [Ca2⫹] higher than 1 mM, treatment
with dopamine, or a weak acid and coincides with blockade of Lucifer yellow uptake. Subsequently, the electrophysiological characterization of macroscopic and single
hemichannel currents have been reported for various connexins exogenously expressed in Xenopus oocytes or
mammalian cell lines (137, 139, 205, 291, 341, 462, 471,
562, 589, 597, 599).
Opening of hemichannels formed by different connexin types is rather infrequent or absent under resting
conditions but can be regulated by several factors. Low
extracellular [Ca2⫹] enhances the opening of hemichannels in the Xenopus oocyte expression system (137, 139),
in Novikoff cells (341), in some cardiac myocytes (291), in
astrocytes (225, 562), and in transfected human osteoblast-like cells (492). In addition, opening of Cx43
hemichannels has been induced by mechanical stimulation in cultured astrocytes (562). Agonists of hemichannel
opening have also been described. The hemichannel-mediated currents expressed by retinal horizontal cells
bathed in low extracellular [Ca2⫹] are enhanced by the
antimalaric drugs quinidine or quinine (363). Quinineinduced dye uptake revealing opening of Cx43 hemichannels has also been observed in astrocytes (562), but not in
Cx43 RNA-injected Xenopus oocytes (644). The quinineinduced hemichannel opening cannot be explained solely
by the quinine-induced alkalinization because it is still
observed using 80 mM buffered HEPES in the recording
patch pipette (131). Alendronate, a drug used widely in
the treatment of bone diseases, induces opening of
hemichannels formed at least by Cx43 (462).
Lens connexins, including rat Cx46, bovine Cx44, and
chicken Cx56, form functional hemichannels in Xenopus
oocytes bathed in low or even normal extracellular [Ca2⫹]
(137, 139, 205, 444). However, lens fibers have high input
resistance, suggesting the absence of open hemichannels
at the plasma membrane under physiological conditions.
This apparent controversy might be explained by differences in the posttranscriptional modification of these
connexins in oocytes with respect to that in lens fibers.
These connexins are phosphoproteins and are detected as
multiple bands in immunoblots of lens homogenates (40,
205, 444), but when expressed in Xenopus oocytes, they
show the same electrophoretic mobilities as in vitro translated proteins (137, 205, 444). Sheep lens fibers containing
Cx49 show an increase in dye coupling when treated with
a casein kinase I inhibitor, suggesting that phosphorylation of the lens fiber connexin by the endogenous casein
kinase I activity leads to closure of gap junction channels
(89, 90). A similar mechanism might help in keeping lens
1371
1372
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
the excised-patch configuration (140, 149, 587, 597, 599).
The unitary conductance determined for homomeric connexin hemichannels ranges from 31 to 352 pS (140, 149,
587, 599).
In support of the existence of conduits permeable to
small molecules, it has been demonstrated that dextran
polymers of high molecular weight conjugated to different fluorophores are not taken up by cells expressing
hemichannels (99, 562). Moreover, it has been demonstrated that Cx43 hemichannels are permeable to Lucifer
yellow, ethidium bromide, carboxyfluorescein, 7-hydroxycoumarin-3-carboxylic acid, and fura 2 (99, 291, 341, 350,
462, 562, 607). Direct or indirect measurements have demonstrated the permeability of Cx43 hemichannels to other
small molecules [e.g., NAD⫹, ATP and inositol trisphosphate (IP3)] (15, 63, 64, 492, 562). Similarly, cells expressing Cx32 release ATP, suggesting that Cx32 hemichannels
are permeable to this nucleotide (15).
Alterations in hemichannel features by genetic mutation have also been documented. Two mutations linked to
congenital cataracts, Cx46Asn63Ser and Cx46 frame-shift
380, were impaired in their ability to form functional
Physiol Rev • VOL
hemichannels (438). Studies on Cx50 have revealed that
the His176Gln mutant is oocyte lethal and that the
His161Asn mutant does not form detectable hemichannels (28). Moreover, the double mutant Cx50His161Asn/
His176Gln neither forms hemichannels nor kills the oocytes (28). Hemichannels formed by a CMTX-associated
Cx32 mutant, Cx32Ser85Cys, show increased currents
compared with those made of wild-type Cx32 (2). A chimeric connexin consisting of Cx32 where the first extracellular loop sequence is replaced by the corresponding
Cx43 sequence induces a membrane conductance in single Xenopus oocytes (455). Finally, some carboxy-terminal mutations of Cx32, including some of those identified
in CMTX, prevent the formation of functional connexons
(79).
B. Hemichannel Functions
Recent reports indicate that hemichannel opening
could play relevant functions under physiological and
pathological conditions. Quist et al. (471) proposed that
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
FIG. 4. Schematic representation of possible activation routes of different protein kinases involved in Cx43
phosphorylation. Epidermal growth factor (EGF) binding to its receptor promotes receptor dimerization, autophosphorylation, and interaction with Grb2 adaptor protein and SOS guanine nucleotide exchange protein. Membrane-bound SOS
triggers the transformation of ras-GDP (p21ras-GDP) to the ras-GTP activated form (p21ras-GTP). Lysophosphatidic acid
(LPA) receptor (LBP) is coupled to G1 protein that also activates ras. EGF- or LPA-induced p21ras-GTP phosphorylates
raf-kinase (c-raf) leading to its activation. c-raf leads to MEK1/2 activation, which in turn leads to activation of
mitogen-activated protein kinase (MAPK). EGF or LPA-activated MAPK phosphorylates Cx43 on serine residues. Binding
of other ligands (L) to their membrane receptors (R) induces activation of Gq proteins, which induce activation of
phospholipase C (PLC). PLC converts phosphatidylinositol 4,5-bisphosphate (PIP2) to diacylglycerol (DAG) and inositol
1,4,5-trisphosphate (IP3). DAG activates protein kinase C (PKC), which in turn can phosphorylate MEK1/2 and MAPK
leading to their activation. The IP3-induced Ca2⫹ release from intracellular stores in the ER also promotes PKC
activation. PKC and PKC-activated MAPK can directly phosphorylate Cx43 on serine residues. Phosphorylation of Cx43
on tyrosine residues occurs by the expression of v-Src tyrosine kinase. v-Src interacts directly with Cx43 through its SH3
and SH2 domains catalyzing the phosphorylation of two tyrosine residues. [Modified from Warn-Cramer et al. (633).]
CONNEXIN CHANNELS
VII. GAP JUNCTIONS IN CARDIOVASCULAR,
DIGESTIVE, REPRODUCTIVE, AND
IMMUNE SYSTEMS
A. Cardiovascular System
Gap junctions between cardiac myocytes are found
in specialized plasma membrane regions known as the
intercalated disks adjacent to adherens junctions (which
facilitate mechanical coupling between cells). Gap junction channels in the heart appear to play a critical role by
allowing the intercellular passage of current-carrying
Physiol Rev • VOL
ions, which facilitates action potential propagation. Differences in the abundance, size, and location of gap junctions in different cardiac regions (117, 118) may contribute to differences in their properties of electrical conduction. As examples, Saffitz and colleagues (360, 512) have
shown that cardiac tissues that differ in their anisotropy
of conduction (infarct border zones vs. normal myocardium or crista terminalis vs. ventricular myocardium)
show marked differences in their relative abundance of
“end-to-end” versus “side-to-side” gap junctions. Moreover, because gap junction channels made of different
connexins have different conductance and gating properties, differences in expression patterns of connexins may
also contribute to differences in cardiac conduction.
Several connexins including Cx43, Cx40 (or its ortholog, chicken Cx42), and Cx45 are expressed in cardiac
tissues (266, 267), but they have different distributions in
specialized cardiac tissues. Cx43 appears to be the major
connexin in the working myocardium of the ventricle
(117, 118, 605). In atrial myocytes, Cx43 is coexpressed
with Cx40 (117, 118, 191, 512, 625). Studies of cardiac
tissues from several different species (human, dog, cow,
rabbit) have shown that Cx43 is rare or absent in cells of
the specialized conducting regions of the sinus and atrioventricular nodes (14, 117, 118, 307, 430, 431). However,
some studies have found Cx43-expressing cells that might
form specialized pathways for electrical conduction out
of nodal zones (307, 622, 623). The expression of Cx40 in
the heart is more restricted than that of Cx43. Cx40 is
abundant in atrial myocytes and cells of the His-Purkinje
system and is also found in cells of the sinoatrial and
atrioventricular nodes (24, 117, 191, 199, 266). Although
Cx40 is not present in adult mammalian ventricular myocytes, its ortholog (Cx42) is abundant in the ventricular
myocardium of the developing chicken heart (384). Cx45
expression is detectable in cells of the atria, ventricle,
sinus and atrioventricular nodes, and His bundle (117,
266). The absolute amounts of different connexins in
cardiac myocytes have not been determined; rather, different abundances have been considered based on the
intensity of immunostaining. This has led to some debate
regarding the significance of levels of Cx45 in ventricular
myocardium (101, 253).
Gap junctions are also present in distributions that
link all of the different cell types in the walls of blood
vessels. Gap junctions may play multiple roles in facilitating interactions between these cells (as recently reviewed
in Refs. 420, 532); most prominently, endothelial cell gap
junctions may be critical for the propagation of vasomotor signals (523). In general, all types of vessel wall cells
express Cx43, in vivo and in vitro. In vivo, Cx40 mRNA or
protein has been demonstrated in large and small vessel
endothelium and in smooth muscle from several species
but not others. Cx40 is a major gap junction protein of
endothelial cells of the adult vasculature in most organs
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
Cx43 hemichannels regulate the cell volume in response
to changes in extracellular physiological [Ca2⫹] in an
isosmotic situation. In addition, Cx43 hemichannels mediate the release of NAD⫹ to the extracellular medium in
fibroblasts (63, 64). This provides an answer to the old
paradox of having intracellular NAD⫹, the substrate for
CD38, an ectoenzyme that catalyzes the conversion of
NAD⫹ to cADPR (a potent physiological ligand for the
ryanodine receptor found in the ER). CD38 also mediates
the uptake of cADPR. A paracrine intercellular Ca2⫹ signaling through Cx43 hemichannel-mediated NAD⫹ efflux
has been proposed to enhance cell proliferation and
shorten the S phase of the cell cycle of NIH 3T3 fibroblasts (167). The existence of an autocrine cADPR-induced calcium release that regulates glutamate and GABA
release has been demonstrated in hippocampal astrocytes
(621). Furthermore, NAD⫹ efflux mediated by astrocytic
Cx43 hemichannels provides a paracrine signal mechanism that results in a delayed calcium transient in neuronal cells in coculture, which is strongly inhibited by glutamate receptor blockers (621). Moreover, mechanical
stimulation elicits release of ATP through Cx43 hemichannels in astrocytes and could mediate the propagation of
Ca2⫹ signals for intercellular communication in astrocytes and other nonexcitable cells (562).
The detection of Cx26 hemichannels on the dendrite
surface of retinal horizontal cells has been demonstrated
by immunofluorescence (262, 243). It has been proposed
that opening of Cx26 hemichannels would lead to depolarization of cell dendrites mediating a negative feedback
mechanism that modulates the activity of Ca2⫹ channels
and subsequent glutamate release from cones (262). Massive opening of hemichannels made of Cx43, the most
ubiquitous connexin, has been demonstrated in astrocytes and cardiomyocytes subjected to metabolic inhibition to mimic ischemia (99, 251, 291, 339). The metabolic
inhibition-induced opening of Cx43 hemichannels would
speed up mechanisms leading to cell death (99). Moreover, the increased opening of hemichannels made of a
CMTX-associated Cx32 mutant (Cx32Ser85Cys) could be
deleterious for glial cells and normal neural function (2).
1373
1374
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
(Cx43⫹/⫺). These mice appear phenotypically normal and
reproduce normally. However, epicardial conduction is
slowed in the ventricle (but not the atrium) (202, 576). In
addition, the QRS complex of the electrocardiogram is
widened, implying ventricular conduction delay (202,
576). Finally, tissue-specific knock-out strategies have
been used to produce mice with cardiac-specific loss of
Cx43; these animals show normal heart structure and
contractile function, but they develop sudden cardiac
death due to spontaneous ventricular arrhythmia by ⬃2
months of age (206). It has been recently suggested that
mutations in Cx43 associated with oculodentodigital dysplasia might be responsible for the cardiac conduction
abnormalities observed in some of the families (446).
An endothelial cell-specific Cx43 knock-out mouse
shows hypotension and bradycardia (343). The hypotensive and bradycardic phenotypes correlate with elevated
plasma levels of nitric oxide and angiotensins I and II,
suggesting the importance of Cx43 gap junctions for maintenance of vascular tone. An extensive series of transgenic experiments (using wild-type or mutant Cx43) by Lo
et al. (354) have emphasized the role of Cx43 expressed
by cardiac neural crest cells for the proper development
of the heart. For example, Huang et al. (235) have shown
that Cx43 gene dosage is critical for the function of neural
crest cells during cardiac development.
The importance of Cx40 in conduction through the
specialized cardiac conduction system is emphasized by
the analysis of Cx40-null mice. These animals develop to
adulthood and reproduce normally, suggesting that Cx40
is not necessary for cardiac development, since the cardiac structure and chambers appear normal. However,
electrocardiograms show wide and bizarre QRS complexes (47, 281, 542, 611) consistent with a right bundle
branch block pattern (likely due to the absence of this
connexin from the atrioventricular conduction pathways). These animals may also have defects in propagation of endothelium-dependent vasodilator responses
(127). Cx40-deficient mice retain gap junctional communication between aortic endothelial cells, although with
altered characteristics with respect to wild-type mice;
moreover, Cx37 and Cx43 are upregulated and redistributed (297), suggesting a compensatory mechanism. Cx40(and Cx37-)null animals exhibit no obvious vascular abnormalities.
Cx45-deficient mice die during embryogenesis due to
abnormalities of vascular development and cardiogenesis
(298, 299). Endothelial cell development and positioning
are normal, but further formation of vascular trees is
impaired and the smooth muscle layer of major arteries
fails to develop. The hearts of these animals are dilated,
and apoptosis is observed in almost all tissues by embryonic day 9.5.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
(346, 606), but it shows heterogeneous expression along
the vasculature (528). Other than expression in the ovary
and perhaps in some lung cells, Cx37 expression appears
to be virtually exclusively limited to endothelial cells
(478), but there may be substantial variability in expression in vivo and in culture, depending on vascular bed
type and species. The differential distribution of Cx37 and
Cx43 suggests that they are involved in more dynamic
processes than Cx40. However, interpretations of their
patterns of expression along vessel walls are controversial. Cx43 is highly localized to sites of disturbed flow in
rat aortic endothelium, but Cx37 and Cx40 are more
uniformly distributed (173). While arterial smooth muscle
cells abundantly express Cx43, they may also express
Cx40 (346) and Cx45 (222, 287, 298). The patterns of
expression of connexins among endothelial and smooth
muscle cells are modulated under pathological conditions
including early human coronary atherosclerosis or arterial wall injury (54, 208, 209, 305, 464, 465, 667).
Myocardial gap junctions and connexins may be critical for the coordinated electrical activation of the heart.
A variety of alterations in their number and distribution
have been observed in diseased hearts (265, 532). Disorganization of gap junctions and/or reduced expression of
Cx43 have been observed and may explain increased
arrhythmogenesis in human and animal ventricular myocardium associated with ischemia or infarction (452, 531).
Decreased Cx43 at plasma membrane appositions has
been found between cardiac myocytes infected with
Trypanosoma cruzi, the Chagas disease agent, suggesting a potential cause for cardiac conduction disturbances
observed in affected individuals (71). Levels of Cx40 increase 3.1-fold, and those of Cx43 decrease 3.3-fold in the
myocardium of hypertensive rats (24). In contrast, Cx40
levels were reduced, and its distribution was altered without any changes in Cx43 in association with models of
atrial fibrillation (603).
Recently, molecular biology approaches have been
used to alter the expression of cardiovascular connexins
to elucidate their functions. Reaume et al. (477) used
homologous recombination to produce Cx43-null mice.
These animals survive until birth and look essentially
normal. At birth, they have beating hearts, but they appear
cyanotic and die shortly thereafter, apparently due to a
lack of blood flow to their lungs due to obstruction of the
right ventricular outflow tract. Thus it appears that the
presence of Cx43 is not an absolute requirement for the
heart to beat or for the anatomic development of the
heart. Perhaps other coexpressed connexins (such as
Cx45) can explain the coupling of Cx43-null ventricular
myocytes, but the amount of Cx45 is also diminished in
Cx43-deficient mice (253).
The importance of Cx43 for normal cardiac conduction and velocity has been elucidated by studies of
mice that are heterozygous for the knock-out genotype
1375
CONNEXIN CHANNELS
B. Digestive System
1. Gastrointestinal tract
TABLE
Different cell types in the salivary glands contain
different connexins (Table 1). During the ontogeny of the
rat submandibular gland, Cx43 appears in myoepithelial
cells on gestational day 17, and Cx32 appears in acinar
cells on day 18 (237). The differential distribution of
connexins suggests that Cx26- and Cx32-containing junctions participate in the secretory function of acinar cells
and Cx43 participates in the contractile function of myoepithelial cells.
In the pancreas, connexin expression and gap junction function are very different in the exocrine and endocrine cells. Gap junctions are abundant, and Cx26 and
Cx32 are found in acinar cells (Table 1). As in other
secretory organs, it is believed that intercellular communication may enhance secretion by coordinating the response of coupled cells within an acini to a secretagogue
(378, 558). Functional gap junctions do not appear to be
1. Distribution of connexins in the digestive system
Segment/Organ
Oral cavity
Salivary glands
(Parotid, sublingual, and
submandibular glands)
Pancreas
Liver
Esophagus
Stomach
Gastroduodenal junction
Small intestine
Colon
2. Accessory glands
Connexins
Cell Type
Reference Nos.
26, 43
43
26, 32
43
Keratinocytes
Developing tooth
Acinar cells
Myoepithelial cells
513
461
224, 303, 396, 538
237, 396, 537, 591
26, 36, 43, 45
26, 32
26, 32
43
Endocrine ␤-cells
Exocrine cells
Hepatocytes
Stellate cells, oval cells, Kupffer cells, endothelial cells,
cholangiocytes, and cells of the Glisson capsule
Epithelial cells
Sphincter muscle cells
Epithelial cells
Muscle cells
Muscle cells
Cells of Cajal
Muscle cells
86, 379, 526
379
413, 585
41, 413, 585, 680
26,
45
26,
43
43,
40,
40,
43
32, 43
45
43, 45
43
Physiol Rev • VOL
83 • OCTOBER 2003 •
www.prv.org
159,
629
159,
238
159,
405,
629
652
308, 472, 568
177, 405
410, 524, 525, 629
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
Gap junctions, connexins, and functional intercellular coupling have been identified in multiple portions of
the gastrointestinal tract. The distribution of different
connexins in the various organs and tissues of the digestive system is shown in Table 1 based on a compilation of
diverse published studies. Along the gastrointestinal tract,
Cx26 and Cx32 are found in many of the epithelial cells,
whereas Cx43 is found in most of the smooth muscle
cells.
Within the intestine, gap junctions are present in the
circular muscle layer (reviewed in Ref. 114) where they
allow the formation of a muscular syncytium that can
synchronize contractile activity. Intestinal smooth muscle
cells are electrically coupled (1, 21, 143, 177, 212, 572),
and they show intercellular passage of microinjected dyes
(675). In contrast, gap junctions appear to be absent in the
longitudinal muscle layer (212), which may explain why
the contraction of canine duodenal circular muscle correlates much better with spike potentials than does contraction of longitudinal muscle.
Cells in different layers of the intestine may show
electrical (143, 572) but not dye coupling (675) with each
other. This coupling might be mediated indirectly through
interstitial cells and fibrocytes (572). Gap junctions between interstitial cells of Cajal of the guinea pig ileum
have recently been functionally demonstrated (31). Functional gap junctions between cells of Cajal and smooth
muscle cells have also been demonstrated (348), but their
role in the transmission of contraction signals is still a
matter of debate (113). Recently, reduced Cx43 expression has been observed in tissues from patients with
Hirschprung’s disease (410), suggesting that impaired intercellular communication between interstitial cells of
Cajal and smooth muscle cells may be partly responsible
for the motility dysfunction in this disease.
Several studies suggest a role for gap junctions in
gastric ulcers or cancers. The amount of Cx32 and Cx43 is
reduced in the mucosa surrounding a chronic gastric
ulcer, but it reverts to normal after antiulcer treatment
(383, 427). Blockade of rat gastric gland gap junctions
with 18␣-glycyrrhetinic acid prevents dye coupling, calcium wave propagation, and acid secretion (472). Moreover, gap junction blockade (induced with octanol) significantly inhibits the recovery of gastric mucosa from
acid-induced injury (568). It has also been proposed that
inhibition of gap junctions weakens the barrier function
of gastric mucosa and subsequently contributes to the
damaged barrier function following ischemia-reperfusion
(241). Moreover, analysis of tissue specimens from gastric
cancers has shown loss of Cx43 expression (427, 591).
1376
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
necessary for zymogen secretion, since dissociated pancreatic acinar cells show the same rate of exocytosis as
intact acini (72). However, connexin expression may be
necessary for proper control of secretory function, since
FIG. 5. Transfer of three different intercellular signals through gap
junctions. A and B: a phase-contrast micrograph of a pair of superior
cervical ganglion neurons is shown in A. Each neuron is impaled with a
microelectrode; one electrode is used to inject current into one of the
cells and the voltage deflections generated in each cell are recorded. An
example of one of those recordings is shown in B. This cell-cell signaling
corresponds to an electrotonic potential that propagates from one cell to
another in milliseconds or less. C and D: phase-contrast (C) and fluorescent (D) images of a cluster of MDCK cells in culture showing
intercellular transfer of Lucifer yellow. This process occurs by simple
diffusion through gap junctions and takes from several seconds to a
couple of minutes. F–L: levels of intracellular free [Ca2⫹] measured by
ratio imaging after loading the cells with fura 2. E: Nomarski image of a
hepatocyte triplet showing the microelectrode used for microinjections
into the top cell. F–H: intercellular propagation of a Ca2⫹ wave generated by the intracellular microinjection of IP3. The increase in intracellular free [Ca2⫹] in adjacent cells occurred sequentially and was not due
to Ca2⫹ diffusion because the increase in free [Ca2⫹] occurred in discrete cellular regions. I–L: intracellular free [Ca2⫹] measured in cells
bathed in Ca2⫹-free extracellular medium after Ca2⫹ was injected into
the cell with an electrode positioned as drawn. A localized increase in
intracellular free [Ca2⫹] was evident in the right side of the lower cell.
This occurred 2 s after Ca2⫹ microinjection and before visualization of
Ca2⫹ diffusion into the neighboring cell, suggesting that the microinjected Ca2⫹ induced the generation of a diffusible Ca2⫹-releasing agent
that permeated through gap junctions to the adjacent cell. This process
is regenerative and takes a few seconds. Magnification bar: 20 ␮m in A,
45 ␮m in E–L; 60 ␮m for C and D. [E-L modified from Sáez et al. (504).]
Physiol Rev • VOL
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
pancreatic amylase secretion is increased in Cx32-deficient mice (81). Gap junction function in pancreatic duct
cells may also contribute to the pancreatic dysfunction
observed in cystic fibrosis patients. Chloride currents
evoked by cAMP analogs increase intercellular cell coupling, and intercellular communication is impaired when
mutant cystic fibrosis transmembrane conductance regulator (CFTR) is expressed (83), but this effect is reversed
by transfection of wild-type CFTR (82).
In the endocrine islets of the pancreas, several connexins including Cx26, Cx43, and Cx45 have been found
(Table 1), but Cx36 now appears to be most involved in
insulin secretion. In Cx36-null mice, the development and
differentiation of ␤-cells are normal, but insulin secretion
in response to a glucose challenge is reduced (70). While
in vitro studies suggest that Cx43 expression is necessary
for insulin production (627), Cx43-null mouse embryos
have normal endocrine pancreatic ultrastructure, insulin
content, and secretion (86). The connexin type or abundance may also be crucial for the normal islet function,
since insulin secretion in response to glucose is reduced
in transgenic mice with targeted expression of Cx32 in
pancreatic ␤-cells despite increased levels of insulin, improved electrical synchronization, and increased intracellular calcium levels (85). It has been suggested that gap
junctions between islet cells are important for synchronizing glucose-induced intracellular calcium oscillations
(259). However, published evidence contradicts this hypothesis, since these calcium waves are not affected by
gap junction blockers and may be observed in the absence
of cell contacts (46).
CONNEXIN CHANNELS
Rodent hepatocytes are morphologically and metabolically heterogeneous, yet electrical coupling between
hepatocytes occurs over a relative long distance within
the liver (0.5 mm, ⬃25 hepatocytes), which accounts for
the similarity in membrane potentials among hepatocytes
(334). Consistent with the notion that gap junctions provide a pathway for synchronization of electrical rePhysiol Rev • VOL
sponses, the glucagon-induced hyperpolarization is higher
in periportal (Z1 zone) than in pericentral (Z3 zone) hepatocytes in isolated liver perfused with octanol, a gap
junction blocker (334). Moreover, dye coupling (119, 407)
and ligand-induced Ca2⫹ waves (393, 406, 490) have been
demonstrated in intact rat liver. Therefore, gap junctions
between hepatocytes allow propagation of electrotonic
potentials and Ca2⫹ waves as well as the intercellular
exchange of small molecules by simple diffusion (Fig. 5).
In rodent liver, the propagation of vasopressin-induced Ca2⫹ waves occurs in the absence of extracellular
Ca2⫹ (490), suggesting the participation of IP3-induced
Ca2⫹ release from intracellular stores instead of Ca2⫹
influx. These Ca2⫹ waves generated by a subthreshold
concentration of vasopressin propagate from terminal hepatic venules (THV) to terminal portal venules (TPV), a
direction opposite to the blood flow (Fig. 6), ruling out the
involvement of an ATP-mediated paracrine intercellular
communication mechanism at the apical region of the
cells. Moreover, perfusion of liver with ATP causes rapid
transient elevations in intracellular free [Ca2⫹] in single
hepatocytes or groups of hepatocytes throughout the lobule without a specific anatomic location for ATP-susceptible cells (393). In contrast, studies in rat hepatocyte
triplets or quadruplets (578) or in perfused liver (527)
have demonstrated that Ca2⫹ waves induced by vasopressin start at cells bearing high vasopressin receptor density, as proposed previously (41).
The propagation of Ca2⫹ waves would require as
mentioned above a regenerative system for increases in
intracellular [Ca2⫹] such as Ca2⫹-activated phospholipase
C and IP3 receptors (Fig. 6). It has been demonstrated that
IP3 also permeates hepatocyte gap junctions (504) and
that coordination of Ca2⫹ oscillations is fully dependent
on the intercellular diffusion of IP3 and not Ca2⫹ between
neighboring hepatocytes (95, 136). Immunofluorescence
studies have demonstrated the presence of protein Gq,
phospholipase C, and IP3 receptors in hepatocytes (223,
582). The importance of gap junctional communication
and IP3-sensitive Ca2⫹ stores in coordinating increases in
intracellular [Ca2⫹] between epithelial cells from a community with an heterogeneous density of vasopressin receptors has been demonstrated recently (336).
While nonparenchymal cells of the liver express
Cx43, hepatocytes express Cx26 and Cx32 (41, 188, 413,
585, 680). In hepatocytes, these connexins form homotypic and heterotypic gap junction channels as demonstrated by single-channel analysis in cells of Cx32-null and
wild-type mice (598). Cx26 and Cx32 gap junction channels show differences in permeability and charge selectivity when expressed in HeLa cells (73, 144). Hepatocytes
from Cx32-null mice show a strong reduction in IP3 permeability compared with wild-type hepatocytes (419).
Likewise, the intercellular propagation of IP3-induced
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
FIG. 6. The heterogeneous distribution of membrane receptors
determines the site of origin of Ca2⫹ waves that propagate across liver
acini. Top: schematic representation of a liver section showing a hepatic
acinus composed of hepatocytes located between two terminal hepatic
venules (THV). A portal triad constituted of a terminal portal venule
(TPV), an hepatic arteriole (HA), and a bile duct (BD) is depicted in the
center of the acinus. Z1, Z2, and Z3 denote liver zones specialized in
different metabolic pathways of the hemiacinus; Z1 hepatocytes are
more gluconeogenic, Z3 cells are more glycolytic, and Z2 cells show an
intermediate activity of both metabolic pathways. Middle: the gradients
of oxygen tension ([O2], light blue), the density of vasopressin receptors
(V1R, yellow), and the constant density of inositol trisphosphate receptors (IP3R, gray) throughout the acinus are represented. Bottom: diagram of Ca2⫹ wave propagation in a sinusoid. An hepatocyte triplet
formed by representative cells of each zone shows a gradient of V1
(yellow rectangles) receptor densities. Ca2⫹ waves generated by a subthreshold concentration of vasopressin (V) are born in Z3 and propagate
toward Z1. In each cell, IP3 induces Ca2⫹ release from ER stores. The
increase in [Ca2⫹] activates phospholipase C (PLC), which generates IP3
that permeates through gap junctions, thus leading to a regenerative
wave of IP3/Ca2⫹ that propagates to the adjacent cell. BC denotes bile
cannaliculi next to gap junction channels (illustrated by the 4 green
cylinders located at cellular interfaces).
1377
1378
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
C. Reproductive System
1. Gap junctions in the female reproductive system
Gap junctions interconnect cells in several different
tissues of the female reproductive system. In the ovarian
follicle, they are important for coordinating functions of
granulosa or stromal cells and for permitting interactions
of the developing oocyte with the surrounding follicular
cells. In the myometrium, they allow the electrical synchronization of muscle cells to facilitate contractions in
labor.
Ultrastructural studies have established the presence
of gap junctions between rat follicular cells (6, 183). Since
this observation, several connexins have been identified
in ovarian cells from different mammalian species, including Cx26, Cx32, Cx30.3, Cx37, Cx40, Cx41, Cx43, Cx45,
Physiol Rev • VOL
Cx57, and Cx60 (51, 192, 195, 240, 254, 368, 374, 421, 428,
541, 596, 672). Cx43 is very abundant and appears to be
the primary connexin connecting the granulosa cells (51).
Expression of Cx43 is evident in ovaries from sexually
mature animals, but not from fetuses (374). A cycle of
Cx43 expression has been detected during follicular
growth; Cx43 abundance is elevated before ovulation and
decreases when levels of luteinizing hormone are high
and during follicular atresia (194, 650, 651). However,
other investigators have detected gap junctions and Cx43
in the corpus luteum (275, 374). Thus ovarian Cx43 is
developmentally and hormonally regulated. Two mechanisms may be involved in the inhibition of ovarian Cx43
gap junction function during the maturation of the rat
oocyte: gating of gap junction channels due to increased
Cx43 phosphorylation (192) and inhibition of Cx43 expression (193). Lawrence et al. (333) established the functional ability of gap junctions between granulosa cells to
pass cAMP-dependent signals. Analyses of ovaries from
Cx43 mutant or null mice support a critical role for Cx43
gap junctions between granulosa cells in the regulation of
granulosa cell development. When these ovaries are studied in vitro or after grafting beneath the kidney capsule of
adult females, folliculogenesis can reach only the initial
steps (i.e., multilaminar follicles are absent in ovaries
from Cx43-null mice but present in ovaries from wild-type
mice) (4, 261). Similarly, maturation of bovine oocytes is
partially impaired by adenoviral transfection of cumulusoocyte complexes with an antisense Cx43 cDNA (626).
Gap junctions also link the growing female gamete
with its surrounding somatic cells in developing follicles
(13). This heterologous intercellular communication allows the cumulus cells to maintain the meiotic arrest of
the oocyte, since meiotic maturation resumes if intercellular communication is disrupted (183). There may be a
reciprocal transfer of signals through gap junctions between somatic cells and the oocyte in which follicular
cells provide signals for oocyte growth and the oocyte
provides regulatory signals for folliculogenesis (61, 148,
601, 602). It is likely that cAMP is the maturation inhibitory signal that is passed through gap junctions from the
granulosa cells to the oocyte (333, 636). Calcium signals
are also generated in cumulus cells and transported toward the oocyte in response to ATP (635), but they may
not be related to oocyte maturation. Cx37 is a critical
component of these heterocellular interactions, since this
protein is found between the developing oocyte and surrounding cumulus cells. Female Cx37-null mice are infertile and produce numerous inappropriate corpus lutea
(541). Follicle development arrests at the type 4 preantral
stage, and oocyte growth ceases at a diameter that is only
74% of control size; the oocytes arrest in a G2 state and
cannot enter M phase (initiate meiotic maturation) unless
treated with a phosphatase inhibitor (74).
In the uterus, gap junction structures are present
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
Ca2⫹ waves is three- to fourfold more efficient in Cx32
than in Cx26 transfected HeLa cells (418).
In support of the notion that hepatocytes require gap
junctional communication for an efficient metabolic response, it has been reported that Cx32-null mice show
close to a 70% reduction in nerve stimulation-induced
glucose release compared with wild-type mice (409). Similarly, Cx32-null mice show a drastic reduction in glucagon- and norephinephrine-induced glucose release (563).
Moreover, with the use of dissociated hepatocytes as well
as reaggregated hepatocytes and gap junction blockers, a
reduction of ⬃70% in vasopressin-induced glycogenolysis
has been observed (153). In addition to their involvement
in liver metabolic responses, gap junctions participate in
bile flow because 18␣-glycyrrhetinic acid exacerbates the
decrease induced by vasopressin (407). Cx32-null mice
also show a dilated bile canaliculi, and the nerve-dependent decrease in hepatic bile flow is attenuated drastically
(574).
A reduced number of gap junctions between hepatocytes occurs in liver cirrhosis and in chronic viral hepatitis (661), two pathological conditions likely to be associated with an inflammatory response. During liver inflammation, Cx26 and Cx32 are downregulated (119, 188),
a process that can be mimicked by soluble factors released by activated Kupffer cells (188). The inflammatory
response is a factor common to diverse pathologies; thus
reduced gap junctional communication might contribute
to the metabolic malfunctioning of the liver observed in
various diseases. In addition, several studies have demonstrated the role of gap junction in cell growth and
tumor promotion. In this respect, the incidence of liver
tumors in Cx32-null mice is much higher than in wild-type
animals (156, 573). The Cx32 deficiency enhances the
growth of liver tumors irrespective of the genetic background of the mouse strain used (385).
CONNEXIN CHANNELS
been demonstrated between Leydig cells (615). Cx26 and
Cx32 have not been found in Leydig cells (615) but are
present in the apical regions of the seminiferous epithelia
of mature rats (58, 489). Analysis of testes from neonatal
Cx43-null mice demonstrate that Cx43 is required for
germ line expansion, but not for steroidogenesis (261,
463, 494). In human testis, Cx43 is first expressed during
puberty (560).
Connexin expression in the rat testis and epididymis
is hormonally regulated. Human chorionic gonadotropin
administration in vivo and in vitro diminishes Cx43 mRNA
and protein in rat Leydig cells (673). Cx43 is differentially
expressed in an androgen-dependent manner by different
cells of the epididymis (107). Also, retinoid X receptor ␤
(RXR␤)-deficient mice exhibit abnormal spermatogenesis
due to altered Sertoli cell function and present decreased
levels of Cx43 transcripts (26). This suggests that retinoids, through the RXR␤ receptors, could be involved in
the control of Cx43 gene expression in Sertoli cells. As
described above, the expression of Cx43 can occur under
the control of c-jun transcriptional factors (460). It has
also been observed that jun-d-null mice are viable but
infertile; they present impaired spermatogenesis that correlates with a drastic reduction or abolishment of Cx43
expression (25). In agreement with these findings, immunohistochemical studies have shown a direct correlation
between severe spermatogenic impairment in men and
loss of Cx43 immunoreactivity in seminiferous tubules
(560). Thus gap junctions in testicular cells may play a
role in gonad development and spermatogenesis, and
their contribution may be critical to male fertility.
D. Immune System
2. Gap junctions in the male reproductive system
Several connexin mRNAs have been found in seminiferous tubules by RT-PCR analysis (488). Immunohistochemical studies have demonstrated that Cx43 is the most
prominent connexin in testes. Cx43 expression begins at
early stages of mouse embryonic gonads and increases
with time in Leydig and Sertoli cells (448, 450). A continuous increase in Cx43 expression is observed postnatally
until adulthood, when Cx43 expression in Sertoli cells
depends on the stage of the seminiferous epithelium (26,
58, 489). In rat testes, Cx33 colocalizes with Cx43 in
Sertoli-Sertoli gap junction plaques (571). The expression
of Cx33 is delayed with respect to that of Cx43 appearing
at postnatal day 15; Cx33 accumulates at Sertoli cell
interfaces until stage VII, the stage at which its expression
decreases together with that of Cx43 (571). Consistent
with these observations, in situ dye coupling has been
detected between Leydig cells, between peritubular cells,
between Sertoli cells, and between Sertoli and basal germ
cells in rodent species (26, 489). Electrical coupling has
Physiol Rev • VOL
Morphological and functional demonstration of gap
junctions and connexin identification in cells of the immune system (published between 1972 and 1999) has
been reviewed previously (11, 502, 503). This section
summarizes the latest reports with particular emphasis on
conditions that control the expression of connexins in
different cells and their possible functional roles in particular steps of the immune response.
With the use of in vivo and in vitro approaches, Cx43
and gap junctional communication have been identified in
the bone marrow between stromal cells and between
stromal and hematopoietic cells (295). It has been hypothesized that gap junctions participate in hematopoiesis,
and therefore, they may also play a role in leukemia (387,
497). However, Cx43-mediated communication between
stromal and hematopoietic stem cells may not be an
absolute requirement (496).
Gap junctions may provide a direct signaling pathway for transmigration, angiogenic, and metastatic processes. Recently, it has been demonstrated that HTLV-1-
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
connecting the smooth muscle cells of the myometrium
and connecting the epithelial cells of the endometrium.
Dramatic changes in the abundance of gap junctions and
intercellular communication precede the onset of labor
and likely facilitate the organization of uterine contraction during parturition (176). Cx43 is abundantly found
between the myometrial cells (51) and may be the most
important connexin for the regulation of uterine activity
associated with labor. However, multiple connexins have
been identified in these cells including Cx26, Cx40, and
Cx45 (7, 433). Cx43 is colocalized with Cx40 and with
Cx45 in myometrial smooth muscle (7, 278, 279). Cx26 has
been identified in the epithelium of the implantation
chamber of the pregnant, but not in nonpregnant or pseudo-pregnant rabbits (655). Cx26, Cx43, and Cx45 show
different temporal and cell type-specific patterns of expression during pregnancy and postpartum (51, 441, 485,
656).
The expression of myometrial Cx43 and Cx26 is hormonally regulated during the onset of labor. Rather than
the individual hormone levels, it appears that the increased ratio of estrogen to progesterone is the most
important factor. At term, Cx43 mRNA increases (by transcriptional regulation as discussed above) and Cx43 protein trafficking is altered (201, 213, 487). However, the
abundance of Cx43 in other organs is minimally affected
(486).
In the human, rat, mouse, and hamster oviduct, Cx43
and Cx26 have been identified between epithelial cells,
and Cx43 has been found between smooth muscle cells
(216). The abundance of connexins correlated with sexual
maturity, and the levels of Cx43 correlated with high
levels of estrogens (216).
1379
1380
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
parenchymal cells. In vitro treatment with tumor necrosis
factor (TNF)-␣ plus interferon (IFN)-␥ induces expression of Cx43 in human monocytes (151) and rodent microglia (152). TNF-␣ plus other yet unidentified factor(s)
released from activated endothelial cells induce Cx40 and
Cx43 in human polymorphonuclear cells (57). Moreover,
cerebral and hepatic fixed macrophages, microglia, and
Kupffer cells express at least Cx43 at inflammatory foci or
after treatment with proinflammatory agents (152, 188,
305, 465). Moreover, expression of Cx43 and Cx32 by
murine bone marrow cultured mast cells and the growth
factor-independent murine mast cell line C57 has been
documented (624). Nevertheless, the possible functional
role of these connexins remains unknown.
In agreement with the requirement for an increase in
intracellular calcium concentration for activation of cells
of the immune system, it has been found that a calcium
ionophore induces the expression of Cx43 in cultured rat
microglia (371). The increased levels of at least Cx43 by
monocytes/macrophages and microglia occur with an increase in the levels of Cx43 mRNA (371, 465), suggesting
activation of Cx43 mRNA transcription. In contrast to the
findings in myeloid and lymphoid cells, the expression of
connexins in endothelial (234, 609) and epithelial cells
such as hepatocytes (188) is reduced by cytokines.
Further studies may help elucidate the mechanisms
by which soluble factors control the expression of connexins and thus the formation of homocellular and heterocellular gap junctions between cells of the immune
system. The possible functional role of hemichannels in
the immune response has not been reported but deserves
to be studied.
VIII. GAP JUNCTION CHANNELS AND DISEASE
Gap junctions have been implicated in many cellular
processes, but the lack of specific blockers has limited the
study of their physiological role in vivo. New information
on the physiological roles of vertebrate connexins has
emerged from genetic studies. Mutations in connexin
genes correlate with a variety of human diseases, including demyelinating neuropathies, deafness, epidermal diseases, and lens cataracts. Genetic modification of connexins in mice has provided valuable information on connexin function and significance of their diversity. In
addition, targeted ablation of mouse connexin genes has
revealed basic insights into the functional diversity of the
connexin gene family.
A. Connexin Mutations Related to Human
Peripheral Neuropathy
The first disease demonstrated to rely on a connexin
mutation was the X-linked form of Charcot-Marie-Tooth
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
transformed lymphocytes (which are related to T-cell leukemia-lymphoma) form functional gap junctions with
endothelial cells in vitro (145). Nevertheless, inhibition of
gap junctions formed between human lymphocytes and
endothelial cells does not abolish lymphocyte transmigration through a human umbilical vein endothelial cell
monolayer (434). But, these cells do not form a tight
paracellular seal that would offer resistance for cell transmigration. Yet, gap junction blockers (octanol or 18␣glycyrrhetinic acid) reduce by ⬃60% the number of human monocytes that transmigrate across a blood-brain
barrier model (151).
In primary lymph nodes, functional coupling between
thymocytes as well as between thymocytes and thymic
epithelial cells has been demonstrated (10, 75). These cell
junctions are at least in part composed of Cx43 (10). In
secondary lymph organs, Cx43 has also been detected in
human follicular dendritic cells (294), and Cx40 and Cx43
are expressed in human tonsil-derived T and B lymphocytes (436). Moreover, dye coupling between human cultured dendritic cells and B lymphocytes (296) and Cx43
immunoreactivity between halogeneic mouse Langerhans
cells and T lymphocytes in culture (510) have been observed, suggesting the possible role of gap junctions in
antigen presentation and/or lymphocyte proliferation.
Moreover, synthetic peptides with sequence corresponding to a region of the extracellular loop 1 of connexins,
but not unrelated peptides, reduce the proliferation response of concanavalin A-stimulated lymphocytes (510).
In addition, the inhibition of B-lymphocyte gap junctions
with connexin-mimetic peptides or 18␣-glycyrrhetinic
acid drastically reduces the secretion of immunoglobulins
and the expression of interleukin-10 mRNA, suggesting
that intercellular communication mediated through gap
junctions favors these functions (435).
Epithelial and endothelial cell barriers, members of
the immune system, express connexins and form homocellular gap junctions (329, 346, 347, 532, 608) and could
form heterocellular gap junctions with migratory cells of
the immune system (204, 244, 369). Nevertheless, circulating nonactivated leukocytes, including monocytes,
polymorphonuclear cells, and lymphocytes, do not express, at least, Cx32, Cx40, or Cx43 (11, 57, 244, 465).
Consistent with the lack of connexin expression, gap
junctional communication has not been detected between
freshly isolated monocytes (12, 465), lymphocytes (510),
or polymorphonuclear cells (57). However, dye coupling
and Cx40 and Cx43 have been detected in T and/or B
lymphocytes freshly isolated from human blood (436),
raising controversy about connexin expression in these
cells. Species differences or isolation procedures, some of
which are known to induce cell activation, might explain
these differences.
Mediators of inflammation induce opposite effects on
gap junction expression in leukocytes and endothelial and
1381
CONNEXIN CHANNELS
gating properties are abnormal, thus impeding normal
intercellular communication (79, 124, 425, 429, 480). Yet,
one mutation restricts the channel pore diameter, possibly affecting the type of signaling molecules that cross
between adjacent loops of myelin (425). A mutant Cx32
(Ser85Cys) that forms functional gap junction channels
shows increased hemichannel currents with respect to
wild-type Cx32, a phenomenon that has been ascribed to
increased open probability (2). In this case, the loss of
ionic gradients and small metabolites and the increased
influx of Ca2⫹ through putative Cx32 hemichannels might
damage Schwann cells leading to the diseased state (2).
Rat Schwann cells also express Cx29, but its pattern of
distribution differs from that of Cx32 (8). In addition, low
levels of Cx43 have been detected in peripheral myelin
(364). Despite the expression of other connexin types in
myelinating cells, dysfunctions due to Cx32 mutations
predominate. Neuropathies due to mutations in other connexins may remain unrecognized if they are lethal due to
abnormalities caused in the other tissues where they are
expressed.
One intriguing aspect of the observed phenotype in
individuals carrying Cx32 mutants is that functional abnormalities are restricted to the peripheral nervous system. It is well documented that Cx32 is a major component of gap junctions in the liver and many other cell
types in different organs such as neurons, follicular cells,
pancreatic acinar cells, lacrimal acinar cells, and oligodendrocytes (67). Deletion of Cx32 in mice leads not only
FIG. 7. Myelin structure and location of connexin32 gap junction channels. The structure of peripheral myelin is shown at the top. The cytoplasm of
a Schwann cell wraps several times around a nerve
fiber (axon) forming the myelin sheath; several
Schwann cells form myelin around the same axon,
and the space not enwrapped by myelin is called the
node of Ranvier. An enlarged view of myelin is diagramed at the bottom (left, longitudinal section; right,
cross section); gap junction channels (⫽) formed between adjacent plasma membranes of the enwrapping
layers that originate from the same Schwann cell connect the incisures of Schmidt-Lanterman. [Modified
from White and Paul (647).]
Physiol Rev • VOL
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
disease (CMTX), a demyelinating syndrome associated
with Schwann cell defects that produce progressive degeneration of peripheral nerves. Cx32 protein is located in
the paranodal loops and Schmidt-Lantermann incisures in
myelinating Schwann cells (516) (Fig. 7). Cx32 channels
form intracellular connections between adjacent loops of
noncompacted myelin in one cell (reflexive gap junctions). These autocellular junctions provide a radial diffusion pathway between the Schwann cell nucleus and
adaxonal membranes that is ⬃300 times shorter than the
corresponding distance along the circumferential membrane (20). Communication through these junctions likely
provides metabolic and nutritional support for these bits
of cytoplasm. More than 160 CMTX-associated mutations
in the Cx32 gene have been identified since 1993 (3, 37).
Cx32 mutants identified in patients with CMTX include
missense, frameshift, deletion, and nonsense mutations.
Some of these mutations lead to complete loss of function
with no expression of functional channels (68, 79, 124,
425, 429, 480, 671). Mutations within the noncoding region
of the Cx32 gene have also been reported; some lead to a
reduced level or lack of Cx32 mRNA (239, 403), while
another affects mRNA translation (236). It has been described that SOX-10, a transcriptional factor responsible
for the expression of Cx32 and other myelin proteins, fails
to activate the mutated Cx32 promoter (56). Other mutant
forms of Cx32 fail to leave the Golgi apparatus, leading to
an abnormal accumulation in the cytoplasm (124). Other
Cx32 mutants form functional channels, but their voltage-
1382
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
B. Connexin Mutations Related to Deafness and
Skin Disorders
In mammals, Cx26 and Cx30 are expressed by nonsensory epithelial cells among which hair cells are dispersed, and by connective tissue cells at more distal
locations from hair cells (271, 277, 332). Connective tissue
cells, fibrocytes, and spiral ligaments and spiral limbs,
express at least Cx31 (658).
Congenital deafness is a very frequent disorder occurring in ⬃1 in 1,000 live births. Autosomal recessive
(DFNB1) and autosomal dominant (DFNA3) forms of genetic
deafness have been associated with more than 50 mutations
within the coding region of Cx26 [reviewed by Kelsell et
al. (273), White (641), and Lefebvre and van de Water
(335)]. (For an extensive list, visit the Connexins and
Deafness Homepage: http//www.iro.es/cx26deaf.htlm.)
Recessive mutations frequently result in a severely truncated Cx26 that is unlikely to retain any channel activity
(76, 121, 150, 272, 677). In contrast, dominant mutations
encode full-length products containing nonconservative
amino acid substitutions (80, 274, 392, 484, 646). The
Cx26Met34Thr mutant (274) was previously described as
a dominant negative, and in vitro data demonstrated that
the wild-type Cx26 could not form functional channels
when coexpressed with the mutant Cx26 (646). However,
some controversy about the interpretation of these results
has been raised by the frequent finding that individuals
Physiol Rev • VOL
heterozygous for the Cx26Met34Thr mutation have normal hearing (121, 272, 522). Although the precise role of
Cx26 in the etiology of nonsyndromic deafness remains
unknown, it has been proposed that junctional communication influences the ionic environment of the inner ear
sensory epithelia. Thus gap junctions would be involved
in recirculation of K⫹ from the interstitial space through
the syncytium formed by cochlear supporting cells (166,
257, 424), similar to the spatial buffering of K⫹ by astrocytes in the CNS. The use of Cx26-null mice to investigate
the role of Cx26 in the inner ear was not possible because
of its embryonic lethality (171). The role of Cx26 in cochlear function and cell survival has been demonstrated
recently after tissue-specific ablation of Cx26 (96). In
ear-specific homozygous Cx26(OtogCre)-null mice, the inner ear develops normally, but after the onset of hearing,
cell death is evident extending to the cochlear epithelial
network and sensory hair cells. These mice have hearing
impairment, but no vestibular dysfunction. Because cell
death initially affects the supporting cells of the inner hair
cell, it has been suggested that the inner hair cell response
to sound stimulation could be triggering the observed cell
death.
Some Cx26 mutations are also linked to skin disorders, such as palmoplantar keratoderma (164, 210, 273,
484). Mutations of Cx31 and Cx30 are also associated with
both deafness and epidermal disorders (197, 319, 483,
657). Recently, it has been shown that a new Cx26 mutation (Cx26⌬E42) associated with auditory and skin disorders inhibited the intercellular conductance in paired
Xenopus oocytes when coexpressed with wild-type Cx43
(498). These results suggest that dominant negative Cx26
mutations can produce a disease phenotype in the skin if
they interfere with the function of wild-type Cx43 also
found in the same cells.
C. Connexin Mutations Related
to Human Cataracts
The eye lens is an avascular organ formed by an
epithelial cell layer covering the anterior surface of the
organ and a large mass of fiber cells which form the bulk
of the organ. The fiber cells contain few organelles, yet
they must survive for the life span of the organism. Because there is no blood supply to the organ, most cells
receive their nutrients by diffusion from the aqueous humor in which the organ is suspended. Thus it has been
hypothesized that these cells are maintained by fluid, ion,
nutrient, and metabolite movement through an extensive
network of gap junctions (189). Mathias et al. (373) have
shown the presence of circulating currents in the lens that
would serve to drive water and ions between lens cells.
Several connexins have been identified in the lens. While
epithelial cells express Cx43 (51) and Cx50 (also known
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
to neuropathy but also to reduced nerve stimulation- and
hormone-induced hepatic glucose release (409, 563) and
reduced bile flow (574) following sympathetic stimulation, reduced fluid secretion by lacrimal glands (628), and
an increased amylase secretion from the exocrine pancreas (81). The absence of Cx32 results in a distinct
pattern of gene dysregulation in Schwann cells (415).
However, Cx32-null mice show a normal organization of
central nervous system myelin (517). This might result in
part from the distribution of Cx32 in the central nervous
system (i.e., mainly in oligodendrocyte cell bodies and
proximal processes, but not in paranodes) and from myelin differences between the parasympathetic nervous
system and the CNS (i.e., oligodendrocytes in central
nervous system wrap around axons less times, so the
width of the myelin sheath is smaller). Alternatively, the
functional role of Cx32 might be performed by other
connexins (e.g., Cx45 in the rat) that are coexpressed
with Cx32 in oligodendrocytes (301). In fact, some human
Cx32 mutations produce subclinical evidence of CNS dysfunction. These mutations, at least in vitro, do not produce a trans-dominant negative effect over Cx45 communication-competent HeLa cells (286), which would be in
agreement with the possibility of Cx45 compensating for
the lack of Cx32.
CONNEXIN CHANNELS
It remains to be determined whether heteromeric gap
junction channels made of Cx46 and Cx50 have different
permeability than homomeric Cx46 or Cx50 channels.
IX. PHYLOGENY
While functionally equivalent intercellular channels
and gap junction structures are found in many lower
multicellular organisms, no connexin genes have been
identified in any invertebrate organism (456). Invertebrate
gap junctions are made of protein subunits termed innexins which lack sequence homology with connexins, but do
exhibit similar membrane topology (175, 554). A phylogenetic study on connexins in working myocardium of chordates has demonstrated positive immunoreactivity in the
myocardium of Ascidian, a primitive chordate (30). In
turn, innexin family members have been detected in a
variety of animal phyla, including Platyhelminthes, Nematoda, Arthropoda, Mollusca, and Chordata. The finding
of two human innexin homologs would imply that intercellular communication might not only depend on the
distribution and activity of connexin-containing gap junctions, but also on that of innexins (439).
With the use of the Xenopus oocyte expression system, some of these proteins have been shown to form
functional gap junctions (324, 458) with pH and voltage
gating somewhat similar to those of vertebrate gap junctions (324). In the Caenorhabditis elegans genome, 25
innexins have been identified. Similar to vertebrates, C.
elegans tissues and single cells express more than one
innexin; some innexins are expressed in many tissues
while others show a more restricted pattern of expression
(555). In the fruitfly Drosophila, specific innexins play a
relevant role in the development of the gastrointestinal
tract (27) and the nervous system (105). Innexins are not
interchangeable in the development of neural function in
the Drosophila visual system (106). Cloning of an innexin
expressed in annelida has been recently described (467).
Reviews on gap junction in invertebrates have been reported (457, 555). The possibility of generating specific
mutants both in Drosophila melanogaster and C. elegans
will be an important approach to learn about the functional significance of gap junctions in different tissues of
invertebrates.
X. PERSPECTIVES
FIG. 8. Diagram of the eye lens. The regions of expression of
different connexins are indicated. The symbols “⬍” or “⬎” indicate the
relative levels of expression of connexins in the adult mammalian lens.
Cx46 and its chicken ortholog, Cx56, have also been reported to be
present in embryonic lens epithelium (249, 493). In this region, levels of
Cx46/Cx56 are much lower than those of Cx43. In mouse embryonic lens
cells, expression levels of Cx50 are higher than those of Cx46. In the
chicken embryo, Cx56 immunoreactivity in epithelial cells seems to be
more abundant than that of Cx45.6, the chicken ortholog of Cx50.
Physiol Rev • VOL
The introduction of new techniques and approaches
has increased our knowledge of gap junctions at several
levels. It is anticipated that in the near future they will
lead to an understanding of the multiplicity of different
connexins and which of their functions are unique or
common to other members of the family. Connexin mutants will allow identification of the molecular determi-
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
as MP70) (111), fiber cells express Cx46 and Cx50 in
mammals (285, 444, 642) or Cx56 and Cx45.6 in chickens
(40, 250, 500) (Fig. 8). The existence of gap junctions
connecting epithelial and fiber cells has been demonstrated with the dye coupling technique in the normal
adult rat lens (473). Accordingly, Cx43/Cx50 double
knock-out mice do not show dye coupling between epithelial and fiber lens cells (649).
Point mutations of the Cx50 and Cx46 genes have
been identified in patients with inherited zonular pulverulent cataract (361, 536). When expressed in Xenopus
oocytes, Cx46 and Cx50 mutations do not form functional
channels (437, 438). Similarly, the No2 mouse, which
develops congenital cataracts, carries a mutation within
the Cx50 sequence (559). Both Cx50-null and No2 mice
develop cataracts and exhibit microphtalmia (559, 646),
suggesting involvement of Cx50 in lens development. In
Xenopus oocytes, this mouse Cx50 mutant does not form
functional gap junctions (659). Recently published data
indicate that Cx43 and Cx50 are not required for prenatal
lens development but both are required for organ homeostasis (649). Cx46 knock-out mice exhibit normal lens
growth and development, but progressive cataractogenesis is evident 3 wk after birth (187). Because microphtalmia is present in Cx50- but not in Cx46-null mice, it has
been proposed that an early postnatal growth signal may
propagate through Cx50 but not Cx46 gap junction channels (647). Because Cx46- and Cx50-null mice develop
lens opacities, it is likely that channels made of a single
connexin type cannot compensate for the functional role
of gap junctions when both connexin types are expressed.
1383
1384
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
10.
NOTE ADDED IN PROOF
14.
Söhl et al. (544a) have suggested that the human ortholog
of mouse Cx29 corresponds to Cx30.2, while Altevogt et al. (8)
have suggested it corresponds to Cx31.3 due to the presence of
an intron within the carboxy terminus.
15.
8.
9.
11.
12.
13.
16.
We thank Helmuth Sánchez for the artwork of Figure 3.
This work was supported by Fondo Nacional de Investigación Cientı́fica y Tecnológica Grants 8990008 and 1030945 (to
J. C. Sáez), National Institutes of Health Grants HL-45466 and
EY-08368 (to E. C. Beyer), and a postdoctoral fellowship award
from the American Heart Association (to A. D. Martı́nez).
Address for reprint requests and other correspondence:
J. C. Sáez, Departamento de Ciencias Fisiológicas, Pontificia
Universidad Católica de Chile, Alameda 340, Santiago, Chile
(E-mail: [email protected]).
17.
18.
19.
REFERENCES
1. Abe Y and Tomita T. Cable properties of smooth muscle.
J Physiol 196: 87–100, 1968.
2. Abrams CK, Bennett MV, Verselis VK, and Bargiello TA. Voltage opens unopposed gap junction hemichannels formed by a
connexin 32 mutant associated with X-linked Charcot-Marie-Tooth
disease. Proc Natl Acad Sci USA 99: 3980 –3984, 2002.
3. Abrams CK, Oh S, Ri Y, and Bargiello TA. Mutations in connexin32: the molecular and biophysical bases for the X-linked form
of Charcot-Marie-Tooth disease. Brain Res Rev 32: 203–214, 2000.
4. Ackert CL, Gittens JE, O’Brien MJ, Eppig JJ, and Kidder GM.
Intercellular communication via connexin43 gap junctions is required for ovarian folliculogenesis in the mouse. Dev Biol 233:
258 –270, 2001.
5. Ahmad S and Evans WH. Post-translational integration and oligomerization of connexin 26 in plasma membranes and evidence of
formation of membrane pores: implications for the assembly of gap
junctions. Biochem J 365: 693– 699, 2002.
6. Albertini DF and Anderson E. The appearance and structure of
intercellular connections during the ontogeny of the rabbit ovarian
follicle with particular reference to gap junctions. J Cell Biol 63:
234 –250, 1974.
7. Albrecht JL, Atal NS, Tadros PN, Orsino A, Lye SJ, Sadovsky
Y, and Beyer EC. Rat uterine myometrium contains the gap juncPhysiol Rev • VOL
20.
21.
22.
23.
24.
25.
tion protein connexin45, which has a differing temporal expression
pattern from connexin43. Am J Obstet Gynecol 175: 853– 858, 1996.
Altevogt BM, Kleopa KA, Postma FR, Scherer SS, and Paul
DL. Connexin29 is uniquely distributed within myelinating glial
cells of the central and peripheral nervous systems. J Neurosci 22:
6458 – 6470, 2002.
Al-Ubaidi MR, White TW, Ripps H, Poras I, Avner P, Gomes D,
and Bruzzone R. Functional properties, developmental regulation,
and chromosomal localization of murine connexin36, a gap-junctional protein expressed preferentially in retina and brain. J Neurosci Res 59: 813– 826, 2000.
Alves LA, Campos de Carvalho AC, Lima EOC, Rocha e Souza
CM, Dardene M, Spray DC, and Savino W. Functional gap
junctions in thymic epithelial cells are formed by connexin 43. Eur
J Immunol 25: 431– 437, 1995.
Alves LA, Campos de Carvalho AC, and Savino W. Gap junctions: a novel route for direct cell-cell communication in the immune system? Immunol Today 19: 269 –275, 1998.
Alves LA, Coutinho-Silva R, Persechini PM, Spray DC, Savino
W, and Campos de Carvalho AC. Are there functional gap junctions or junctional hemichannels in macrophages? Blood 88: 328 –
334, 1996.
Anderson E and Albertini DF. Gap junctions between the oocyte
and companion follicle cells in the mammalian ovary. J Cell Biol 71:
680 – 686, 1976.
Anumonwo JM, Wang HZ, Trabka-Janik E, Dunham B, Veenstra RD, Delmar M, and Jalife J. Gap junctional channels in
adult mammalian sinus nodal cells: immunolocalization and electrophysiology. Circ Res 71: 229 –239, 1992.
Arcuino G, Lin JH, Takano T, Liu C, Jiang L, Gao Q, Kan J,
and Nedergaard M. Intercellular calcium signaling mediated by
point-source burst release of ATP. Proc Natl Acad Sci USA 99:
9840 –9845, 2002.
Asamoto M, Oyamada M, el-Aoumari A, Gros D, and Yamasaki
H. Molecular mechanisms of TPA-mediated inhibition of gap-junctional intercellular communication: evidence for action on the
assembly or function but not the expression of connexin 43 in rat
liver epithelial cells. Mol Carcinog 4: 322–327, 1991.
Bai S, Spray DC, and Burk RD. Identification of proximal and
distal regulatory elements of the rat connexin32 gene. Biochim
Biophys Acta 1216: 197–204, 1993.
Bailey J, Phillips RJ, Pollard AJ, Gilmore K, Robson SC, and
Europe-Finner GN. Characterization and functional analysis of
cAMP response element modulator protein and activating transcription factor 2 (ATF2) isoforms in the human myometrium
during pregnancy and labor: identification of a novel ATF2 species
with potent transactivation properties. J Clin Endocrinol Metab 87:
1717–1728, 2002.
Baldridge D, Lecanda F, Shin CS, Stains J, and Civitelli R.
Sequence and structure of the mouse connexin45 gene. Biosci Rep
21: 683– 689, 2001.
Balice-Gordon RJ, Bone LJ, and Scherer SS. Functional gap
junctions in the Schwann cell myelin sheath. J Cell Biol 142:
1095–1104, 1998.
Barr L, Berger W, and Dewey MM. Electrical transmission at the
nexus between smooth muscle cells. J Gen Physiol 51: 347–368,
1968.
Barr L, Dewey MM, and Berger W. Propagation of action potentials and the structure of the nexus in the cardiac muscle. J Gen
Physiol 48: 797– 823, 1965.
Barrio LC, Suchyna T, Bargiello TA, Xu LX, Roginski RS,
Bennett MV, and Nicholson BJ. Gap junctions formed by connexins 26 and 32 alone and in combination are differently affected
by applied voltage. Proc Natl Acad Sci USA 88: 8410 – 8414, 1991.
Bastide B, Neyses L, Ganten D, Paul M, Willecke K, and Traub
O. Gap junction protein connexin40 is preferentially expressed in
vascular endothelium and conductive bundles of rat myocardium
and is increased under hypertensive conditions. Circ Res 73: 1138 –
1149, 1993.
Batias C, Defamie N, Lablack A, Thepot D, Fenichel P, Segretain D, and Pointis G. Modified expression of testicular gapjunction connexin 43 during normal spermatogenic cycle and in
altered spermatogenesis. Cell Tissue Res 298: 113–121, 1999.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
nants of gating (e.g., voltage, pH, Ca2⫹, other chemicals),
permeability (to ions and molecules of different size), oligomerization with other connexins, docking of hemichannels, and interactions with other proteins. Structural studies of gap junctions at even higher resolution may elucidate the molecular events leading to closing and opening
of gap junction channels or hemichannels. The use of cell
type-specific promoters to knock out connexins in different cells or at different times during development will
clarify their roles. Conceivably, molecules that modify
channel/hemichannel behavior (including channel blockers) in a connexin type-specific manner will be identified,
allowing their use for pharmacological (and maybe therapeutic) purposes. Genetic studies may uncover additional diseases associated with other connexins. Finally,
the possible physiological role(s) of hemichannels may be
determined.
CONNEXIN CHANNELS
Physiol Rev • VOL
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
intercellular communication: consequences of connexin distribution and diversity. Braz J Med Biol Res 28: 415– 425, 1995.
Beyer EC, Kistler J, Paul DL, and Goodenough DA. Antisera
directed against connexin43 peptides react with a 43-kD protein
localized to gap junctions in myocardium and other tissues. J Cell
Biol 108: 595– 605, 1989.
Beyer EC, Paul DL, and Goodenough DA. Connexin43: a protein
from rat heart homologous to a gap junction protein from liver.
J Cell Biol 105: 2621–2629, 1987.
Beyer EC, Paul DL, and Goodenough DA. Connexin family of
gap junction proteins. J Membr Biol 116: 187–194, 1990.
Blackburn JP, Peters NS, Yeh HI, Rother YS, Green CR, and
Severs NJ. Upregulation of connexin-43 gap junctions during early
stages of human coronary atherosclerosis. Arterioscler Thromb
Vasc Biol 15: 1219 –1228, 1995.
Bondarev I, Vine A, and Bertram JS. Cloning and functional
expression of a novel human connexin-25 gene. Cell Commun
Adhes 8: 167–171, 2001.
Bondurand N, Girard M, Pingault V, Lemort N, Dubourg O,
and Goosens M. Human connexin 32, a gap junction protein
altered in the X-linked form of Charcot-Marie-Tooth disease, is
directly regulated by the transcription factor SOX10. Hum Mol
Genet 10: 2783–2795, 2001.
Brañes MC, Contreras JE, and Sáez JC. Activation of human
polymorphonuclear cells induces formation of functional gap junctions and expression of connexins. Med Sci Monit 8: BR313–BR323,
2002.
Bravo-Moreno JF, Dı́az-Sánchez V, Montoya-Flores JG,
Lamoyi E, Sáez JC, and Pérez-Armendáriz EM. Expression of
connexin43 in mouse Leydig, Sertoli, and germinal cells at different
stages of postnatal development. Anat Rec 264: 13–24, 2001.
Brink PR. Gap junction channel gating and permselectivity: their
roles in co-ordinated tissue function. Clin Exp Pharmacol Physiol
23: 1041–1046, 1996.
Brink PR. Gap junctions in vascular smooth muscle. Acta Physiol
Scand 164: 349 –356, 1998.
Brower PT and Schultz RM. Intercellular communication between granulosa cells and mouse oocytes: existence and possible
nutritional role during oocyte growth. Dev Biol 90: 144 –153, 1982.
Bruneau BG, Nemer G, Schmitt JP, Charron F, Robitaille L,
Caron S, Conner DA, Gessler M, Nemer M, Seidman CE, and
Seidman JG. A murine model of Holt-Oram syndrome defines
roles of the T-box transcription factor Tbx5 in cardiogenesis and
disease. Cell 106: 709 –721, 2001.
Bruzzone S, Franco L, Guida L, Zocchi E, Contini P, Bisso A,
Usai C, and De Flora A. A self-restricted CD38-connexin 43
cross-talk affects NAD⫹ and cyclic ADP-ribose metabolism and
regulates intracellular calcium in 3T3 fibroblasts. J Biol Chem 276:
48300 – 48308, 2001.
Bruzzone S, Guida L, Zocchi E, Franco L, and De Flora A.
Connexin 43 hemi channels mediate Ca2⫹-regulated transmembrane NAD⫹ fluxes in intact cells. FASEB J 15: 10 –12, 2001.
Bruzzone R and Ressot C. Connexins, gap junctions and cell-cell
signalling in the nervous system. Eur J Neurosci 9: 1– 6, 1997.
Bruzzone R, White TW, and Goodenough DA. The cellular
Internet: on-line with connexins. Bioessays 18: 709 –718, 1996.
Bruzzone R, White TW, and Paul DL. Connections with connexins: the molecular basis of direct intercellular signaling. Eur J Biochem 238: 1–27, 1996.
Bruzzone R, White TW, Scherer SS, Fischbeck KH, and Paul
DL. Null mutations of connexin32 in patients with X-linked Charcot-Marie Tooth disease. Neuron 13: 1253–1260, 1994.
Burt JM and Spray DC. Ionotropic agents modulate gap junctional conductance between cardiac myocytes. Am J Physiol Heart
Circ Physiol 254: H1206 –H1210, 1988.
Calabrese A, Guldenagel M, Charollais A, Mas C, Caton D,
Bauquis J, Serre-Beinier V, Caille D, Söhl G, Teubner B, Le
Gurun S, Trovato-Salinaro A, Condorelli DF, Haefliger JA,
Willecke K, and Meda P. Cx36 and the function of endocrine
pancreas. Cell Commun Adhes 8: 387–391, 2001.
Campos de Carvalho AC, Masuda MO, Tanowitz HB, Wittner
M, Goldenberg RC, and Spray DC. Conduction defects and
arrhythmias in Chagas’ disease: possible role of gap junctions and
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
26. Batias C, Siffroi JP, Fenichel P, Pointis G, and Segretain D.
Connexin43 gene expression and regulation in the rodent seminiferous epithelium. J Histochem Cytochem 48: 793– 805, 2000.
27. Bauer R, Lehmann C, and Hoch M. Gastrointestinal development
in the Drosophila embryo requires the activity of innexin gap
junction channel proteins. Cell Commun Adhes 8: 307–310, 2001.
28. Beahm DL and Hall JE. Hemichannel and junctional properties of
connexin 50. Biophys J 82: 2016 –2031, 2002.
29. Beardslee MA, Laing JG, Beyer EC, and Saffitz JE. Rapid
turnover of connexin43 in the adult rat heart. Circ Res 83: 629 – 635,
1998.
30. Becker DL, Cook JE, Davies CS, Evans WH, and Gourdie RG.
Expression of major gap junction connexin types in the working
myocardium of eight chordates. Cell Biol Int 22: 527–543, 1998.
31. Belzer V, Kobilo T, Rich A, and Hanani M. Intercellular coupling
among interstitial cells of Cajal in the guinea pig small intestine.
Cell Tissue Res 307: 15–21, 2002.
32. Belluardo N, Trovato-Salinaro A, Mudo G, Hurd YL, and Condorelli DF. Structure, chromosomal localization, and brain expression of human Cx36 gene. J Neurosci Res 57: 740 –752, 1999.
33. Benedetti EL and Emmelot P. Electron microscopic observations on negatively stained plasma membranes isolated from rat
liver. J Cell Biol 26: 299 –305, 1965.
34. Bennett MV. Physiology of electrotonic junctions. Ann NY Acad
Sci 137: 509 –539, 1966.
35. Bennett MV, Barrio LC, Bargiello TA, Spray DC, Hertzberg E,
and Sáez JC. Gap junctions: new tools, new answers, new questions. Neuron 6: 305–320, 1991.
36. Bennett MV and Verselis VK. Biophysics of gap junctions. Semin
Cell Biol 3: 29 – 47, 1992.
37. Bergoffen J, Scherer SS, Wang S, Scott MO, Bone LJ, Paul DL,
Chen K, Lensch MW, Chance PF, and Fischbek KH. Connexin
mutations in X-linked Charcot-Marie-Tooth disease. Science 262:
2039 –2042, 1993.
38. Berthoud VM, Bassnett S, and Beyer EC. Cultured chicken
embryo lens cells resemble differentiating fiber cells in vivo and
contain two kinetic pools of connexin56. Exp Eye Res 68: 475– 484,
1999.
39. Berthoud VM, Beyer EC, Kurata WE, Lau AF, and Lampe PD.
The gap-junction protein connexin 56 is phosphorylated in the
intracellular loop and the carboxy-terminal region. Eur J Biochem
244: 89 –97, 1997.
40. Berthoud VM, Cook AJ, and Beyer EC. Characterization of the
gap junction protein connexin56 in the chicken lens by immunofluorescence and immunoblotting. Invest Ophthalmol Vis Sci 35:
4109 – 4117, 1994.
41. Berthoud VM, Iwanij V, Garcia AM, and Sáez JC. Connexins
and glucagon receptors during development of rat hepatic acinus.
Am J Physiol Gastrointest Liver Physiol 263: G650 –G658, 1992.
42. Berthoud VM, Ledbetter ML, Hertzberg EL, and Sáez JC.
Connexin43 in MDCK cells: regulation by a tumor-promoting phorbol ester and Ca2⫹. Eur J Cell Biol 57: 40 –50, 1992.
43. Berthoud VM, Montegna EA, Atal N, Aithal NH, Brink PR, and
Beyer EC. Heteromeric connexons formed by the lens connexins,
connexin43 and connexin56. Eur J Cell Biol 80: 11–19, 2001.
44. Berthoud VM, Westphale EM, Grigoryeva A, and Beyer EC.
PKC isoenzymes in the chicken lens and TPA-induced effects on
intercellular communication. Invest Ophthalmol Vis Sci 41: 850 –
858, 2000.
45. Bertram JS. Carotenoids and gene regulation. Nutr Rev 57: 182–
191, 1999.
46. Bertuzzi F, Davalli AM, Nano R, Socci C, Codazzi F, Fesce R,
Di Carlo V, Pozza G, and Grohovaz F. Mechanisms of coordination of Ca2⫹ signals in pancreatic islet cells. Diabetes 48: 1971–
1978, 1999.
47. Bevilacqua LM, Simon AM, Maguire CT, Gehrmann J, Wakimoto H, Paul DL, and Berul CI. A targeted disruption in connexin40 leads to distinct atrioventricular conduction defects. J Interv Card Electrophysiol 4: 459 –567, 2000.
48. Beyer EC. Gap junctions. Int Rev Cytol 137C: 1–37, 1993.
49. Beyer EC and Berthoud VM. Gap junction synthesis and degradation as therapeutic targets. Curr Drug Targets 3: 409 – 416, 2002.
50. Beyer EC, Davis LM, Saffitz JE, and Veenstra RD. Cardiac
1385
1386
72.
73.
74.
75.
76.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
humoral mechanisms. J Cardiovasc Electrophysiol 5: 686 – 698,
1994.
Campos-Toimil M, Edwardson JM, and Thomas P. Acetylcholine-induced zymogen granule exocytosis: comparison between
acini and single pancreatic acinar cells. Pancreas 24: 179 –183,
2002.
Cao F, Eckert R, Elfgang C, Nitsche JM, Snyder SA, Hülser
DF, Willecke K, and Nicholson BJ. A quantitative analysis of
connexin-specific permeability differences of gap junctions expressed in HeLa transfectants and Xenopus oocytes. J Cell Sci 111:
31– 43, 1998.
Carabatsos MJ, Sellitto C, Goodenough DA, and Albertini
DF. Oocyte-granulosa cell heterologous gap junctions are required
for the coordination of nuclear and cytoplasmic meiotic competence. Dev Biol 226: 167–179, 2000.
Carolan EJ and Pitts JD. Some murine thymic lymphocytes can
form gap junctions. Immunol Lett 13: 255–260, 1986.
Carrasquillo MM, Zlotogora J, Barges S, and Chakravarti A.
Two different connexin 26 mutations in an inbred kindred segregating non-syndromic recessive deafness: implications for genetic
studies in isolated populations. Hum Mol Genet 6: 2163–2172, 1997.
Cascio M, Gogol E, and Wallace BA. The secondary structure of
gap junctions. Influence of isolation methods and proteolysis.
J Biol Chem 265: 2358 –2364, 1990.
Caspar DL, Goodenough DA, Makowski L, and Phillips WC.
Gap junction structures. I. Correlated electron microscopy and
X-ray diffraction. J Cell Biol 74: 605– 628, 1977.
Castro C, Gómez-Hernández JM, Silander K, and Barrio LC.
Altered formation of hemichannels and gap junction channels
caused by C-terminal connexin-32 mutations. J Neurosci 19: 3752–
3760, 1999.
Chaib H, Lina-Granade G, Guilford P, Plauchu H, Levilliers J,
Morgon A, and Petit C. A gene responsible for a dominant form
of neurosensory non-syndromic deafness maps to the NSRD1 recessive deafness gene interval. Hum Mol Genet 3: 2219 –2222, 1994.
Chanson M, Fanjul M, Bosco D, Nelles E, Suter S, Willecke K,
and Meda P. Enhanced secretion of amylase from exocrine pancreas of connexin32-deficient mice. J Cell Biol 141: 1267–1275,
1998.
Chanson M, Scerri I, and Suter S. Defective regulation of gap
junctional coupling in cystic fibrosis pancreatic duct cells. J Clin
Invest 103: 1677–1684, 1999.
Chanson M and Suter S. Regulation of gap junctional communication in CFTR-expressing pancreatic epithelial cells. Pflügers
Arch 443: S81–S84, 2001.
Chanson M, White MM, and Garber SS. cAMP promotes gap
junctional coupling in T84 cells. Am J Physiol Cell Physiol 271:
C533–C539, 1996.
Charollais A, Gjinovci A, Huarte J, Bauquis J, Nadal A, Martin F, Andreu E, Sánchez-Andrés JV, Calabrese A, Bosco D,
Soria B, Wollheim CB, Herrera PL, and Meda P. Junctional
communication of pancreatic beta cells contributes to the control
of insulin secretion and glucose tolerance. J Clin Invest 106: 235–
243, 2000.
Charollais A, Serre V, Mock C, Cogne F, Bosco D, and Meda P.
Loss of alpha 1 connexin does not alter the prenatal differentiation
of pancreatic beta cells and leads to the identification of another
islet cell connexin. Dev Genet 24: 13–26, 1999.
Chatterjee B, Li YX, Zdanoiwicz M, Sonntag JM, Chin AJ,
Kozlowski DJ, Valdimarsson G, Kirby ML, and Lo CW. Analysis
of Cx43alpha1 promoter function in the developing zebrafish embryo. Cell Commun Adhes 8: 289 –292, 2001.
Chen ZQ, Lefebvre D, Bai XH, Reaume A, Rossant J, and Lye
SJ. Identification of two regulatory elements within the promoter
region of the mouse connexin 43 gene. J Biol Chem 270: 3863–3868,
1995.
Cheng HL and Louis CF. Endogenous casein kinase I catalyzes
the phosphorylation of the lens fiber cell connexin49. Eur J Biochem 263: 276 –286, 1999.
Cheng HL and Louis CF. Functional effects of casein kinase
I-catalyzed phosphorylation on lens cell-to-cell coupling. J Membr
Biol 181: 21–30, 2001.
Christ GJ, Spray DC, El-Sabban M, Moore LK, and Brink PR.
Physiol Rev • VOL
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
105.
106.
107.
108.
109.
110.
111.
Gap junctions in vascular tissues. Evaluating the role of intercellular communication in the modulation of vasomotor tone. Circ
Res 79: 631– 646, 1996.
Church RL, Wang JH, and Steele E. The human lens intrinsic
membrane protein MP70 (Cx50) gene: clonal analysis and chromosome mapping. Curr Eye Res 14: 979 –981, 1995.
Cicirata F, Parenti R, Spinella F, Giglio S, Tuorto F, Zuffardi
O, and Gulisano M. Genomic organization and chromosomal
localization of the mouse Connexin36 (mCx36) gene. Gene 251:
123–130, 2000.
Civitelli R, Ziambaras K, Warlow PM, Lecanda F, Nelson T,
Harley J, Atal N, Beyer EC, and Steinberg TH. Regulation of
connexin43 expression and function by prostaglandin E2 (PGE2)
and parathyroid hormone (PTH) in osteoblastic cells. J Cell Biochem 68: 8 –21, 1998.
Clair C, Chalumeau C, Tordjmann T, Poggioli J, Erneux C,
Dupont G, and Combettes L. Investigation of the roles of Ca2⫹
and InsP(3) diffusion in the coordination of Ca2⫹ signals between
connected hepatocytes. J Cell Sci 114: 1999 –2007, 2001.
Cohen-Salmon M, Ott T, Michel V, Hardelin JP, Perfettini I,
Eybalin M, Wu T, Marcus DC, Wangemann P, Willecke K, and
Petit C. Targeted ablation of connexin26 in the inner ear epithelial
gap junction network causes hearing impairment and cell death.
Curr Biol 12: 1106 –1111, 2002.
Condorelli DF, Parenti R, Spinella F, Trovato-Salinaro A,
Belluardo N, Cardile V, and Cicirata F. Cloning of a new gap
junction gene (Cx36) highly expressed in mammalian brain neurons. Eur J Neurosci 10: 1202–1208, 1998.
Constantin B, Cronier L, and Raymond G. Transient involvement of gap junctional communication before fusion of newborn
rat myoblasts. C R Acad Sci III 320: 35– 40, 1997.
Contreras JE, Sánchez HA, Eugenı́n EA, Speidel D, Theis M,
Willecke K, Bukauskas FF, Bennett MVL, and Sáez JC. Metabolic inhibition induces opening of unapposed connexin 43 gap
junction hemichannels and reduces gap junctional communication
in cortical astrocytes in culture. Proc Natl Acad Sci USA 99: 495–
500, 2002.
Cooper CD, Solan JL, Dolejsi MK, and Lampe PD. Analysis of
connexin phosphorylation sites. Methods 20: 196 –204, 2000.
Coppen SR, Kodama I, Boyett MR, Dobrzynski H, Takagishi Y,
Honjo H, Yeh HI, and Severs NJ. Connexin45, a major connexin
of the rabbit sinoatrial node, is co-expressed with connexin43 in a
restricted zone at the nodal-crista terminalis border. J Histochem
Cytochem 47: 907–918, 1999.
Crow DS, Beyer EC, Paul DL, Kobe SS, and Lau AF. Phosphorylation of connexin43 gap junction protein in uninfected and Rous
sarcoma virus-transformed mammalian fibroblasts. Mol Cell Biol
10: 1754 –1763, 1990.
Cruciani V, Kaalhus O, and Mikalsen SO. Phosphatases involved in modulation of gap junctional intercellular communication and dephosphorylation of connexin43 in hamster fibroblasts:
2B or not 2B? Exp Cell Res 252: 449 – 463, 1999.
Cruciani V and Mikalsen SO. Stimulated phosphorylation of
intracellular connexin43. Exp Cell Res 251: 285–298, 1999.
Curtin KD, Zhang Z, and Wyman RJ. Gap junction proteins
expressed during development are required for adult neural function in the Drosophila optic lamina. J Neurosci 22: 7088 –7096,
2002.
Curtin KD, Zhang Z, and Wyman RJ. Gap junction proteins are
not interchangeable in development of neural function in the Drosophila visual system. J Cell Sci 115: 3379 –3388, 2002.
Cyr DG, Hermo L, and Laird DW. Immunocytochemical localization and regulation of connexin43 in the adult rat epididymis.
Endocrinology 137: 1474 –1484, 1996.
Dahl G. Where are the gates in gap junction channels? Clin Exp
Pharmacol Physiol 23: 1047–1052, 1996.
Dahl G, Levine E, Rabadan-Diehl C, and Werner R. Cell/cell
channel formation involves disulfide exchange. Eur J Biochem 197:
141–144, 1991.
Dahl G, Werner R, Levine E, and Rabadan-Diehl C. Mutational
analysis of gap junctional formation. Biophys J 62: 172–182, 1992.
Dahm R, van Marle J, Prescott AR, and Quinlan RA. Gap
junctions containing alpha8-connexin (MP70) in the adult mamma-
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
77.
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
CONNEXIN CHANNELS
112.
113.
114.
115.
116.
118.
119.
120.
121.
122.
123.
124.
125.
126.
127.
128.
129.
130.
131.
132.
133.
Physiol Rev • VOL
134.
135.
136.
137.
138.
139.
140.
141.
142.
143.
144.
145.
146.
147.
148.
149.
150.
151.
152.
153.
protein kinase C is required for cardiomyocyte connexin-43 phosphorylation. Circ Res 86: 293–301, 2000.
Donaldson P, Eckert R, Green C, and Kisler J. Gap junction
channels: new roles in disease. Histol Histopathol 12: 219 –231,
1997.
Duga S, Asselta R, Del Giacco L, Malcovati M, Ronchi S,
Tenchini ML, and Simonic T. A new exon in the 5⬘ untranslated
region of the connexin32 gene. Eur J Biochem 259: 188 –196, 1999.
Dupont G, Tordjmann T, Clair C, Swillens S, Claret M, and
Combettes L. Mechanism of receptor-oriented intercellular calcium wave propagation in hepatocytes. FASEB J 14: 279 –289, 2000.
Ebihara L, Berthoud VM, and Beyer EC. Distinct behavior of
connexin56 and connexin46 gap junctional channels can be predicted from the behavior of their hemi-gap-junctional channels.
Biophys J 68: 1796 –1803, 1995.
Ebihara L, Beyer EC, Swenson KI, Paul DL, and Goodenough
DA. Cloning and expression of a Xenopus embryonic gap junction
protein. Science 243: 1194 –1195, 1989.
Ebihara L and Steiner E. Properties of a nonjunctional current
expressed from a rat connexin46 cDNA in Xenopus oocytes. J Gen
Physiol 102: 59 –74, 1993.
Ebihara L, Xu X, Oberti C, Beyer EC, and Berthoud VM.
Co-expression of lens fiber connexins modifies hemi-gap-junctional
channel behavior. Biophys J 76: 198 –206, 1999.
Echetebu CO, Ali M, Izban MG, MacKay L, and Garfield RE.
Localization of regulatory protein binding sites in the proximal
region of human myometrial connexin 43 gene. Mol Hum Reprod 5:
757–766, 1999.
Eckert R, Dunina-Barkovskaya A, and Hülser D. Biophysical
characterization of gap-junction channels in HeLa cells. Pflügers
Arch 424: 335–342, 1993.
Elden L and Bortoff A. Electrical coupling of longitudinal and
circular intestinal muscle. Am J Physiol Gastrointest Liver Physiol
246: G618 –G626, 1984.
Elfgang C, Eckert R, Lichtenberg-Frate H, Butterweck A,
Traub O, Klein RA, Hülser DF, and Willecke K. Specific permeability and selective formation of gap junction channels in connexin-transfected HeLa cells. J Cell Biol 129: 805– 817, 1995.
El-Sabban ME, Merhi RA, Haidar HA, Arnulf B, Khoury H,
Basbous J, Nijmeh J, de The H, Hermine O, and Bazarbachi A.
Human T-cell lymphotropic virus type 1-transformed cells induce
angiogenesis and establish functional gap junctions with endothelial cells. Blood 99: 3383–3389, 2002.
Elvira M, Diez JA, Wang KKW, and Villalobo A. Phosphorylation of connexin-32 by protein kinase C prevents its proteolysis by
mu-calpain and m-calpain. J Biol Chem 268: 14294 –14300, 1993.
Endo K, Watanabe S, Nagahara A, Hirose M, and Sato N.
Restoration of gap junctions in the regenerative process of ethanolinduced gastric mucosal injury. J Gastroenterol Hepatol 10: 589 –
594, 1995.
Eppig JJ. A comparison between oocyte growth in coculture with
granulosa cells and oocytes with granulosa cell-oocyte junctional
contact maintained in vitro. J Exp Zool 209: 345–353, 1979.
Eskandari S, Zampighi GA, Leung DE, Wright EM, and Loo
DD. Inhibition of gap junction hemichannels by chloride channel
blockers. J Membr Biol 185: 93–102, 2002.
Estivill X, Fortina P, Surrey S, Rabionet R, Melchionda S,
D’Agruma L, Mansfield E, Rappaport E, Govea N, Mila M,
Zelante L, and Gasparini P. Connexin-26 mutations in sporadic
and inherited sensorineural deafness. Lancet 351: 394 –398, 1998.
Eugenı́n EA, Brañes MC, Berman JW, and Sáez JC. TNF-␣ and
IFN-␥ induce connexin-43 expression and formation of gap junctions between human monocytes/macrophages that enhance physiological responses. J Immunol 170: 1320 –1328, 2003.
Eugenı́n EA, Eckardt D, Theis M, Willecke K, Bennett MV,
and Sáez JC. Microglia at brain stab wounds express connexin 43
and in vitro form functional gap junctions after treatment with
interferon-␥ and tumor necrosis factor-␣. Proc Natl Acad Sci USA
98: 4190 – 4195, 2001.
Eugenı́n EA, González H, Sáez CG, and Sáez JC. Gap junctional
communication coordinates vasopressin-induced glycogenolysis in
rat hepatocytes. Am J Physiol Gastrointest Liver Physiol 274:
G1109 –G1116, 1998.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
117.
lian lens epithelium suggests a re-evaluation of its role in the lens.
Exp Eye Res 69: 45–56, 1999.
Daniel EE, Jury J, and Wang YF. nNOS in canine lower esophageal sphincter: colocalized with Cav-1 and Ca2⫹-handling proteins? Am J Physiol Gastrointest Liver Physiol 281: G1101–G1114,
2001.
Daniel EE, Thomas J, Ramnarain M, Bowes TJ, and Jury J. Do
gap junctions couple interstitial cells of Cajal pacing and neurotransmission to gastrointestinal smooth muscle? Neurogastroenterol Motil 13: 297–307, 2001.
Daniel EE and Wang YF. Gap junctions in intestinal smooth
muscle and interstitial cells of Cajal. Microsc Res Tech 47: 309 –320,
1999.
Darrow BJ, Laing JG, Lampe PD, Saffitz JE, and Beyer EC.
Expression of multiple connexins in cultured neonatal rat ventricular myocytes. Circ Res 76: 381–387, 1995.
Das Sarma J, Wang F, and Koval M. Targeted gap junction
protein constructs reveal connexin-specific differences in oligomerization. J Biol Chem 277: 20911–20918, 2002.
Davis LM, Kanter HL, Beyer EC, and Saffitz JE. Distinct gap
junction protein phenotypes in cardiac tissues with disparate conduction properties. J Am Coll Cardiol 24: 1124 –1132, 1994.
Davis LM, Rodefeld ME, Green K, Beyer EC, and Saffitz JE.
Gap junction protein phenotypes of the human heart and conduction system. J Cardiovasc Electrophysiol 6: 813– 822, 1995.
De Maio A, Gingalewski C, Theodorakis NG, and Clemens
MG. Interruption of hepatic gap junctional communication in the
rat during inflammation induced by bacterial lipopolysaccharide.
Shock 14: 53–59, 2000.
De Maio A, Vega VL, and Contreras JE. Gap junctions, homeostasis, and injury. J Cell Physiol 191: 269 –282, 2002.
Denoyelle F, Weil D, Maw MA, Wilcox SA, Lench NJ, AllenPowell DR, Osborn AH, Dahl HH, Middleton A, Houseman MJ,
Dodé C, Marlin S, Boulila-ElGaied A, Grati M, Ayadi H, BenArab S, Bitoun P, Lina-Granade G, Godet J, Mustapha M,
Loiselet J, El-Zir E, Aubois A, Joannard A, Levillers J, Garabédian EN, Mueller RF, McKinaly Gardner RJ, and Petit C.
Prelingual deafness: high prevalence of a 30delG mutation in the
connexin 26 gene. Hum Mol Genet 6: 2173–2177, 1997.
Dermietzel R. Gap junction wiring: a new principle in cell-to-cell
communication in the nervous system? Brain Res Rev 26: 176 –183,
1998.
Dermietzel R and Spray DC. Gap junctions in the brain: where,
what type, how many and why? Trends Neurosci 16: 186 –192, 1993.
Deschenes SM, Walcott JL, Wexler TL, Scherer SS, and Fischbeck KH. Altered trafficking of mutant connexin32. J Neurosci 17:
9077–9084, 1997.
DeVries SH and Schwartz EA. Hemi-gap-junction channels in
solitary horizontal cells of the catfish retina. J Physiol 445:201–230,
1992.
Dewey MM and Barr L. Intercellular connection between smooth
muscle cells: the nexus. Science 137: 670 – 672, 1962.
De Wit C, Roos F, Bolz SS, Kirchhoff S, Kruger O, Willecke K,
and Pohl U. Impaired conduction of vasodilation along arterioles
in connexin40-deficient mice. Circ Res 86: 649 – 655, 2000.
Dhein S. Gap junction channels in the cardiovascular system:
pharmacological and physiological modulation. Trends Pharmacol
Sci 19: 229 –241, 1998.
Diez JA, Ahmad S, and Evans WH. Assembly of heteromeric
connexons in guinea-pig liver en route to the Golgi apparatus,
plasma membrane and gap junctions. Eur J Biochem 262: 142–148,
1999.
Diez JA, Elvira M, and Villalobo A. The epidermal growth factor
receptor tyrosine kinase phosphorylates connexin32. Mol Cell Biochem 187: 201–210, 1998.
Dixon DB, Takahashi K, Bieda M, and Copenhagen DR. Quinine, intracellular pH and modulation of hemi-gap junctions in
catfish horizontal cells. Vision Res 36: 3925–3931, 1996.
Doble BW, Chen Y, Bosc DG, Litchfield DW, and Kardami E.
Fibroblast growth factor-2 decreases metabolic coupling and stimulates phosphorylation as well as masking of connexin43 epitopes
in cardiac myocytes. Circ Res 79: 647– 658, 1996.
Doble BW, Ping P, and Kardami E. The epsilon subtype of
1387
1388
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
176.
177.
178.
179.
180.
181.
182.
183.
184.
185.
186.
187.
188.
189.
190.
191.
192.
193.
194.
195.
Developmental expression and molecular characterization of two
gap junction channel proteins expressed during embryogenesis in
the grasshopper Schistocerca americana. Dev Genet 24: 137–150,
1999.
Garfield RE, Sims S, and Daniel EE. Gap junctions: their presence and necessity in myometrium during parturition. Science 198:
958 –960, 1977.
Garfield RE, Thilander G, Blennerhassett MG, and Sakai N.
Are gap junctions necessary for cell-to-cell coupling of smooth
muscle?: an update. Can J Physiol Pharmacol 70: 481– 490, 1992.
Geimonen E, Jiang W, Ali M, Fishman GI, Garfield RE, and
Andersen J. Activation of protein kinase C in human uterine
smooth muscle induces connexin-43 gene transcription through an
AP-1 site in the promoter sequence. J Biol Chem 271: 23667–23674,
1996.
George CH, Kendall JM, and Evans WH. Intracellular trafficking
pathways in the assembly of connexins into gap junctions. J Biol
Chem 274: 8678 – 8685, 1999.
Ghoshroy S, Goodenough DA, and Sosinsky GE. Preparation,
characterization, and structure of half gap junctional layers split
with urea and EGTA. J Membr Biol 146: 15–28, 1995.
Giepmans BN and Moolenaar WH. The gap junction protein
connexin43 interacts with the second PDZ domain of the zona
occludens-1 protein. Curr Biol 8: 931–934, 1998.
Giepmans BN, Verlaan I, Hengeveld T, Janssen H, Calafat J,
Falk MM, and Moolenar WH. Gap junction protein connexin-43
interacts directly with microtubules. Curr Biol 11: 1364 –1368,
2001.
Gilula NB, Epstein ML, and Beers WH. Cell-to-cell communication and ovulation. A study of the cumulus-oocyte complex. J Cell
Biol 78: 58 –75, 1978.
Gilula NB, Reeves OR, and Steinbach A. Metabolic coupling,
ionic coupling and cell contacts. Nature 235: 262–265, 1972.
Gingalewski C, Wang K, Clemens MG, and De Maio A. Posttranscriptional regulation of connexin 32 expression in liver during
acute inflammation. J Cell Physiol 166: 461– 467, 1996.
Godwin AJ, Green LM, Walsh MP, McDonald JR, Walsh DA,
and Fletcher WH. In situ regulation of cell-cell communication by
the cAMP-dependent protein kinase and protein kinase C. Mol Cell
Biochem 127–128: 293–307, 1993.
Gong X, Li E, Klier G, Huang Q, Wu Y, Lei H, Kumar NM,
Horwitz J, and Gilula NB. Disruption of alpha3 connexin gene
leads to proteolysis and cataractogenesis in mice. Cell 91: 833– 843,
1997.
González HE, Eugenı́n EA, Garcés G, Solı́s N, Pizarro M,
Accatino L, and Sáez JC. Regulation of hepatic connexins in
cholestasis: possible involvement of Kupffer cells and inflammatory mediators. Am J Physiol Gastrointest Liver Physiol 282:
G991–G1001, 2002.
Goodenough DA. Lens gap junctions: a structural hypothesis for
nonregulated low-resistance intercellular pathways. Invest Ophthalmol Vis Sci 18: 1104 –1122, 1979.
Goodenough DA, Goliger JA, and Paul DL. Connexins, connexons, and intercellular communication. Annu Rev Biochem 65: 475–
502, 1996.
Gourdie RG, Severs NJ, Green CR, Rothery S, Germroth P,
and Thompson RP. The spatial distribution and relative abundance of gap-junctional connexin40 and connexin43 correlate to
functional properties of components of the cardiac atrioventricular
conduction system. J Cell Sci 105: 985–991, 1993.
Granot I, Bechor E, Barash A, and Dekel N. Connexin43 in rat
oocytes: developmental modulation of its phosphorylation. Biol
Reprod 66: 568 –573, 2002.
Granot I and Dekel N. Phosphorylation and expression of connexin-43 ovarian gap junction protein are regulated by luteinizing
hormone. J Biol Chem 269: 30502–30509, 1994.
Granot I and Dekel N. Developmental expression and regulation
of the gap junction protein and transcript in rat ovaries. Mol Reprod
Dev 47: 231–239, 1997.
Grazul-Bilska AT, Redmer DA, Bilski JJ, Jablonka-Shariff A,
Doraiswamy V, and Reynolds LP. Gap junctional proteins, connexin 26, 32, and 43 in sheep ovaries throughout the estrous cycle.
Endocrine 8: 269 –279, 1998.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
154. Evans WH, Ahamad S, Dı́ez J, George CH, Kendall JM, and
Martin PE. Trafficking pathways leading to the formation of gap
junctions. In: Novartis Foundation Symposium. Gap JunctionMediated Intercellular Signaling in Health and Disease, edited by
Cardew G. London: Wiley, 1999, vol. 219, p. 44 –54.
155. Evans WH and Martin PE. Gap junctions: structure and function.
Mol Membr Biol 19: 121–136, 2002.
156. Evert M, Ott T, Temme A, Willecke K, and Dombrowski F.
Morphology and morphometric investigation of hepatocellular preneoplastic lesions and neoplasms in connexin32-deficient mice.
Carcinogenesis 23: 697–703, 2002.
157. Fallon RF and Goodenough DA. Five hour half-life of mouse
liver gap junction protein. J Cell Biol 90: 521–526, 1981.
158. Faucheux N, Dufresne M, and Nagel MD. Organization of cyclic
AMP-dependent connexin 43 in Swiss 3T3 cells attached to a
cellulose substratum. Biomaterials 23: 413– 421, 2002.
159. Fiertak A, Semik D, and Kilarski WM. Immunohistochemical
analysis of connexin26 and 43 expression in the mouse alimentary
tract. Folia Biol (Krakow) 47: 5–11, 1999.
160. Filson AJ, Azarnia R, Beyer EC, Loewenstein WR, and Brugge
JS. Tyrosine phosphorylation of a gap junction protein correlates
with inhibition of cell-to-cell communication. Cell Growth Differ 1:
661– 668, 1990.
161. Fishman GI, Eddy RL, Shows TB, Rosenthal L, and Leinwand
LA. The human connexin gene family of gap junction proteins:
distinct chromosomal locations but similar structures. Genomics
10: 250 –256, 1991.
162. Fishman GI, Moreno AP, Spray DC, and Leinwand LA. Functional analysis of human cardiac gap junction channel mutants.
Proc Natl Acad Sci USA 88: 3525–3529, 1991.
163. Fishman GI, Spray DC, and Leinwand LA. Molecular characterization and functional expression of the human cardiac gap junction channel. J Cell Biol 111: 589 –598, 1990.
164. Fitzgerald DA and Verbov JL. Hereditary palmoplantar keratoderma with deafness. Br J Dermatol 134: 939 –942, 1996.
165. Foote CI, Zhou L, Zhu X, and Nicholson BJ. The pattern of
disulfide linkages in the extracellular loop regions of connexin 32
suggests a model for the docking interface of gap junctions. J Cell
Biol 140: 1187–1197, 1998.
166. Forge A, Becker D, Casalotti S, Edwards J, Evans WH, Lench
N, and Souter M. Gap junctions and connexin expression in the
inner ear. In: Novartis Foundation Symposium. Gap JunctionMediated Intercellular Signaling in Health and Disease, edited by
Cardew G. London: Wiley, 1999, vol. 219, p. 134 –150.
167. Franco L, Zocchi E, Usai C, Guida L, Bruzzone S, Costa A, and
De Flora AG. Paracrine roles of NAD⫹ and cyclic ADP-ribose in
increasing intracellular calcium and enhancing cell proliferation of
3T3 fibroblasts. J Biol Chem 276: 21642–21648, 2001.
168. Froes M and Menezes J. Coupled heterocellular arrays in the
brain. Neurochem Int 41: 367–375, 2002.
169. Fujimoto K, Nagafuchi A, Tsukita S, Kuraoka A, Ohokuma A,
and Shibata Y. Dynamics of connexins, E-cadherin and alphacatenin on cell membranes during gap junction formation. J Cell
Sci 110: 311–322, 1997.
170. Furshpan EJ and Potter DD. Transmission at the giant motor
synapses of the crayfish. J Physiol 145: 289 –325, 1959.
171. Gabriel HD, Jung D, Butzler C, Temme A, Traub O, Winterhager E, and Willecke K. Transplacental uptake of glucose is
decreased in embryonic lethal connexin26-deficient mice. J Cell
Biol 140: 1453–1461, 1998.
172. Gabriel HD, Strobol B, Hellmann P, Buettner R, and Winterhager E. Organization and regulation of the rat Cx31 gene. Implication for a crucial role of the intron region. Eur J Biochem 268:
1749 –1759, 2001.
173. Gabriels JE and Paul DL. Connexin43 is highly localized to sites
of disturbed flow in rat aortic endothelium but connexin37 and
connexin40 are more uniformly distributed. Circ Res 83: 636 – 643,
1998.
174. Gaietta G, Deernick TJ, Adams SR, Bouver J, Tour O, Laird
DW, Sosinsky GE, Tsien RY, and Ellisman MH. Multicolor and
electron microscopic imaging of connexin trafficking. Science 296:
503–507, 2002.
175. Ganfornina MD, Sánchez D, Herrera M, and Bastiani MJ.
CONNEXIN CHANNELS
Physiol Rev • VOL
216.
217.
218.
219.
220.
221.
222.
223.
224.
225.
226.
227.
228.
229.
230.
231.
232.
233.
234.
235.
K. Molecular cloning of mouse connexins26 and -32: similar
genomic organization but distinct promoter sequences of two gap
junction genes. Eur J Cell Biol 58: 81– 89, 1992.
Hermoso M, Sáez JC, and Villalón M. Identification of gap
junctions in the oviduct and regulation of connexins during development and by sexual hormones. Eur J Cell Biol 74: 1–9, 1997.
Hertlein B, Butterweck A, Haubrich S, Willecke K, and Traub
O. Phosphorylated carboxy terminal serine residues stabilize the
mouse gap junction protein connexin45 against degradation. J
Membr Biol 162: 247–257, 1998.
Hertzberg EL, Disher RM, Tiller AA, Zhou Y, and Cook RG.
Topology of the Mr 27,000 liver gap junction protein. Cytoplasmic
localization of amino- and carboxyl termini and a hydrophilic domain which is protease-hypersensitive. J Biol Chem 263: 19105–
19111, 1988.
Hertzberg EL and Gilula NB. Isolation and characterization of
gap junctions from rat liver. J Biol Chem 254: 2138 –2147, 1979.
Heynkes R, Kozjek G, Traub O, and Willecke K. Identification
of a rat liver cDNA and mRNA coding for the 28 kDa gap junction
protein. FEBS Lett 205: 56 – 60, 1986.
Hill CS, Oh SY, Schmidt SA, Clark KJ, and Murray AW. Lysophosphatidic acid inhibits gap-junctional communication and stimulates phosphorylation of connexin-43 in WB cells: possible involvement of the mitogen-activated protein kinase cascade. Biochem J 303: 475– 479, 1994.
Hill CE, Rummery N, Hickey H, and Sandow SL. Heterogeneity
in the distribution of vascular gap junctions and connexins: implications for function. Clin Exp Pharmacol Physiol 29: 620 – 625,
2002.
Hirata K, Pusl T, O’Neill AF, Dranoff JA, and Nathanson MH.
The type II inositol 1,4,5-trisphosphate receptor can trigger Ca2⫹
waves in rat hepatocytes. Gastroenterology 122: 1088 –1100, 2002.
Hirono C, Shiba Y, and Kanno Y. Different localizations of 21 and
27 kDa gap-junction proteins in rat salivary glands. Histochem Cell
Biol 103: 39 – 46, 1995.
Hofer A and Dermietzel R. Visualization and functional blocking
of gap junction hemichannels (connexons) with antibodies against
external loop domains in astrocytes. Glia 24: 141–154, 1998.
Hoh JH, Sosinsky GE, Revel JP, and Hansma PK. Structure of
the extracellular surface of the gap junction by atomic force microscopy. Biophys J 65: 149 –163, 1993.
Holm I, Mikhailov A, Jillson T, and Rose B. Dynamics of gap
junctions observed in living cells with connexin43-GFP chimeric
protein. Eur J Cell Biol 78: 856 – 866, 1999.
Honjo H, Boyett MR, Coppen SR, Takagishi Y, Opthof T,
Severs NJ, and Kodama I. Heterogeneous expression of connexins in rabbit sinoatrial node cells: correlation between connexin
isotype and cell size. Cardiovasc Res 53: 89 –96, 2002.
Hossain MZ, Ao P, and Boynton AL. Platelet-derived growth
factor-induced disruption of gap junctional communication and
phosphorylation of connexin43 involves protein kinase C and mitogen-activated protein kinase. J Cell Physiol 176: 332–341, 1998.
Hossain MZ, Ao P, and Boynton AL. Rapid disruption of gap
junctional communication and phosphorylation of connexin43 by
platelet-derived growth factor in T51B rat liver epithelial cells
expressing platelet-derived growth factor receptor. J Cell Physiol
174: 66 –77, 1998.
Hossain MZ, Jagdale AB, Ao P, and Boynton AL. Mitogenactivated protein kinase and phosphorylation of connexin43 are
not sufficient for the disruption of gap junctional communication
by platelet-derived growth factor and tetradecanoylphorbol acetate. J Cell Physiol 179: 87–96, 1999.
Hossain MZ, Jagdale AB, Ao P, Kazlauskas A, and Boynton
AL. Disruption of gap junctional communication by the plateletderived growth factor is mediated via multiple signaling pathways.
J Biol Chem 274: 10489 –10496, 1999.
Hsieh CL, Kumar NM, Gilula NB, and Francke U. Distribution
of genes for gap junction membrane channel proteins on human
and mouse chromosomes. Somat Cell Mol Genet 17: 191–200, 1991.
Hu J and Cotgreave IA. Differential regulation of gap junctions
by proinflammatory mediators in vitro. J Clin Invest 99: 2312–2316,
1997.
Huang GY, Wessels A, Smith BR, Linask KK, Ewart JL, and Lo
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
196. Green CR, Harfst E, Goudie RG, and Severs NJ. Analysis of the
rat liver gap junction protein: clarification of anomalies in its
molecular size. Proc R Soc Lond B Biol Sci 233: 165–174, 1988.
197. Grifa A, Wagner CA, D’Ambrosio L, Melchionda S, Bernardi
F, López-Bigas N, Rabionet R, Arbones M, Monica MD, Estivill X, Zelante L, Lang F, and Gasparini P. Mutations in GJB6
cause nonsyndromic autosomal dominant deafness at DFNA3 locus. Nat Genet 23: 16 –18, 1999.
198. Groenewegen WA, van Veen TA, van der Velden HM, and
Jongsma HJ. Genomic organization of the rat connexin40 gene:
identical transcription start sites in heart and lung. Cardiovasc Res
38: 463– 471, 1998.
199. Gros D, Jarry-Guichard T, Ten Velde I, de Maziere A, van
Kempen MJ, Davoust J, Briand JP, Moorman AF, and
Jongsma HJ. Restricted distribution of connexin40, a gap junctional protein, in mammalian heart. Circ Res 74: 839 – 851, 1994.
200. Gros DB, Nicholson BJ, and Revel JP. Comparative analysis of
the gap junction protein from rat heart and liver: is there a tissue
specificity of gap junctions? Cell 35: 539 –549, 1983.
201. Grümmer R, Chwalisz K, Mulholland J, Traub O, and Winterhager E. Regulation of connexin26 and connexin43 expression in
rat endometrium by ovarian steroid hormones. Biol Reprod 51:
1109 –1116, 1994.
202. Guerrero PA, Schuessler RB, Davis LM, Beyer EC, Johnson
CM, Yamada KA, and Saffitz JE. Slow ventricular conduction in
mice heterozygous for a connexin43 null mutation. J Clin Invest 99:
1991–1998, 1997.
203. Guerrier A, Fonlupt P, Morand I, Rabilloud R, Audebet C,
Krutocskikh V, Gros D, Rousset B, and Munari-Silem Y. Gap
junctions and cell polarity: connexin32 and connexin43 expressed
in polarized thyroid epithelial cells assemble into separate gap
junctions, which are located in distinct regions of the lateral
plasma membrane domain. J Cell Sci 108: 2609 –2617, 1995.
204. Guinan EC, Smith BR, Davies PF, and Pober JS. Cytoplasmic
transfer between endothelium and lymphocytes: quantitation by
flow cytometry. Am J Pathol 132: 406 – 409, 1988.
205. Gupta VK, Berthoud VM, Atal N, Jarillo JA, Barrio LC, and
Beyer EC. Bovine connexin44, a lens gap junction protein: molecular cloning, immunologic characterization, and functional expression. Invest Ophtalmol Vis Sci 35: 3747–3758, 1994.
206. Gutstein DE, Morley GE, Tamaddon H, Vaidya D, Schneider
MD, Chen J, Chien KR, Stuhlmann H, and Fishman GI. Conduction slowing and sudden arrhythmic death in mice with cardiacrestricted inactivation of connexin43. Circ Res 88: 333–339, 2001.
207. Haefliger JA, Bruzzone R, Jenkins NA, Gilbert DJ, Copeland
NG, and Paul DL. Four novel members of the connexin family of
gap junction proteins. Molecular cloning, expression, and chromosome mapping. J Biol Chem 267: 2057–2064, 1992.
208. Haefliger JA and Meda P. Chronic hypertension alters the expression of Cx43 in cardiovascular muscle cells. Braz J Med Biol
Res 33: 431– 438, 2000.
209. Haefliger JA, Polikar R, Schnyder G, Burdet M, Sutter E,
Pexieder T, Nicod P, and Meda P. Connexin37 in normal and
pathological development of mouse heart and great arteries. Dev
Dyn 218: 331–344, 2000.
210. Heathcote K, Syrris P, Carter ND, and Paton MA. A connexin
26 mutation causes a syndrome of sensorineural hearing loss and
palmoplantar hyperkeratosis (MIM 148350). J Med Genet 37: 50 –51,
2000.
211. Henderson D, Eibl H, and Weber K. Structure and biochemistry
of mouse hepatic gap junctions. J Mol Biol 132: 193–218, 1979.
212. Henderson RM, Duchon G, and Daniel EE. Cell contacts in
duodenal smooth muscle layers. Am J Physiol 221: 564 –574, 1971.
213. Hendrix EM, Myatt L, Sellers S, Russell PT, and Larsen WJ.
Steroid hormone regulation of rat myometrial gap junction formation: effects on cx43 levels and trafficking. Biol Reprod 52: 547–560,
1995.
214. Hennemann H, Dahl E, White JB, Schwarz HJ, Lalley PA,
Chang S, Nicholson BJ, and Willecke K. Two gap junction
genes, connexin 31.1 and 30.3, are closely linked on chromosomes
4 and preferentially expressed in skin. J Biol Chem 267: 17225–
17233, 1992.
215. Hennemann H, Kozjek G, Dahl E, Nicholson B, and Willecke
1389
1390
236.
237.
238.
239.
240.
242.
243.
244.
245.
246.
247.
248.
249.
250.
251.
252.
253.
254.
255.
256.
CW. Alteration in connexin 43 gap junction gene dosage impairs
conotruncal heart development. Dev Biol 198: 32– 44, 1998.
Hudder A and Werner R. Analysis of a Charcot-Marie-Tooth
disease mutation reveals an essential internal ribosome entry site
element in the connexin-32 gene. J Biol Chem 275: 34586 –34591,
2000.
Ihara A, Muramatsu T, and Shimono M. Expression of connexin
32 and 43 in developing rat submandibular salivary glands. Arch
Oral Biol 45: 227–235, 2000.
Iino S, Asamoto K, and Nojyo Y. Heterogeneous distribution of
a gap junction protein, connexin43, in the gastroduodenal junction
of the guinea pig. Auton Neurosci 93: 8 –13, 2001.
Ionasescu VV, Searby C, Ionasescu R, Neuhaus IM, and
Werner R. Mutations of the noncoding region of the connexin32
gene in X-linked dominant Charcot-Marie-Tooth neuropathy. Neurology 47: 541–544, 1996.
Itahana K, Tanaka T, Morikazu Y, Komatu S, Ishida N, and
Takeya T. Isolation and characterization of a novel connexin gene,
Cx-60, in porcine ovarian follicles. Endocrinology 139: 320 –329,
1998.
Iwata F, Joh T, Ueda F, Yokoyama Y, and Itoh M. Role of gap
junctions in inhibiting ischemia-reperfusion injury of rat gastric
mucosa. Am J Physiol Gastrointest Liver Physiol 275: G883–G888,
1998.
Jacob A and Beyer EC. Mouse connexin 45: genomic cloning and
exon usage. DNA Cell Biol 20: 11–19, 2001.
Janssen-Bienhold U, Schultz K, Gelhaus A, Schmidt P, Ammermuller J, and Weiler R. Identification and localization of
connexin26 within the photoreceptor-horizontal cell synaptic complex. Vis Neurosci 18: 169 –178, 2001.
Jara PI, Boric MP, and Sáez JC. Leukocytes express connexin-43
after activation with lipopolysaccharide and appear to form gap
junctions with endothelial cells after ischemia-reperfusion. Proc
Natl Acad Sci USA 92: 7011–7015, 1995.
Jedamzik B, Marten I, Ngezahayo A, Ernst A, and Kolb HA.
Regulation of lens rCx46-formed hemichannels by activation of
protein kinase C, external Ca2⫹ and protons. J Membr Biol 173:
39 – 46, 2000.
Jiang JX and Googenough DA. Heteromeric connexons in lens
gap junction channels. Proc Natl Acad Sci USA 93: 1287–1291, 1996.
Jiang JX and Goodenough DA. Phosphorylation of lens-fiber
connexins in lens organ cultures. Eur J Biochem 255: 37– 44, 1998.
Jiang JX, Paul DL, and Goodenough DA. Posttranslational phosphorylation of lens fiber connexin46: a slow occurrence. Invest
Ophthal Visual Sci 34: 3558 –3565, 1993.
Jiang JX, White TW, and Goodenough DA. Changes in connexin
expression and distribution during chick lens development. Dev
Biol 168: 649 – 661, 1995.
Jiang JX, White TW, Goodenough DA, and Paul DL. Molecular
cloning and functional characterization of chick lens fiber connexin 45.6. Mol Biol Cell 5: 363–373, 1994.
John SA, Kondo R, Wang SY, Goldhaber JI, and Weiss JN.
Connexin-43 hemichannels opened by metabolic inhibition. J Biol
Chem 274: 236 –240, 1999.
John SA and Revel JP. Connexon integrity is maintained by
non-covalent bonds: intramolecular disulfide bonds link the extracellular domains in rat connexin-43. Biochem Biophys Res Commun 178: 1312–1318, 1991.
Johnson CM, Kanter EM, Green KG, Laing JG, Betsuyaku T,
Beyer EC, Steinberg TH, Saffitz JE, and Yamada KA. Redistribution of connexin45 in gap junctions of connexin43-deficient
hearts. Cardiovasc Res 53. 921–935, 2002.
Johnson ML, Redmer DA, Reynolds LP, and Grazul-Bilska AT.
Expression of gap junctional proteins connexin 43, 32, and 26
throughout follicular development and atresia in cows. Endocrine
10: 43–51, 1999.
Johnson R, Hammer M, Sheridan J, and Revel JP. Gap junction
formation between reaggregated Novikoff hepatoma cells. Proc
Natl Acad Sci USA 71: 4536 – 4540, 1974.
Johnson RG, Meyer RA, Li XR, Preuss DM, Tan L, Grunenwald H, Paulson AF, Laird DW, and Sheridan JD. Gap junctions
assemble in the presence of cytoskeletal inhibitors, but enhanced
assembly requires microtubules. Exp Cell Res 275: 67– 80, 2002.
Physiol Rev • VOL
257. Johnstone BM, Patuzzi R, Syka J, and Sykova E. Stimulusrelated potassium changes in the organ of Corti of guinea-pig.
J Physiol 408: 77–92, 1989.
258. Jongen WM, Fitzgerald DJ, Asamoto M, Piccoli C, Slaga JT,
Gros D, Takeichi M, and Yamasaki H. Regulation of connexin
43-mediated gap junctional intercellular communication by Ca2⫹ in
mouse epidermal cells is controlled by E-cadherin. J Cell Biol 114:
545–555, 1991.
259. Jonkers FC, Jonas JC, Gilon P, and Henquin JC. Influence of
cell number on the characteristics and synchrony of Ca2⫹ oscillations in clusters of mouse pancreatic islet cells. J Physiol 520:
839 – 849, 1999.
260. Jordan K, Chodock R, Hand AR, and Laird DW. The origin of
annular junctions: a mechanism of gap junction internalization.
J Cell Sci 114: 763–773, 2001.
261. Juneja SC, Barr KJ, Enders GC, and Kidder GM. Defects in the
germ line and gonads of mice lacking connexin43. Biol Reprod 60:
1263–1270, 1999.
262. Kamermans M, Fahrenfort I, Schultz K, Janssen-Bienhold U,
Sjoerdsma T, and Weiler R. Hemichannel-mediated inhibition in
the outer retina. Science 292: 1178 –1180, 2001.
263. Kanemitsu MY and Lau AF. Epidermal growth factor stimulates
the disruption of gap junctional communication and connexin43
phosphorylation independent of 12-O-tetradecanoylphorbol 13-acetate-sensitive protein kinase C: the possible involvement of mitogen-activated protein kinase. Mol Biol Cell 4: 837– 848, 1993.
264. Kanemitsu MY, Loo LW, Simon S, Lau AF, and Eckhart W.
Tyrosine phosphorylation of connexin 43 by v-Src is mediated by
SH2 and SH3 domain interactions. J Biol Chem 272: 22824 –22831,
1997.
265. Kanno S and Saffitz JE. The role of myocardial gap junctions in
electrical conduction and arrhythmogenesis. Cardiovasc Pathol 10:
169 –177, 2001.
266. Kanter HL, Laing JG, Beau SL, Beyer EC, and Saffitz JE.
Distinct patterns of connexin expression in canine Purkinje fibers
and ventricular muscle. Circ Res 72: 1124 –1131, 1993.
267. Kanter HL, Saffitz JE, and Beyer EC. Cardiac myocytes express
multiple gap junction proteins. Circ Res 70: 438 – 444, 1992.
268. Kardami E, Stoski RM, Doble BW, Yamamoto T, Hertzberg
EL, and Nagy JI. Biochemical and structural evidence for the
association of basic fibroblast growth factor with cardiac gap junctions. J Biol Chem 266: 19551–19557, 1991.
269. Karicheti V and Christ GJ. Physiological roles for K⫹ channels
and gap junctions in urogenital smooth muscle: implications for
improved understanding of urogenital function, disease and therapy. Curr Drug Targets 2: 1–20, 2001.
270. Keane RW, Mehta PP, Rose B, Honig LS, Loewenstein WR,
and Rutishauser U. Neural differentiation, N-CAM-mediated adhesion, and gap junctional communication in neuroectoderm. A
study in vitro. J Cell Biol 106: 1307–1319, 1988.
271. Kelley PM, Abe S, Askew JW, Smith SD, Usami S, and Kimberling WJ. Human connexin 30 (GJB6), a candidate gene for
nonsyndromic hearing loss: molecular cloning, tissue-specific expression, and assignment to chromosome 13q12. Genomics 62:
172–176, 1999.
272. Kelley PM, Harris DJ, Comer BC, Askew JW, Fowler T, Smith
SD, and Kimberling WJ. Novel mutations in the connexin 26 gene
(GJB2) that cause autosomal recessive (DFNB1) hearing loss. Am J
Hum Genet 62: 792–799, 1998.
273. Kelsell DP, Di WL, and Houseman MJ. Connexin mutations in
skin disease and hearing loss. Am J Hum Genet 68: 559 –568, 2001.
274. Kelsell DP, Dunlop J, Stevens HP, Lench NJ, Liang JN, Parry
G, Mueller RF, and Leigh IM. Connexin 26 mutations in hereditary non-syndromic sensorineural deafness. Nature 387: 80 – 83,
1997.
275. Khan-Dawood FS, Yang J, and Dawood MY. Expression of gap
junction protein connexin-43 in the human and baboon (Papio
anubis) corpus luteum. J Clin Endocrinol Metab 81: 835– 842,
1996.
276. Kiang DT, Jin N, Tu ZJ, and Lin HH. Upstream genomic sequence of the human connexin26 gene. Gene 199: 165–171, 1997.
277. Kikuchi T, Kimura RS, Paul DL, and Adams JC. Gap junctions
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
241.
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
CONNEXIN CHANNELS
278.
279.
280.
281.
283.
284.
285.
286.
287.
288.
289.
290.
291.
292.
293.
294.
295.
296.
Physiol Rev • VOL
297.
298.
299.
300.
301.
302.
303.
304.
305.
306.
307.
308.
309.
310.
311.
312.
313.
314.
315.
316.
317.
318.
to each other and to B lymphocytes. Eur J Immunol 27: 1489 –1497,
1997.
Krüger O, Beny JL, Chabaud F, Traub O, Theis M, Brix K,
Kirchhoff S, and Willecke K. Altered dye diffusion and upregulation of connexin37 in mouse aortic endothelium deficient in
connexin40. J Vasc Res 39: 160 –172, 2002.
Krüger O, Plum A, Kim JS, Winterhager E, Maxeiner S, Hallas
G, Kirchhoff S, Traub O, Lamers WH, and Willecke K. Defective vascular development in connexin 45-deficient mice. Development 127: 4179 – 4193, 2000.
Kumai M, Nishii K, Nakamura K, Takeda N, Suzuki M, and
Shibata Y. Loss of connexin45 causes a cushion defect in early
cardiogenesis. Development 127: 3501–3512, 2000.
Kumar NM and Gilula NB. Cloning and characterization of human and rat liver cDNAs coding for a gap junction protein. J Cell
Biol 103: 767–776, 1986.
Kunzelmann P, Blumcke I, Traub O, Dermietzel R, and Willecke K. Coexpression of connexin45 and -32 in oligodendrocytes
of rat brain. J Neurocytol 26: 17–22, 1997.
Kurata WE and Lau AF. p130gag-fps disrupts gap junctional communication and induces phosphorylation of connexin43 in a manner similar to that of pp60v-src. Oncogene 9: 329 –335, 1994.
Kuraoka A, Yamanaka I, Miyahara A, Shibata Y, and Uemura
T. Immunocytochemical studies of major gap junction proteins in
rat salivary glands. Eur Arch Otorhinolaryngol 251: S95–S99, 1994.
Kwak BR and Jongsma HJ. Selective inhibition of gap junction
channel activity by synthetic peptides. J Physiol 516: 679 – 685,
1999.
Kwak BR, Mulhaupt F, Veillard N, Gros DB, and Mach F.
Altered pattern of vascular connexin expression in atherosclerotic
plaques. Arterioscler Thromb Vasc Biol 22: 225–230, 2002.
Kwak BR, Sáez JC, Wilders RW, Chanson M, Fishman GL,
Hertzberg EL, Spray DC, and Jongsma HJ. Effects of cGMPdependent phosphorylation on rat and human connexin43 gap
junction channels. Pflügers Arch 430: 770 –778, 1995.
Kwong KF, Schuessler RB, Green KG, Laing JG, Beyer EC,
Boineau JP, and Saffitz JE. Differential expression of gap junction proteins in the canine sinus node. Circ Res 82: 604 – 612, 1998.
Kyoi T, Ueda F, Kimura K, Yamamoto M, and Kataoka K.
Development of gap junctions between gastric surface mucous
cells during cell maturation in rats. Gastroenterology 102: 1930 –
1935, 1992.
Laing JG and Beyer EC. The gap junction protein connexin43 is
degraded via the ubiquitin proteasome pathway. J Biol Chem 270:
26399 –26403, 1995.
Laing JG, Manley-Markowski RN, Koval M, Civitelli R, and
Steinberg TH. Connexin45 interacts with zonula occludens-1 and
connexin43 in osteoblastic cells. J Biol Chem 276: 23051–23055,
2001.
Laing JG, Tadros PN, Green K, Saffitz JE, and Beyer EC.
Proteolysis of connexin43-containing gap junctions in normal and
heat-stressed cardiac myocytes. Cardiovasc Res 38: 711–718, 1998.
Laing JG, Tadros PN, Westphale EM, and Beyer EC. Degradation of connexin43 gap junctions involves both the proteasome and
the lysosome. Exp Cell Res 236: 482– 492, 1997.
Laing JG, Westphale EM, Engelmann GL, and Beyer EC. Characterization of the gap junction protein, connexin45. J Membr Biol
139: 31– 40, 1994.
Laird DW. The life cycle of a connexin: gap junction formation,
removal, and degradation. J Bioenerg Biomembr 28: 311–318, 1996.
Laird DW, Castillo M, and Kasprzak L. Gap junction turnover,
intracellular trafficking, and phosphorylation of connexin43 in
brefeldin A-treated rat mammary tumor cells. J Cell Biol 131:
1193–1203, 1995.
Laird DW, Puranam KL, and Revel JP. Turnover and phosphorylation dynamics of connexin43 gap junction protein in cultured
cardiac myocytes. Biochem J 273: 67–72, 1991.
Laird DW and Sáez JC. Posttranscriptional events in expression
of gap junctions. In: Advances in Molecular Cell Biology, edited by
Hertzberg EL. Greenwich: JAI, 2000, vol 18, p. 99 –128.
Lal R, John SA, Laird DW, and Arnsdorf MF. Heart gap junction
preparations reveal hemiplaques by atomic force microscopy. Am J
Physiol Cell Physiol 268: C968 –C977, 1995.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
282.
in the rat cochlea-immunohistochemical and ultrastructural analysis. Anat Embryol (Berl) 191: 101–118, 1995.
Kilarski WM, Dupont E, Coppen S, Yeh HI, Vozzi C, Gourdie
RG, Rezapour M, Ulmsten U, Roomans GM, and Severs NJ.
Identification of two further gap-junctional proteins, connexin40
and connexin45, in human myometrial smooth muscle cells at
term. Eur J Cell Biol 75: 1– 8, 1998.
Kilarski WM, Rothery YS, Roomans GM, Ulmsten U, Rezapour
M, Stevenson S, Coppen SR, Dupont E, and Severs NJ. Multiple connexins localized to individual gap-junctional plaques in
human myometrial smooth muscle. Microsc Res Tech 54: 114 –122,
2001.
Kim DY, Kam Y, Koo SK, and Joe CO. Gating connexin 43
channels reconstituted in lipid vesicles by mitogen-activated protein kinase phosphorylation. J Biol Chem 274: 5581–5587, 1999.
Kirchhoff S, Kim JS, Hagendorff A, Thonnissen E, Kruger O,
Lamers WH, and Willecke K. Abnormal cardiac conduction and
morphogenesis in connexin40 and connexin43 double-deficient
mice. Circ Res 87: 399 – 405, 2000.
Kistler J, Bond J, Donaldson P, and Engel A. Two distinct
levels of gap junction assembly in vitro. J Struct Biol 110: 28 –38,
1993.
Kistler J and Bullivant S. Protein processing in lens intercellular
junctions: cleavage of MP70 to MP38. Invest Ophthalmol Vis Sci 28:
1687–1692, 1987.
Kistler J, Christie D, and Bullivant S. Homologies between gap
junction proteins in lens, heart and liver. Nature 331: 721–723, 1988.
Kistler J, Kirkland B, and Bullivant S. Identification of a
70,000-D protein in lens membrane junctional domains. J Cell Biol
101: 28 –35, 1985.
Kleopa KA, Yum SW, and Scherer SS. Cellular mechanisms of
connexin32 mutations associated with CNS manifestations. J Neurosci Res 68: 522–534, 2002.
Ko YS, Coppen SR, Dupont E, Rother YS, and Severs NJ.
Regional differentiation of desmin, connexin43, and connexin45
expression patterns in rat aortic smooth muscle. Arterioscler
Thromb Vasc Biol 21: 355–364, 2001.
Kojima T, Kokai Y, Chiba H, Yamamoto M, Mochizuki Y, and
Sawada N. Cx32 but not Cx26 is associated with tight junctions in
primary cultures of rat hepatocytes. Exp Cell Res 263: 193–201,
2001.
Kojima T, Sawada N, Chiba H, Kokai Y, Yamamoto M, Urban
M, Lee GH, Hertzberg EL, Mochizuki Y, and Spray DC. Induction of tight junctions in human connexin 32 (hCx32)-transfected
mouse hepatocytes: connexin 32 interacts with occludin. Biochem
Biophys Res Commun 266: 222–229, 1999.
Kojima T, Spray DC, Kokai Y, Chiba H, Mochizuki Y, and
Sawada N. Cx32 formation and/or Cx32-mediated intercellular
communication induces expression and function of tight junctions
in hepatocytic cell line. Exp Cell Res 276: 40 –51, 2002.
Kondo RP, Wang SY, John SA, Weiss JN, and Goldhaber JI.
Metabolic inhibition activates a non-selective current through connexin hemichannels in isolated ventricular myocytes. J Mol Cell
Cardiol 32: 1859 –1872, 2000.
Koval M, Geist ST, Westphale EM, Kemendy AE, Civitelli R,
Beyer EC, and Steinberg TH. Transfected connexin45 alters gap
junction permeability in cells expressing endogenous connexin43.
J Cell Biol 130: 987–995, 1995.
Kren BT, Kumar NM, Wang SQ, Gilula NB, and Steer CJ.
Differential regulation of multiple gap junction transcripts and
proteins during rat liver regeneration. J Cell Biol 123: 707–718,
1993.
Krenacs T and Rosendaal M. Immunohistological detection of
gap junctions in human lymphoid tissue: connexin43 in follicular
dendritic and lymphoendothelial cells. J Histochem Cytochem 43:
1125–1137, 1995.
Krenacs T and Rosendaal M. Connexin43 gap junctions in normal, regenerating, and cultured mouse bone marrow and in human
leukemias: their possible involvement in blood formation. Am J
Pathol 152: 993–1004, 1998.
Krenacs T, van Dartel M, Lindhout E, and Rosendaal M. Direct
cell/cell communication in the lymphoid germinal center: connexin43 gap junctions functionally couple follicular dendritic cells
1391
1392
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
340. Li GY, Lin HH, Tu ZJ, and Kiang DT. Gap junction Cx26 gene
modulation by phorbol esters in benign and malignant human
mammary cells. Gene 209: 139 –147, 1998.
341. Li H, Liu TF, Lazrak A, Peracchia C, Goldberg GS, Lampe PD,
and Johnson RG. Properties and regulation of gap junctional
hemichannels in the plasma membranes of cultured cells. J Cell
Biol 134: 1019 –1030, 1996.
342. Li WE and Nagy JI. Connexin43 phosphorylation state and intercellular communication in cultured astrocytes following hypoxia
and protein phosphatase inhibition. Eur J Neurosci 12: 2644 –2650,
2000.
343. Liao Y, Day KH, Damon DN, and Duling BR. Endothelial cellspecific knockout of connexin 43 causes hypotension and bradycardia in mice. Proc Natl Acad Sci USA 98: 9989 –9994, 2001.
344. Lin JS, Fitzgerald S, Dong Y, Knight C, Donaldson P, and
Kistler J. Processing of the gap junction protein connexin50 in the
ocular lens is accomplished by calpain. Eur J Cell Biol 73: 141–149,
1997.
345. Lin R, Warn-Cramer BJ, Kurata WE, and Lau AF. v-Src-mediated phosphorylation of connexin43 on tyrosine disrupts gap junctional communication in mammalian cells. Cell Commun Adhes 8:
265–269, 2001.
346. Little TL, Beyer EC, and Duling BR. Connexin43 and connexin40 gap junctional proteins are present in arteriolar smooth
muscle and endothelium in vivo. Am J Physiol Heart Circ Physiol
268: H729 –H739, 1995.
347. Little TL, Xia J, and Duling BR. Dye tracers define differential
endothelial and smooth muscle coupling patterns within the arteriolar wall. Circ Res 76: 498 –504, 1995.
348. Liu LW, Farraway L, Berezin I, and Huizinga JD. Interstitial
cells of Cajal: mediators of communication between circular and
longitudinal muscle layers of canine colon. Cell Tissue Res 294:
69 –79, 1998.
349. Liu TF and Johnson RG. Effects of TPA on dye transfer and dye
leakage in fibroblast transfected with a connexin 43 mutation at
ser368. Methods Find Exp Clin Pharmacol 21: 387–390, 1999.
350. Liu TF, Paulson AF, Li HY, Atkinson MM, and Johnson RG.
Inhibitory effects of 12-O-tetradecanoylphorbol-13-acetate on dye
leakage from single Novikoff cells and on dye transfer between
reaggregated cell pairs. Methods Find Exp Clin Pharmacol 19:
573–577, 1997.
351. Liu S, Taffet S, Stoner L, Delmar M, Vallano ML, and Jalife J.
A structural basis for the unequal sensitivity of the major cardiac
and liver gap junctions to intracellular acidification: the carboxyl
tail length. Biophys J 64: 1422–1433, 1993.
352. Lo CW. The role of gap junction membrane channels in development. J Bioenerg Biomembr 28: 379 –385, 1996.
353. Lo CW. Genes, gene knockouts, and mutations in the analysis of
gap junctions. Dev Genet 24: 1– 4, 1999.
354. Lo CW, Waldo KL, and Kirby ML. Gap junction communication
and the modulation of cardiac neural crest cells. Trends Cardiovasc Med 9: 63– 69, 1999.
355. Locke D, Perusinghe N, Newman T, Jayatilake H, Evans WH,
and Monaghan P. Developmental expression and assembly of
connexins into homomeric and heteromeric gap junction
hemichannels in the mouse mammary gland. J Cell Physiol 183:
228 –237, 2000.
356. Loewenstein WR and Kanno Y. Studies on an epithelial (gland)
cell junction. I. Modification of cell permeability. J Cell Biol 22:
565–586, 1964.
357. Loo LW, Berestecky JM, Kanemitsu MY, and Lau AF. pp60srcmediated phosphorylation of connexin 43, a gap junction protein.
J Biol Chem 270: 12751–12561, 1995.
358. Loo LW, Kanemitsu MY, and Lau AF. In vivo association of
pp60v-src and the gap-junction protein connexin 43 in v-src-transformed fibroblasts. Mol Carcinog 25: 187–195, 1999.
359. Lu C, Zhang H, Deng H, Xia K, Pan Q, and Xia J. Molecular
cloning of the human CX 58 gene. Zhonghua Yi Xue Yi Chuan Xue
Za Zhi 19: 95–99, 2002.
360. Luke RA and Saffitz JE. Remodeling of ventricular conduction
pathways in healed canine infarct border zones. J Clin Invest 87:
1594 –1602, 1991.
361. Mackay D, Ionides A, Berry V, Moore A, Bhattacharya S, and
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
319. Lamartine J, Munhoz Essenfelder G, Kibar Z, Lanneluc I,
Caallouet E, Laoudj D, Lemaitre G, Hand C, Hayflick SJ,
Zonana J, Aantonarakis S, Radhakrishma U, Kelsell DP,
Christianson AL, Pitaval A, Der Kaloustian V, Fraser C,
Blanchet-Bardon C, Rouleau GA, and Waksman G. Mutations
in GJB6 cause hidrotic ectodermal dysplasia. Nat Genet 26: 142–
144, 2000.
320. Lampe PD. Analyzing phorbol ester effects on gap junctional
communication: a dramatic inhibition of assembly. J Cell Biol 127:
1895–1905, 1994.
321. Lampe PD, Kurata WE, Warn-Cramer BJ, and Lau AF. Formation of a distinct connexin43 phosphoisoform in mitotic cells is
dependent upon p34cdc2 kinase. J Cell Sci 111: 833– 841, 1998.
322. Lampe PD and Lau AF. Regulation of gap junctions by phosphorylation of connexins. Arch Biochem Biophys 384: 205–215, 2000.
323. Lampe PD, TenBroek EM, Burt JM, Kurata WE, Johson RG,
and Lau AF. Phosphorylation of connexin43 on serine368 by
protein kinase C regulates gap junctional communication. J Cell
Biol 149: 1503–1512, 2000.
324. Landesman Y, White TW, Starich TA, Shaw JE, Goodenough
DA, and Paul DL. Innexin-3 forms connexin-like intercellular
channels. J Cell Sci 112: 2391–2396, 1999.
325. Larsen WJ. Biological implications of gap junction structure, distribution and composition: a review. Tissue Cell 15: 645– 671, 1983.
326. Larsen WJ and Tung HN. Origin and fate of cytoplasmic gap
junctional vesicles in rabbit granulosa cells. Tissue Cell 10: 585–
598, 1978.
327. Larsen WJ, Tung HN, Murray SA, and Swenson CA. Evidence
for the participation of actin microfilaments and bristle coats in the
internalization of gap junction membrane. J Cell Biol 83: 576 –587,
1979.
328. Larson DM, Seul KH, Berthoud VM, Lau AF, Sagar GD, and
Beyer EC. Functional expression and biochemical characterization of an epitope-tagged connexin37. Mol Cell Biol Res Commun 3:
115–121, 2000.
329. Larson DM and Sheridan JD. Junctional transfer in cultured
vascular endothelium. II. Dye and nucleotide transfer. J Membr
Biol 83: 157–167, 1985.
330. Lau AF, Kanemitsu MY, Kurata WE, Danesh AL, and Boynton
AK. Epidermal growth factor disrupts gap-junctional communication and induces phosphorylation of connexin43 on serine. Mol
Biol Cell 3: 865– 874, 1992.
331. Lauf U, Giepmans BN, Lopez P, Braconnot S, Chen SC, and
Falk MM. Dynamic trafficking and delivery of connexons to the
plasma membrane and accretion to gap junctions in living cells.
Proc Natl Acad Sci USA 99: 10446 –10451, 2002.
332. Lautermann J, ten Cate WJ, Altenhoff P, Grummer R, Traub
O, Frank H, Jahnke K, and Winterhager E. Expression of the
gap-junction connexins 26 and 30 in the rat cochlea. Cell Tissue Res
294: 415– 420, 1998.
333. Lawrence TS, Beers WH, and Gilula NB. Transmission of hormonal stimulation by cell-to-cell communication. Nature 272: 501–
506, 1978.
334. Lee SM and Clemens MG. Subacinar distribution of hepatocyte
membrane potential response to stimulation of gluconeogenesis.
Am J Physiol Gastrointest Liver Physiol 263: G319 –G326, 1992.
335. Lefebvre PP and van de Water TR. Connexins, hearing and
deafness: clinical aspects of mutations in the connexin 26 gene.
Brain Res Rev 32: 159 –162, 2000.
336. Leite MF, Hirata K, Pusl T, Burgstahler AD, Okazaki K, Ortega JM, Goes AM, Prado MA, Spray DC, and Nathanson MH.
Molecular basis for pacemaker cells in epithelia. J Biol Chem 277:
16313–16323, 2002.
337. Leube RE. The topogenic fate of the polytopic transmembrane
proteins, synaptophysin and connexin, is determined by their membrane-spanning domains. J Cell Sci 108: 883– 894, 1995.
338. Levin M. Isolation and community: a review of the role of gapjunctional communication in embryonic patterning. J Membr Biol
185: 177–192, 2002.
339. Li F, Sugishita K, Su Z, Ueda I, and Barry WH. Activation of
connexin-43 hemichannels can elevate [Ca2⫹]i and [Na⫹]i in rabbit
ventricular myocytes during metabolic inhibition. J Mol Cell Cardiol 33: 2145–2155, 2001.
CONNEXIN CHANNELS
362.
363.
364.
365.
366.
367.
369.
370.
371.
372.
373.
374.
375.
376.
377.
378.
379.
380.
381.
382.
Physiol Rev • VOL
383. Mine T, Yusuda H, Kataoka A, Tajima A, Nagasawa J, and
Takano T. Human chronic gastric ulcer and connexin. J Clin
Gastroenterol 21: S104 –S107, 1995.
384. Minkoff R, Rundus VR, Parker SB, Beyer EC, and Hertzberg
EL. Connexin expression in the developing avian cardiovascular
system. Circ Res 73: 71–78, 1993.
385. Moennikes O, Buchmann A, Ott T, Willecke K, and Schwarz
M. The effect of connexin32 null mutation on hepatocarcinogenesis in different mouse strains. Carcinogenesis 20: 1379 –1382,
1999.
386. Mok BW, Yeung WS, and Luk JM. Differential expression of
gap-junction gene connexin 31 in seminiferous epithelium of rat
testes. FEBS Lett 453: 243–248, 1999.
387. Montecino-Rodrı́guez E and Dorshkind K. Regulation of hematopoiesis by gap junction-mediated intercellular communication.
J Leukoc Biol 70: 341–347, 2001.
388. Moorby CD and Gherardi E. Expression of a Cx43 deletion
mutant in 3T3 A31 fibroblasts prevents PDGF-induced inhibition of
cell communication and suppresses cell growth. Exp Cell Res 249:
367–376, 1999.
389. Moreno AP, Campos de Carvalho AC, Verselis V, Eghbali B,
and Spray DC. Voltage-dependent gap junction channels are
formed by connexin32, the major gap junction protein of rat liver.
Biophys J 59: 920 –925, 1991.
390. Moreno AP, Fishman GI, and Spray DC. Phosphorylation shifts
unitary conductance and modifies voltage dependent kinetics of
human connexin43 gap junction channels. Biophys J 62: 51–53,
1992.
391. Moreno AP, Laing JG, Beyer EC, and Spray DC. Properties of
gap junction channels formed of connexin 45 endogenously expressed in human hepatoma (SKHep1) cells. Am J Physiol Cell
Physiol 268: C356 –C365, 1995.
392. Morle L, Bozon M, Alloisio N, Latour P, Vanderberghe A,
Plauchu H, Collet L, Edery P, Godet J, and Lina-Granade G. A
novel C202F mutation in the connexin26 gene (GJB2) associated
with autosomal dominant isolated hearing loss. J Med Genet 37:
368 –370, 2000.
393. Motoyama K, Karl IE, Flye MW, Osborne DF, and Hotchkiss
RS. Effect of Ca2⫹ agonists in the perfused liver: determination via
laser scanning confocal microscopy. Am J Physiol Regul Integr
Comp Physiol 276: R575–R585, 1999.
394. Muller DJ, Hand GM, Engel A, and Sosinsky GE. Conformational changes in surface structures of isolated connexin 26 gap
junctions. EMBO J 21: 3598 –3607, 2002.
395. Munari-Silem Y and Rousset B. Gap junction-mediated cell-tocell communication in endocrine glands. Molecular and functional
aspects: a review. Eur J Endocrinol 135: 251–264, 1996.
396. Muramatsu T, Hashimoto S, and Shimono M. Differential expression of gap junction proteins connexin32 and 43 in rat submandibular and sublingual glands. J Histochem Cytochem 44: 49 –56,
1996.
397. Murray SA, Larsen WJ, Trout J, and Donta ST. Gap junction
assembly and endocytosis correlated with patterns of growth in a
cultured adrenocortical tumor cell (SW-13). Cancer Res 41: 4063–
4074, 1981.
398. Murray SA, Williams SY, Dillard CY, Narayanan SK, and McCauley J. Relationship of cytoskeletal filaments to annular gap
junction expression in human adrenal cortical tumor cells in culture. Exp Cell Res 234: 398 – 404, 1997.
399. Musil LS, Beyer EC, and Goodenough DA. Expression of the
gap junction protein connexin43 in embryonic chick lens: molecular cloning, ultrastructural localization, and post-translational
phosphorylation. J Membr Biol 116: 163–175, 1990.
400. Musil LS, Cunningham BA, Edelman GM, and Goodenough
DA. Differential phosphorylation of the gap junction protein connexin43 in junctional communication-competent and -deficient cell
lines. J Cell Biol 111: 2077–2088, 1990.
401. Musil LS and Goodenough DA. Biochemical analysis of connexin43 intracellular transport, phosphorylation, and assembly into
gap junctional plaques. J Cell Biol 115: 1357–1374, 1991.
402. Musil LS and Goodenough DA. Multisubunit assembly of an
integral plasma membrane channel protein, gap junction connexin43, occurs after exit from the ER. Cell 74: 1065–1077, 1993.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
368.
Shiels A. A new locus for dominat “zonular pulverulent” cataract,
on chromosome 13. Am J Hum Genet 60: 1474 –1478, 1997.
Makowski L, Caspar DLD, Phillips WC, and Goodenough DA.
Gap junction structures. II. Analysis of the X-ray diffraction data.
J Cell Biol 74: 629 – 645, 1977.
Malchow RP, Quian H, and Ripps H. A novel action of quinine
and quinidine on the membrane conductance of neurons from the
vertebrate retina. J Gen Physiol 104: 1039 –1055, 1994.
Mambetisaeva ET, Gire V, and Evans WH. Multiple connexin
expression in peripheral nerve, Schwann cells, and Schwannoma
cells. J Neurosci Res 57: 166 –175, 1999.
Manjunath CK, Goings GE, and Page E. Cytoplasmic surface
and intramembrane components of rat heart gap junctional proteins. Am J Physiol Heart Circ Physiol 246: H865–H875, 1984.
Manjunath CK, Goings GE, and Page E. Proteolysis of cardiac
gap junctions during their isolation from rat hearts. J Membr Biol
85: 159 –168, 1985.
Manthey D, Banach K, Desplantez T, Lee CG, Kozak CA,
Traub O, Weingart R, and Willecke K. Intracellular domains of
mouse connexin26 and -30 affect diffusional and electrical properties of gap junction channels. J Membr Biol 181: 137–148, 2001.
Manthey D, Bukauskas F, Lee CG, Kozak CA, and Willecke K.
Molecular cloning and functional expression of the mouse gap
junction gene connexin-57 in human HeLa cells. J Biol Chem 274:
14716 –14723, 1999.
Martin CA, Homaidan FR, Palaia T, Burakoff R, and El-Sabban ME. Gap junctional communication between murine macrophages and intestinal epithelial cell lines. Cell Commun Adhes 5:
437– 449, 1998.
Martin PE, Blundell G, Ahmad S, Errington RJ, and Evans
WH. Multiple pathways in the trafficking and assembly of connexin
26, 32 and 43 into gap junction intercellular communication channels. J Cell Sci 114: 3845–3855, 2001.
Martı́nez AD, Eugenı́n EA, Brañes MC, Bennett MV, and Sáez
JC. Identification of second messengers that induce expression of
functional gap junctions in microglia cultured from newborn rats.
Brain Res 943: 191–201, 2002.
Martı́nez AD, Hayrapetyan V, Moreno AP, and Beyer EC.
Connexin43 and connexin45 form heteromeric gap junction channels in which individual components determine permeability and
regulation. Circ Res 90: 1100 –1107, 2002.
Mathias RT, Rae JL, and Baldo GJ. Physiological properties of
the normal lens. Physiol Rev 77: 21–50, 1997.
Mayerhofer A and Garfield RE. Immunocytochemical analysis of
the expression of gap junction protein connexin 43 in the rat ovary.
Mol Reprod Dev 41: 331–338, 1995.
Mazet F, Wittenberg BA, and Spray DC. Fate of intercellular
junctions in isolated adult rat cardiac cells. Circ Res 56: 195–204,
1985.
McGrew LL, Takemaru K, Bates R, and Moon RT. Direct regulation of the Xenopus engrailed-2 promoter by the Wnt signaling
pathway, and a molecular screen for Wnt-responsive genes, confirm a role for Wnt signaling during neural patterning in Xenopus.
Mech Dev 87: 21–32, 1999.
Meda P. Gap junction involvement in secretion: the pancreas
experience. Clin Exp Pharmacol Physiol 23: 1053–1057, 1996.
Meda P, Bruzzone R, Knodel S, and Orci L. Blockage of cell-tocell communication within pancreatic acini is associated with increased basal release of amylase. J Cell Biol 103: 475– 483, 1986.
Meda P, Pepper MS, Traub O, Willecke K, Gros D, Beyer E,
Nicholson B, Paul D, and Orci L. Differential expression of gap
junction connexins in endocrine and exocrine glands. Endocrinology 133: 2371–2378, 1993.
Mehta PP, Yamamoto M, and Rose B. Transcription of the gene
for the gap junctional protein connexin43 and expression of functional cell-to-cell channels are regulated by cAMP. Mol Biol Cell 3:
839 – 850, 1992.
Meyer RA, Laird DW, Revel JP, and Johnson RG. Inhibition of
gap junction and adherens junction assembly by connexin and
A-CAM antibodies. J Cell Biol 119: 179 –189, 1992.
Milks LC, Kumar NM, Houghten R, Unwin N, and Gilula NB.
Topology of the 32-kD liver gap junction protein determined by site
directed antibody localizations. EMBO J 7: 2967–2975, 1988.
1393
1394
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
423.
424.
425.
426.
427.
428.
429.
430.
431.
432.
433.
434.
435.
436.
437.
438.
439.
440.
441.
tional protein expressed preferentially in the skate retina. Mol Biol
Cell 7: 233–243, 1996.
O’Brien J, Bruzzone R, White TW, Al-Ubaidi MR, and Ripps H.
Cloning and expression of two related connexins from the perch
retina define a distinct subgroup of the connexin family. J Neurosci
18: 7625–7637, 1998.
Oesterle EC and Dallos P. Intracellular recordings from supporting cells in the guinea pig cochlea: DC potencials. J Neurophysiol
64: 617– 636, 1990.
Oh S, Ri Y, Bennett MV, Trexler EB, Verselis VK, and Bargiello TA. Changes in permeability caused by connexin 32 mutations underlie X-linked Charcot-Marie-Tooth disease. Neuron 19:
927–938, 1997.
Oh SY, Grupen CG, and Murray AW. Phorbol ester induces
phosphorylation and down-regulation of connexin 43 in WB cells.
Biochim Biophys Acta 1094: 243–245, 1991.
Ohkusa T, Fujiki K, Tamura Y, Yamamoto M, and Kyoi T.
Freeze-fracture and immunohistochemical studies of gap junctions
in human gastric mucosa with special reference to their relationship to gastric ulcer and gastric carcinoma. Microsc Res Tech 31:
226 –233, 1995.
Okuma A, Kuraoka A, Iida H, Inai T, Wasano K, and Shibata
Y. Colocalization of connexin 43 and connexin 45 but absence of
connexin 40 in granulosa cell gap junctions of rat ovary. J Reprod
Fertil 107: 255–264, 1996.
Omori Y, Mesnil M, and Yamasaki H. Connexin 32 mutations
from X-linked Charcot-Marie-Tooth disease patients: functional defects and dominant negative effects. Mol Biol Cell 7: 907–916, 1996.
Oosthoek PW, Viragh S, Lamers WH, and Moorman AFM.
Immunohistochemical delineation of the conduction system. II.
The atrioventricular node and the Purkinje fibers. Circ Res 73:
482– 491, 1993.
Oosthoek PW, Viragh S, Mayen AEM, van Kempen MJA, Lamers WH, and Moorman AFM. Immunohistochemical delineation
of the conduction system. I. The sinoatrial node. Circ Res 73:
473– 481, 1993.
Orkand RK, Nicholls JG, and Kuffler SWK. Effect of nerve
impulses on the membrane potential of glial cells in the central
nervous system of amphibia. J Neurophysiol 29: 788 – 806, 1966.
Orsino A, Taylor CV, and Lye SJ. Connexin-26 and connexin43
are differentially expressed and regulated in the rat myometrium
throughout late pregnancy and with the onset of labor. Endocrinology 137: 1545–1553, 1996.
Oviedo-Orta E, Errington RJ, and Evans WH. Gap junction
intercellular communication during lymphocyte transendothelial
migration. Cell Biol Int 26: 253–263, 2002.
Oviedo-Orta E, Gasque P, and Evans WH. Immunoglobulin and
cytokine expression in mixed lymphocyte cultures is reduced by
disruption of gap junction intercellular communication. FASEB J
15: 768 –774, 2001.
Oviedo-Orta E, Hoy T, and Evans WH. Intercellular communication in the immune system: differential expression of connexin40
and 43, and perturbation of gap junction channel functions in
peripheral blood and tonsil human lymphocyte subpopulations.
Immunology 99: 578 –590, 2000.
Pal JD, Berthoud VM, Beyer EC, Mackay D, Shiels A, and
Ebihara L. Molecular mechanism underlying a Cx50-linked congenital cataract. Am J Physiol Cell Physiol 276: C1443–C1446, 1999.
Pal JD, Liu X, Mackay D, Shiels A, Berthoud VM, Beyer EC
and Ebihara L. Connexin46 mutations linked to congenital cataract show loss of gap junction channel function. Am J Physiol Cell
Physiol 279: C596 –C602, 2000.
Panchin Y, Kelmanson I, Matz M, Lukyanov K, Usman N, and
Lukyanov S. A ubiquitous family of putative gap junction molecules. Curr Biol 29: R473–R474, 2000.
Pappas GD, Asada Y, and Bennett MVL. Morphological correlates of increased coupling resistance at an electrotonic synapse.
J Cell Biol 49: 173–188, 1971.
Pauken CM and Lo CW. Nonoverlapping expression of Cx43 and
Cx26 in the mouse placenta and decidua: a pattern of gap junction
gene expression differing from that in the rat. Mol Reprod Dev 41:
195–203, 1995.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
403. Musso M, Balestra P, Bellone E, Cassandrini D, Di Maria E,
Doria LL, Grandis M, Mancardi GL, Schenone A, Levi G,
Ajmar and Mandich PF. The D355V mutation decreases EGR2
binding to an element within the Cx32 promoter. Neurobiol Dis 8:
700 –706, 2001.
404. Nagy JI, Li X, Rempel J, Stelmack G, Patel D, Staines WA,
Yasumura T, and Rash JE. Connexin26 in adult rodent central
nervous system: demonstration at astrocytic gap junctions and
colocalization with connexin30 and connexin43. J Comp Neurol
441: 302–323, 2001.
405. Nakamura K, Kuraoka A, Kawabuchi M, and Shibata Y. Specific localization of gap junction protein, connexin45, in the deep
muscular plexus of dog and rat small intestine. Cell Tissue Res 292:
487– 494, 1998.
406. Nathanson M, Burgstahler AD, Mennone A, Fallon MB,
González CB, and Sáez JC. Ca2⫹ waves are organized among
hepatocytes in the intact organ. Am J Physiol Gastrointest Liver
Physiol 269: G167–G171, 1995.
407. Nathanson MH, Rı́os-Vélez L, Burgstahler AD, and Mennone
A. Communication via gap junctions modulates bile secretion in
the isolated perfused rat liver. Gastroenterology 116: 1176 –1183,
1999.
408. Naus CC, Hearn S, Zhu D, Nicholson BJ, and Shivers RR.
Ultrastructural analysis of gap junctions in C6 glioma cells transfected with connexin43 cDNA. Exp Cell Res 206: 72– 84, 1993.
409. Nelles E, Bützler C, Jung D, Temme A, Gabriel HD, Dahl U,
Traub O, Stümpel F, Jungermann K, Zielasek J, Toyka KV,
Dermietzel R, and Willecke K. Defective propagation of signals
generated by sympathetic nerve stimulation in the liver of conexin32-deficient mice. Proc Natl Acad Sci USA 93: 9565–9570, 1996.
410. Nemeth L, Maddur S, and Puri P. Immunolocalization of the gap
junction protein Connexin43 in the interstitial cells of Cajal in the
normal and Hirschsprung’s disease bowel. J Pediatr Surg 35: 823–
828, 2000.
411. Neuhaus IM, Bone L, Wang S, Ionasescu V, and Werner R. The
human connexin32 gene is transcribed from two tissue-specific
promoters. Biosci Rep 16: 239 –248, 1996.
412. Ngezahayo A, Zeilinger C, Todt II, Marten II, and Kolb H.
Inactivation of expressed and conducting rCx46 hemichannels by
phosphorylation. Pflügers Arch 436: 627– 629, 1998.
413. Nicholson BJ, Dermietzel R, Teplow D, Traub O, Willecke K,
and Revel JPP. Two homologous protein components of hepatic
gap junctions. Nature 329: 732–734, 1987.
414. Nicholson BJ, Gros DB, Kent SB, Hood LE, and Revel JP. The
Mr 28,000 gap junction proteins from rat heart and liver are different but related. J Biol Chem 260: 6514 – 6517, 1985.
415. Nicholson SM, Gomes D, De Nechaud B, and Bruzzone R.
Altered gene expression in Schwann cells of connexin32 knockout
animals. J Neurosci Res 66: 23–36, 2001.
416. Nielsen PA, Baruch A, Giepmans BN, and Kumar NM. Characterization of the association of connexins and ZO-1 in the lens. Cell
Commun Adhes 8: 213–217, 2001.
417. Nielsen PA, Beahm DL, Giepmans BN, Baruch A, Hall JE, and
Kumar NM. Molecular cloning, functional expression, and tissue
distribution of a novel human gap junction forming protein, connexin-31.9. Interaction with zona occludens protein-1. J Biol Chem
277: 38272–38283, 2002.
418. Niessen H, Harz H, Bedner P, Kramer K, and Willecke K.
Selective permeability of different connexin channels to the second
messenger inositol 1,4,5-trisphosphate. J Cell Sci 113: 1365–1372,
2000.
419. Niessen H and Willecke K. Strongly decreased gap junctional
permeability to inositol 1,4,5-trisphosphate in connexin32 deficient
hepatocytes. FEBS Lett 466: 112–114, 2000.
420. Nishii K, Kumai M, and Shibata Y. Regulation of the epithelialmesenchymal transformation through gap junction channels in
heart development. Trends Cardiovasc Med 11: 213–218, 2001.
421. Nuttinck F, Peynot N, Humblot P, Massip A, Dessy F, and
Flechon JE. Comparative immunohistochemical distribution of
connexin 37 and connexin 43 throughout folliculogenesis in the
bovine ovary. Mol Reprod Dev 57: 60 – 66, 2000.
422. O’Brien J, Al-Ubaidi MR, and Ripps H. Connexin35: a gap junc-
CONNEXIN CHANNELS
Physiol Rev • VOL
465.
466.
467.
468.
469.
470.
471.
472.
473.
474.
475.
476.
477.
478.
479.
480.
481.
482.
483.
484.
gene expression in the rabbit arterial wall: effects of hypercholesterolemia, balloon injury and their combination. J Vasc Res 34:
19 –30, 1997.
Polacek D, Lal R, Volin MV, and Davies PF. Gap junctional
communication between vascular cells. Induction of connexin43
messenger RNA in macrophage foam cells of atherosclerotic lesions. Am J Pathol 142: 593– 606, 1993.
Postma FR, Hengeveld T, Alblas J, Giepmans BN, Zondag GC,
Jalink K, and Moolenaar WH. Acute loss of cell-cell communication caused by G protein-coupled receptors: a critical role for
c-Src. J Cell Biol 140: 1199 –1209, 1998.
Potenza N, del Gaudio R, Rivieccio L, Russo GM, and Geraci
G. Cloning and molecular characterization of the first innexin of
the phylum annelida-expression of the gene during development. J
Mol Evol 54: 312–321, 2002.
Potter DD, Furshpan EJ, and Lennox ES. Connections between
cells of the developing squid as revealed by electrophysiological
methods. Proc Natl Acad Sci USA 55: 328 –336, 1966.
Proulx A, Merrifield PA, and Naus CC. Blocking gap junctional
intercellular communication in myoblasts inhibits myogenin and
MRF4 expression. Dev Genet 20: 133–144, 1997.
Puranam KL, Laird DW, and Revel JP. Trapping an intermediate
form of connexin43 in the Golgi. Exp Cell Res 206: 85–92, 1993.
Quist AP, Rhee SK, Lin H, and Lal R. Physiological role of
gap-junctional hemichannels. Extracellular calcium-dependent
isosmotic volume regulation. J Cell Biol 148: 1063–1074, 2000.
Radebold K, Horakova E, Gloeckner J, Ortega G, Spray DC,
Vieweger H, Siebert K, Manuelidis L, and Geibel JP. Gap
junctional channels regulate acid secretion in the mammalian gastric gland. J Membr Biol 183: 147–153, 2001.
Rae JL, Bartling C, Rae J, and Mathias RT. Dye transfer between cells of the lens. J Membr Biol 150: 89 –103, 1996.
Rahman S, Carlile G, and Evans WH. Assembly of hepatic gap
junctions. Topography and distribution of connexin 32 in intracellular and plasma membranes determined using sequence-specific
antibodies. J Biol Chem 268: 1260 –1265, 1993.
Rahman S and Evans WH. Topography of connexin32 in rat liver
gap junctions. Evidence for an intramolecular disulfide linkage
connecting the two extracellular peptide loops. J Cell Sci 100:
567–578, 1991.
Rash JE and Yasumura T. Direct immunogold labeling of connexins and aquaporin-4 in freeze-fracture replicas of liver, brain,
and spinal cord: factors limiting quantitative analysis. Cell Tissue
Res 296: 307–321, 1999.
Reaume AG, de Sousa PA, Kulkarni S, Langille BL, Zhu D,
Davies TC, Juneja SC, Kidder GM, and Rossant J. Cardiac
malformation in neonatal mice lacking connexin43. Science 267:
1831–1834, 1995.
Reed KE, Westphale EM, Larson DM, Wang HZ, Veenstra RD,
and Beyer EC. Molecular cloning and functional expression of
human connexin37, an endothelial cell gap junction protein. J Clin
Invest 91: 997–1004, 1993.
Ren P, de Feijter AW, Paul DL, and Ruch RJ. Enhancement of
liver cell gap junction protein expression by glucocorticoids. Carcinogenesis 15: 1807–1813, 1994.
Ressot C, Gomes D, Dautigny A, Pham-Dinh D, and Bruzzone
R. Connexin32 mutations associated with X-linked Charcot-MarieTooth disease show two distinct behaviors: loss of function and
altered gating properties. J Neurosci 18: 4063– 4075, 1998.
Revel JP and Karnovsky MJ. Hexagonal array of subunits in
intercellular junctions of the mouse heart and liver. J Cell Biol 33:
C7–C12, 1967.
Revel JP, Yee AG, and Hudspeth AJ. Gap junctions between
electrotonically coupled cells in tissue culture and in brown fat.
Proc Natl Acad Sci USA 68: 2924 –2927, 1971.
Richard G, Smith LE, Bailey RA, Itin P, Hohl D, Epstein EH
Jr, DiGiovanna JJ, Compton JG, and Bale SJ. Mutations in the
human connexin gene GJB3 cause erythrokeratodermia variabilis.
Nat Genet 20, 366 –369, 1998.
Richard G, White TW, Smith LE, Bailey RA, Compton JG, Paul
DL, and Bale SJ. Functional defects of Cx26 resulting from a
heterozygous missense mutation in a family with dominant deaf-
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
442. Paul DL. Molecular cloning of cDNA for rat liver gap junction.
J Cell Biol 103: 123–134, 1986.
443. Paul DL. New functions for gap junctions. Curr Opin Cell Biol 7:
665– 672, 1995.
444. Paul DL, Ebihara L, Takemoto LJ, Swenson KI, and Goodenough DA. Connexin46, a novel lens gap junction protein, induces voltage-gated currents in nonjunctional plasma membrane of
Xenopus oocytes. J Cell Biol 115: 1077–1089, 1991.
445. Paulson AF, Lampe PD, Meyer RA, TenBroek E, Atkinson
MM, Walseth TF, and Johnson RG. Cyclic AMP and LDL trigger
a rapid enhancement in gap junction assembly through a stimulation of connexin trafficking. J Cell Sci 113: 3037–3049, 2000.
446. Paznekas WA, Boyadjiev SA, Shapiro RE, Daniels O, Wollnik
B, Keegan CE, Innis JW, Dinulos MB, Christian C, Hannibal
MC, and Jabs EW. Connexin 43 (GJA1) mutations cause the
pleiotropic phenotype of oculodentodigital dysplasia. Am J Hum
Genet 72: 408 – 418, 2003.
447. Pelletier RM. Cyclic modulation of Sertoli cell junctional complexes in a seasonal breeder: the mink (Mustela vison). Am J Anat
183: 68 –102, 1988.
448. Pelletier RM. The distribution of connexin 43 is associated with
the germ cell differentiation and with the modulation of the Sertoli
cell junctional barrier in continual (guinea pig) and seasonal breeders’ (mink) testes. J Androl 16: 400 – 409, 1995.
449. Pelletier DB and Boynton AL. Dissociation of PDGF receptor
tyrosine kinase activity from PDGF-mediated inhibition of gap
junctional communication. J Cell Physiol 158: 427– 434, 1994.
450. Pérez-Armendáriz EM, Lamoyi E, Mason JI, Cisneros-Armas
D, Luu-The V, and Bravo Moreno JF. Developmental regulation
of connexin 43 expression in fetal mouse testicular cells. Anat Rec
264: 237–246, 2001.
451. Perkins GA, Goodenough DA, and Sosinsky GE. Formation of
the gap junction intercellular channel requires a 30 degree rotation
for interdigitating two apposing connexons. J Mol Biol 277: 171–
177, 1998.
452. Peters NS. Myocardial gap junction organization in ischemia and
infarction. Microsc Res Tech 31: 375–386, 1995.
453. Pfahnl A and Dahl G. Localization of a voltage gate in connexin46
gap junction hemichannels. Biophys J 75: 2323–2331, 1998.
454. Pfahnl A and Dahl G. Gating of cx46 gap junction hemichannels
by calcium and voltage. Pflügers Arch 437: 345–353, 1999.
455. Pfahnl A, Zhou XW, Werner R, and Dahl G. A chimeric connexin
forming gap junction hemichannels. Pflügers Arch 433: 773–779,
1997.
456. Phelan P, Bacon JP, Davies JA, Stebbings LA, Todman MG,
Avery L, Baines RA, Barnes TM, Ford C, Hekimi S, Lee R,
Shaw JE, Starich TA, Curtin KD, Sun YA, and Wyman RJ.
Innexins: a family of invertebrate gap-junction proteins. Trends
Genet 14: 348 –349, 1998.
457. Phelan P and Starich TA. Innexins get into the gap. Bioessays 23:
388 –396, 2001.
458. Phelan P, Stebbings LA, Baines RA, Bacon JP, Davies JB, and
Ford C. Drosophila Shaking-B proteins forms gap junctions in
paired Xenopus oocytes. Nature 391: 181–184, 1998.
459. Piechocki MP, Burk RD, and Ruch RJ. Regulation of connexin32
and connexin43 gene expression by DNA methylation in rat liver
cells. Carcinogenesis 20: 401– 406, 1999.
460. Piersanti M and Lye SJ. Increase in messenger ribonucleic acid
encoding the myometrial gap junction protein, connexin-43, requires protein synthesis and is associated with increased expression of the activator protein-1, c-fos. Endocrinology 136: 3571–
3578, 1995.
461. Pinero GJ, Parker S, Rundus V, Hertzberg EL, and Minkoff R.
Immunolocalization of connexin 43 in the tooth germ of the neonatal rat. Histochem J 26: 765–770, 1994.
462. Plotkin LI, Manolagas SC, and Bellido T. Transduction of cell
survival signals by connexin-43 hemichannels. J Biol Chem 277:
8648 – 8657, 2002.
463. Plum A, Hallas G, Magin T, Dombrowski F, Hagendorff A,
Schumacher B, Wolpert C, Kim J, Lamers WH, Evert M, Meda
P, Traub O, and Willecke K. Unique and shared functions of
different connexins in mice. Curr Biol 10: 1083–1091, 2000.
464. Polacek D, Bech F, McKinsey JF, and Davies PF. Connexin43
1395
1396
485.
486.
487.
488.
489.
490.
492.
493.
494.
495.
496.
497.
498.
499.
500.
501.
502.
503.
504.
505.
mutism and palmoplantar keratoderma. Hum Genet 103: 393–399,
1998.
Risek B and Gilula NB. Spatiotemporal expression of three gap
junction gene products involved in fetomaternal communication
during rat pregnancy. Development 113: 165–181, 1991.
Risek B, Guthrie S, Kumar N, and Gilula NB. Modulation of gap
junction transcript and protein expression during pregnancy in the
rat. J Cell Biol 110: 269 –282, 1990.
Risek B, Klier FG, Phillips A, Hahn DW, and Gilula NB. Gap
junction regulation in the uterus and ovaries of immature rats by
estrogen and progesterone. J Cell Sci 108: 1017–1032, 1995.
Risley MS. Connexin gene expression in seminiferous tubules of
the Sprague-Dawley rat. Biol Reprod 62: 748 –754, 2000.
Risley MS, Tan IP, Roy C, and Sáez JC. Cell-, age- and stagedependent distribution of connexin43 gap junctions in testes. J Cell
Sci 103: 81–96, 1992.
Robb-Gaspers LD and Thomas AP. Coordination of Ca2⫹ signaling by intercellular propagation of Ca2⫹ waves in the intact liver.
J Biol Chem 270: 8102– 8107, 1995.
Robertson JD. The occurrence of a subunit pattern in the unit
membranes of the club endings in Mauthner cell synapses in goldfish brains. J Cell Biol 19: 201–221, 1963.
Romanello M and D’Andrea P. Dual mechanism of intercellular
communication in HOBIT osteoblastic cells: a role for gap-junctional hemichannels. J Bone Miner Res 16: 1465–1476, 2001.
Rong P, Wang X, Niesman I, Wu Y, Benedetti LE, Dunia I, Levy
E, and Gong X. Disruption of Gja8 (alpha8 connexin) in mice leads
to microphthalmia associated with retardation of lens growth and
lens fiber maturation. Development 129: 167–174, 2002.
Roscoe WA, Barr KJ, Mhawi AA, Pomerantz DK, and Kidder
GM. Failure of spermatogenesis in mice lacking connexin43. Biol
Reprod 65: 829 – 838, 2001.
Rosendaal M, Green CR, Rahman A, and Morgan D. Up-regulation of the connexin43⫹ gap junction network in haemopoietic
tissue before the growth of stem cells. J Cell Sci 107: 29 –37, 1994.
Rosendaal M and Jopling C. Hemopoietic capacity of connexin43
wild-type and knock-out fetal liver cells not different on wild type
stroma. Blood 101: 2996 –2998, 2003.
Rosendaal M and Krenacs TT. Regulatory pathways in bloodforming tissue with particular reference to gap junctional communication. Pathol Oncol Res 6: 243–249, 2000.
Rouan F, White TW, Brown N, Taylor AM, Lucke TW, Paul DL,
Munro CS, Uitto J, Hodgins MB, and Richard G.. Trans-dominant inhibition of connexin-43 by mutant connexin-26: implications
for dominant connexin disorders affecting epidermal differentiation. J Cell Sci 114: 2105–2113, 2001.
Rozental R, Srinivas M, and Spray DC. How to close a gap
junction channel. Efficacies and potencies of uncoupling agents.
Methods Mol Biol 154: 447– 476, 2001.
Rup DM, Veenstra RD, Wang HZ, Brink PR, and Beyer EC.
Chick connexin-56, a novel lens gap junction protein. Molecular
cloning and functional expression. J Biol Chem 268: 706 –712, 1993.
Rutz ML and Hülser DF. Supramolecular dynamics of gap junctions. Eur J Cell Biol 80: 20 –30, 2001.
Sáez JC, Araya R, Brañes MC, Concha M, Contreras JE,
Eugenı́n EA, Martı́nez AD, Palisson F, and Sepúlveda MA.
Gap junctions in inflammatory responses: connexins, regulation
and possible functional roles. In: Current Topics in Membranes.
Molecular Basis of Cell Communication in Health and Disease,
edited by Perrachia C. San Diego: Academic, 2000, vol 49, p. 555–
579.
Sáez JC, Brañes MC, Corvalán LA, Eugenı́n EA, González H,
Martı́nez AD, and Palisson F. Gap junctions in cells of the
immune system: structure, regulation and possible functional roles.
Braz J Med Biol Res 33: 447– 455, 2000.
Sáez JC, Connor JA, Spray DC, and Bennett MVL. Hepatocyte
gap junctions are permeable to the second messenger inositol
1,4,5-trisphosphate and calcium ions. Proc Natl Acad Sci USA 86:
2708 –2712, 1989.
Sáez JC, Gregory WA, Watanabe T, Dermietzel R, Hertzberg
EL, Reid L, Bennett MVL, and Spray DC. cAMP delays disappearance of gap junctions between pairs of rat hepatocytes in
primary culture. Am J Physiol Cell Physiol 257: C1–C11, 1989.
Physiol Rev • VOL
506. Sáez JC, Martı́nez AD, Brañes MC, and González HE. Regulation of gap junctions by protein phosphorylation. Braz J Med Biol
Res 31: 593– 600, 1998.
507. Sáez JC, Nairn AC, Czernik AJ, Fishman GI, Spray DC, and
Hertzberg EL. Phosphorylation of connexin43 and the regulation
of neonatal rat cardiac myocyte gap junctions. J Mol Cell Cardiol
29: 2131–2145, 1997.
508. Sáez JC, Nairn AC, Czernik AJ, Spray DC, Hertzberg EL,
Greengard P, and Bennett MV. Phosphorylation of connexin 32,
a hepatocyte gap-junction protein, by cAMP-dependent protein
kinase, protein kinase C and Ca2⫹/calmodulin-dependent protein
kinase II. Eur J Biochem 192: 263–273, 1990.
509. Sáez JC, Nairn AC, Czernik AJ, Spray DC, and Hertzberg EL.
Rat heart connexin43: regulation by phosphorylation in heart. Gap
junctions. In: Progress in Cell Research, Gap Junctions, edited by
Hall JE, Zampighi GA, and Davis RM. Amsterdam: Elsevier Science,
1993, vol. 39, p. 263–269.
510. Sáez JC, Sepúlveda MA, Araya R, Sáez CG, and Palisson F.
Concanavalin A-activated lymphocytes form gap junctions that
increase their rate of DNA replication. In: Gap Junctions, edited by
Werner R. Amsterdam: IOS, 1998, p. 372–381.
511. Sáez JC, Spray DC, Nairn AC, Hertzberg E, Greengard P, and
Bennett MV. cAMP increases junctional conductance and stimulates phosphorylation of the 27-kDa principal gap junction polypeptide. Proc Natl Acad Sci USA 83: 2473–2477, 1986.
512. Saffitz JE, Kanter HL, Green KG, Tolley TK, and Beyer EC.
Tissue-specific determinants of anisotropic conduction velocity in
canine atrial and ventricular myocardium. Circ Res 74: 1065–1070,
1994.
513. Saitoh M, Oyamada M, Oyamada Y, Kaku T, and Mori M.
Changes in the expression of gap junction proteins (connexins) in
hamster tongue epithelium during wound healing and carcinogenesis. Carcinogenesis 18: 1319 –1328, 1997.
514. Saleh SM, Takemoto LJ, Zoukhri D, and Takemoto DJ. PKCgamma phosphorylation of connexin 46 in the lens cortex. Mol Vis
7: 240 –246, 2001.
515. Sasaki T and Garant PR. Fate of annular gap junctions in the
papillary cells of the enamel organ in the rat incisor. Cell Tissue
Res 246: 523–530, 1986.
516. Scherer SS, Deschenes SM, Xu YT, Grinspan JB, Fischbeck
KH, and Paul DL. Conexin32 is a myelin-related protein in the
PNS and CNS. J Neurosci 15: 8281– 8294, 1995.
517. Scherer SS, Xu YT, Nelles E, Fischbeck K, Willecke K, and
Bone LJ. Connexin32-null mice develop demyelinating peripheral
neuropathy. Glia 24: 8 –20, 1998.
518. Schiavi A, Hudder A, and Werner R. Connexin43 mRNA contains a functional internal ribosome entry site. FEBS Lett 464:
118 –122, 1999.
519. Schiller PC, Mehta PP, Roos BA, and Howard GA. Hormonal
regulation of intercellular communication: parathyroid hormone
increases connexin 43 gene expression and gap-junctional communication in osteoblastic cells. Mol Endocrinol 6: 1433–1440, 1992.
520. Schubert AL, Schubert W, Spray DC, and Lisanti MP. Connexin family members target to lipid raft domains and interact with
caveolin-1. Biochemistry 41: 5754 –5764, 2002.
521. Schwarz HJ, Chang YS, Hennemann H, Dahl E, Lalley PA, and
Willecke K. Chromosomal assignments of mouse connexin genes,
coding for gap junctional proteins, by somatic cell hybridization.
Somat Cell Mol Genet 18: 351–359, 1992.
522. Scott DA, Kraft ML, Stone EM, Sheffield VC, and Smith RJ.
Connexin mutations and hearing loss. Nature 391: 32, 1998.
523. Segal SS and Duling BR. Conduction of vasomotor responses in
arterioles: a role for cell-to-cell coupling? Am J Physiol Heart Circ
Physiol 256: H838 –H845, 1989.
524. Seki K and Komuro T. Further observations on the gap-junctionrich cells in the deep muscular plexus of the rat small intestine.
Anat Embryol 197: 135–141, 1998.
525. Seki K and Komuro T. Immunocytochemical demonstration of
the gap junction proteins connexin 43 and connexin 45 in the
musculature of the rat small intestine. Cell Tissue Res 306: 417–
422, 2001.
526. Serre-Beinier V, Le Gurun S, Belluardo N, Trovato-Salinaro
A, Charollais A, Haefliger JA, Condorelli DF, and Meda P.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
491.
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
CONNEXIN CHANNELS
Physiol Rev • VOL
550. Spray DC. Physiological and pharmacological regulation of gap
junction channels. In: Molecular Mechanisms of Epithelial Cell
Junctions: From Development to Disease, edited by Citi S. Austin,
TX: Landes, 1994, p. 195–215.
551. Spray DC. Molecular physiology of gap junction channels. Clin
Exp Pharmacol Physiol 23: 1038 –1040, 1996.
552. Spray DC and Dermietzel R. Gap Junctions in the Nervous
System. New York: Chapman and Hall, 1996.
553. Spray DC, Moreno AP, Kessler JA, and Dermietzel R. Characterization of gap junctions between cultured leptomeningeal cells.
Brain Res 568: 1–14, 1991.
554. Starich T, Lee RY, Panzarella C, Avery L, and Shaw JE. eat-5
and unc-7 represent a multigene family in Caenorhabditis elegans
involved in cell-cell coupling. J Cell Biol 134: 537–548, 1996.
555. Starich T, Sheehan M, Jadrich J, and Shaw J. Innexins in C.
elegans. Cell Commun Adhes 8: 311–314, 2001.
556. Stauffer KA. The gap junction proteins beta 1-connexin (connexin-32) and beta 2-connexin (connexin-26) can form heteromeric
hemichannels. J Biol Chem 270: 6768 – 6772, 1995.
557. Stauffer KA, Kumar NM, Gilula NB, and Unwin N. Isolation and
purification of gap junction channels. J Cell Biol 115: 141–150, 1991.
558. Stauffer PL, Zhao H, Luby-Phelps K, Moss RL, Star RA, and
Muallem S. Gap junction communication modulates [Ca2⫹]i oscillations and enzyme secretion in pancreatic acini. J Biol Chem 268:
19769 –19775, 1993.
559. Steele EC Jr, Lyon MF, Favor J, Guillot PV, Boyd Y, and
Church RL. A mutation in the connexin 50 (Cx50) gene is a
candidate for the No2 mouse cataract. Curr Eye Res 17: 883– 889,
1998.
560. Steger K, Tetens F, and Bergmann M. Expression of connexin
43 in human testis. Histochem Cell Biol 112: 215–220, 1999.
561. Stock A and Sies H. Thyroid hormone receptors bind to an
element in the connexin43 promoter. Biol Chem 381: 973–979,
2000.
562. Stout CE, Costantin JL, Naus CC, and Charles AC. Intercellular calcium signaling in astrocytes via ATP release through connexin hemichannels. J Biol Chem 277: 10482–10488, 2002.
563. Stumpel F, Ott T, Willecke K, and Jungermann K. Connexin 32
gap junctions enhance stimulation of glucose output by glucagon
and noradrenaline in mouse liver. Hepatology 28: 1616 –1620, 1998.
564. Suárez S and Ballmer-Hofer K. VEGF transiently disrupts gap
junctional communication in endothelial cells. J Cell Sci 114: 1229 –
1235, 2001.
565. Sullivan R, Ruangvoravat C, Joo D, Morgan J, Wang BL, Wang
XK, and Lo CW. Structure, sequence and expression of the mouse
Cx43 gene encoding connexin 43. Gene 130: 191–199, 1993.
566. Swenson KI, Jordan JR, Beyer EC, and Paul DL. Formation of
gap junctions by expression of connexins in Xenopus oocyte pairs.
Cell 57: 145–155, 1989.
567. Swenson KI, Piwnica-Worms H, McNamee H, and Paul DL.
Tyrosine phosphorylation of the gap junction protein connexin43 is
required for the pp60v-src-induced inhibition of communication.
Cell Regul 1: 989 –1002, 1990.
568. Takahashi N, Joh T, Yokohama Y, Seno K, Nomura T, Ohara
H, Ueda F, and Itoh M. Importance of gap junction in gastric
mucosal restitution from acid-induced injury. J Lab Clin Med 136:
93–99, 2000.
569. Takeda A, Hashimoto E, Yamamura H, and Shimazu T. Phosphorylation of liver gap junction protein by protein kinase C. FEBS
Lett 210: 169 –172, 1987.
570. Takeda A, Saheki S, Shimazu T, and Takeuchi N. Phosphorylation of the 27-kDa gap junction protein by protein kinase C in
vitro and in rat hepatocytes. J Biochem 106: 723–727, 1989.
571. Tan IP, Roy C, Sáez JC, Sáez CG, Paul DL, and Risley MS.
Regulated assembly of connexin33 and connexin43 into rat Sertoli
cell gap junctions. Biol Reprod 54: 1300 –1310, 1996.
572. Taylor AB, Kreulen D, and Prosser CL. Electron microscopy of
the connective tissues between longitudinal and circular muscle of
small intestine of cat. Am J Anat 150: 427– 441, 1977.
573. Temme A, Buchmann A, Gabriel HD, Nelles E, Schwarz M, and
Willecke K. High incidence of spontaneous and chemically induced liver tumors in mice deficient for connexin32. Curr Biol 7:
713–716, 1997.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
Cx36 preferentially connects beta-cells within pancreatic islets.
Diabetes 49: 727–734, 2000.
527. Serrière V, Berthon B, Boucherie S, Jacquemin E, Guillon G,
Claret M, and Tordjmann T. Vasopressin receptor distribution in
the liver controls calcium wave propagation and bile flow. FASEB
J 15: 1484 –1486, 2001.
528. Seul KH and Beyer EC. Heterogeneous localization of connexin40 in the renal vasculature. Microvasc Res 59: 140 –148, 2000.
529. Seul KH and Beyer EC. Mouse connexin37: gene structure and
promoter analysis. Biochim Biophys Acta 1492: 499 –504, 2000.
530. Seul KH, Tadros PN, and Beyer EC. Mouse connexin40: gene
structure and promoter analysis. Genomics 46: 120 –126, 1997.
531. Severs NJ. The cardiac muscle cell. Bioessays 22: 188 –199, 2000.
532. Severs NJ, Rothery S, Dupont E, Coppen SR, Yeh HI, Ko YS,
Matsushita T, Kaba R, and Halliday D. Immunocytochemical
analysis of connexin expression in the healthy and diseased cardiovascular system. Microsc Res Tech 52: 301–322, 2001.
533. Severs NJ, Shovel KS, Slade AM, Powell T, Twist VW, and
Green CR. Fate of gap junctions in isolated adult mammalian
cardiomyocytes. Circ Res 65: 22– 42, 1989.
534. Shibata Y, Kumai M, Nishii K, and Nakamura K. Diversity and
molecular anatomy of gap junctions. Med Electron Microsc 34:
153–159, 2001.
535. Shibata Y, Manjunath CK, and Page E. Differences between
cytoplasmic surfaces of deep-etched heart and liver gap junctions.
Am J Physiol Heart Circ Physiol 249: H690 –H693, 1985.
536. Shiels A, Mackay D, Ionides A, Berry V, Moore A, and Bhattacharya S. A missense mutation in the human connexin50 gene
(GJA8) underlies autosomal dominant “zonular pulverulent” cataract, on chromosome 1q. Am J Hum Genet 62: 526 –532, 1998.
537. Shimono M, Muramatsu T, Ihara A, Enokiya Y, Hashimoto S,
and Inoue T. Connexins in the developing salivary glands. Eur J
Morphol 36 Suppl.: 112–117, 1998.
538. Shimono M, Young Lee C, Matsuzaki H, Ishikawa H, Inoue T,
Hashimoto S, and Muramatsu T. Connexins in salivary glands.
Eur J Morphol 38: 257–261, 2000.
539. Simon AM. Gap junctions: more roles and new structural data.
Trends Cell Biol 9: 169 –170, 1999.
540. Simon AM and Goodenough DA. Diverse functions of vertebrate
gap junctions. Trends Cell Biol 8: 477– 483, 1998.
541. Simon AM, Goodenough DA, Li E, and Paul DL. Female infertility in mice lacking connexin 37. Nature 385: 525–529, 1997.
542. Simon AM, Goodenough DA, and Paul DL. Mice lacking connexin40 have cardiac conduction abnormalities characteristic of
atrioventricular block and bundle branch block. Curr Biol 8: 295–
298, 1998.
543. Skerrett IM, Aronowitz J, Shin JH, Cymes G, Kasperek E,
Cao FL, and Nicholson BJ. Identification of amino acid residues
lining the pore of a gap junction channel. J Cell Biol 159: 349 –360,
2002.
544. Söhl G, Degen J, Teubner B, and Willecke K. The murine gap
junction gene connexin36 is highly expressed in mouse retina and
regulated during brain development. FEBS Lett 428: 27–31, 1998.
544a.Söhl G, Eiberger J, Jung YT, Kozak CA, and Willecke K. The
mouse gap junction gene connexin 29 is highly expressed in sciatic
nerve and regulated during brain development. Biol Chem 382:
973–978, 2001.
545. Söhl G, Gillen C, Bosse F, Gleichmann M, Muller HW, and
Willecke K. A second alternative transcript of the gap junction
gene connexin32 is expressed in murine Schwann cells and modulated in injured sciatic nerve. Eur J Cell Biol 69: 267–275, 1996.
546. Söhl G, Guldenagel M, Traub O, and Willecke K. Connexin
expression in the retina. Brain Res Rev 32: 138 –145, 2000.
547. Söhl G, Theis M, Hallas G, Brambach S, Dahl E, Kidder G, and
Willecke K. A new alternatively spliced transcript of the mouse
connexin32 gene is expressed in embryonic stem cells, oocytes,
and liver. Exp Cell Res 266: 177–186, 2001.
548. Sosinsky GE. Molecular organization of gap junction membrane
channels. J Bioenerg Biomembr 28: 297–309, 1996.
549. Sotkis A, Wang XG, Yasumura T, Peracchia LL, Persechini A,
Rash JE, and Peracchia C. Calmodulin colocalizes with connexins and plays a direct role in gap junction channel gating. Cell
Commun Adhes 8: 277–281, 2001.
1397
1398
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER
Physiol Rev • VOL
593. Unger VM, Kumar NM, Gilula NB, and Yeager M. Three-dimensional structure of a recombinant gap junction membrane channel.
Science 283: 1176 –1180, 1999.
594. Uwin PN and Ennis PD. Calcium-mediated changes in gap junction structure: evidence from the low angle X-ray pattern. J Cell
Biol 97: 1459 –1466, 1983.
595. Uwin PN and Zampighi G. Structure of the junction between
communicating cells. Nature 283: 545–549, 1980.
596. Valdimarsson G, De Sousa PA, and Kidder GM. Coexpression
of gap junction proteins in the cumulus-oocyte complex. Mol Reprod Dev 36: 7–15, 1993.
597. Valiunas V. Biophysical properties of connexin-45 gap junction
hemichannels studied in vertebrate cells. J Gen Physiol 119: 147–
164, 2002.
598. Valiunas V, Niessen H, Willecke K, and Weingart R. Electrophysiological properties of gap junction channels in hepatocytes
isolated from connexin32-deficient and wild-type mice. Pflügers
Arch 437: 846 – 856, 1999.
599. Valiunas V and Weingart R. Electrical properties of gap junction
hemichannels identified in transfected HeLa cells. Pflügers Arch
440: 366 –379, 2000.
600. Van der Heyden MA, Rook MB, Hermans MM, Rijksen G,
Boonstra J, Defize LH, and Destree OH. Identification of connexin43 as a functional target for Wnt signalling. J Cell Sci 111:
1741–1749, 1998.
601. Vanderhyden BC, Caron PJ, Buccione R, and Eppig JJ. Developmental pattern of the secretion of cumulus-expansion enabling
factor by mouse oocytes and the role of oocytes in promoting
granulosa cell differentiation. Dev Biol 140: 307–317, 1990.
602. Vanderhyden BC, Cohen JN, and Morley P. Mouse oocytes
regulate granulosa cell steroidogenesis. Endocrinology 133: 423–
426, 1993.
603. Van der Velden HMW and Jongsma HJ. Cardiac gap junctions
and connexins: their role in atrial fibrillation and potential as
therapeutic targets. Cardiovasc Res 54: 270 –279, 2002.
604. Van Eldik LJ, Hertzberg EL, Berdan RC, and Gilula NB. Interaction of calmodulin and other calcium-modulated proteins with
mammalian and arthropod junctional membrane proteins. Biochem
Biophys Res Commun 126: 825– 832, 1985.
605. Van Kempen MJ, Fromaget C, Gros D, Moorman AF, and
Lamers WH. Spatial distribution of connexin43, the major cardiac
gap junction protein, in the developing and adult rat heart. Circ Res
68: 1638 –1651, 1991.
606. Van Kempen MJ and Jongsma HJ. Distribution of connexin37,
connexin40 and connexin43 in the aorta and coronary artery of
several mammals. Histochem Cell Biol 112: 479 – 486, 1999.
607. Vanoye CG, Vergara LA, and Reuss L. Isolated epithelial cells
from amphibian urinary bladder express functional gap junctional
hemichannels. Am J Physiol Cell Physiol 276: C279 –C284, 1999.
608. Van Rijen H, van Kempen MJ, Analbers LJ, Rook MB, van
Ginneken AC, Gros D, and Jongsma HJ. Gap junctions in human umbilical cord endothelial cells contain multiple connexins.
Am J Physiol Cell Physiol 272: C117–C130, 1997.
609. Van Rijen HV, van Kempen MJ, Postma S, and Jongsma HJ.
Tumour necrosis factor alpha alters the expression of connexin43,
connexin40, and connexin37 in human umbilical vein endothelial
cells. Cytokine 10: 258 –264, 1998.
610. Van Rijen HV, van Veen TA, Hermans MM, and Jongsma HJ.
Human connexin40 gap junction channels are modulated by cAMP.
Cardiovasc Res 45: 941–951, 2000.
611. Van Rijen HV, van Veen TA, van Kempen MJ, Wilms-Schopman FJ, Potse M, Krueger O, Willecke K, Opthof T, Jongsma
HJ, and de Bakker JM. Impaired conduction in the bundle
branches of mouse hearts lacking the gap junction protein connexin40. Circulation 103: 1591–1598, 2001.
612. VanSlyke JK and Musil LS. Dislocation and degradation from the
ER are regulated by cytosolic stress. J Cell Biol 157: 381–394, 2002.
613. Van Veen TA, van Rijen HV, and Jongsma HJ. Electrical conductance of mouse connexin45 gap junction channels is modulated
by phosphorylation. Cardiovasc Res 46: 496 –510, 2000.
614. Van Veen TA, van Rijen HVM, and Opthof T. Cardiac gap
junction channels: modulation of expression and channel properties. Cardiovasc Res 51: 217–229, 2001.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
574. Temme A, Stumpel F, Sohl G, Rieber EP, Jungermann K,
Willecke K, and Ott T. Dilated bile canaliculi and attenuated
decrease of nerve-dependent bile secretion in connexin32-deficient
mouse liver. Pflügers Arch 442: 961–966, 2001.
575. TenBroek EM, Lampe PD, Solan JL, Reynhout JK, and Johnson RG. Ser364 of connexin43 and the upregulation of gap junction
assembly by cAMP. J Cell Biol 155: 1307–1318, 2001.
576. Thomas SA, Schuessler RB, Berul CI, Beardslee MA, Beyer
EC, Mendelsohn ME, and Saffitz JE. Disparate effects of deficient expression of connexin43 on atrial and ventricular conduction: evidence for chamber-specific molecular determinants of conduction. Circulation 97: 686 – 691, 1998.
577. Tibbitts TT, Caspar DLD, Phillips WC, and Goodenough DA.
Diffraction diagnosis of protein folding in gap junction connexons.
Biophys J 57: 1025–1036, 1990.
578. Tordjmann T, Berthon B, Claret M, and Combettes L. Coordinated intercellular calcium waves induced by noradrenaline in
rat hepatocytes: dual control by gap junction permeability and
agonist. EMBO J 16: 5398 –5407, 1997.
579. Toyofuku T, Akamatsu Y, Zhang H, Kuzuya T, Tada M, and
Hori M. c-Src regulates the interaction between connexin-43 and
ZO-1 in cardiac myocytes. J Biol Chem 276: 1780 –1788, 2001.
580. Toyofuku T, Yabuki M, Otsu K, Kuzuya T, Hori M, and Tada
M. Intercellular calcium signaling via gap junction in connexin-43transfected cells. J Biol Chem 273: 1519 –1528, 1998.
581. Toyofuku T, Yabuki M, Otsu K, Kuzuya T, Hori M, and Tada
M. Direct association of the gap junction protein connexin-43 with
ZO-1 in cardiac myocytes. J Biol Chem 273: 12725–12731, 1998.
582. Tran D, Stelly N, Tordjmann T, Durroux T, Dufour MN, Forchioni A, Seyer R, Claret M, and Guillon G. Distribution of
signaling molecules involved in vasopressin-induced Ca2⫹ mobilization in rat hepatocyte multiplets. J Histochem Cytochem 47:
601– 616, 1999.
583. Traub O, Butterweck A, Elfgag C, Hertlein B, Balzer K, Gregs
U, Hafemann B, and Willecke K. Immunochemical characterization of connexin31, -37, -40, -43, and -45 in cultured primary cells,
transfected cell lines and and murine tissues. In: Progress in Cell
Research, Intercellular Communication Through Gap Junctions,
edited by Kano K, Shiba Y, Shibata Y, and Shimazu T. Amsterdam:
Elsevier Science, 1995, vol. 4, p. 343–347.
584. Traub O, Hertlein B, Kasper M, Eckert R, Krisciukaitis A,
Hülser D, and Willecke K. Characterization of the gap junction
protein connexin37 in murine endothelium, respiratory epithelium,
and after transfection in human HeLa cells. Eur J Cell Biol 77:
313–322, 1998.
585. Traub O, Look J, Dermietzel R, Brummer F, Hülser D, and
Willecke K. Comparative characterization of the 21-kD and 26-kD
gap junction proteins in murine liver and cultured hepatocytes.
J Cell Biol 108: 1039 –1051, 1989.
586. Traub O, Look J, Paul D, and Willecke K. Cyclic adenosine
monophosphate stimulates biosynthesis and phosphorylation of
the 26 kDa gap junction protein in cultured mouse hepatocytes.
Eur J Cell Biol 43: 48 –54, 1987.
587. Trexler EB, Bennett MV, Bargiello TA, and Verselis VK. Voltage gating and permeation in a gap junction hemichannel. Proc Natl
Acad Sci USA 93: 5836 –5841, 1996.
588. Trexler EB, Bukauskas FF, Bennett MV, Bargiello TA, and
Verselis VK. Rapid and direct effects of pH on connexins revealed
by the connexin46 hemichannel preparation. J Gen Physiol 113:
721–742, 1999.
589. Trexler EB, Bukauskas FF, Kronengold J, Bargiello TA, and
Verselis VK. The first extracellular loop domain is a major determinant of charge selectivity in connexin46 channels. Biophys J 79:
3036 –3051, 2000.
590. Tu ZJ, Pan W, Gong Z, and Kiang DT. Involving AP-2 transcription factor in connexin 26 up-regulation during pregnancy and
lactation. Mol Reprod Dev 59: 17–24, 2001.
591. Uchida Y, Matsuda K, Sasahara K, Kawabata H, and Nishioka
M. Immunohistochemistry of gap junctions in normal and diseased
gastric mucosa of humans. Gastroenterology 109: 1492–1496, 1995.
592. Unger VM, Kumar NM, Gilula NB, and Yeager M. Projection
structure of a gap junction membrane channel at 7 Å resolution.
Nat Struct Biol 4: 39 – 43, 1997.
CONNEXIN CHANNELS
Physiol Rev • VOL
637.
638.
639.
640.
641.
642.
643.
644.
645.
646.
647.
648.
649.
650.
651.
652.
653.
654.
655.
656.
657.
lating hormone induces a gap junction-dependent dynamic change
in [cAMP] and protein kinase A in mammalian oocytes. Dev Biol
246: 441– 454, 2002.
Weidmann S. The electrical constants of Purkinje fibers. J Physiol
118: 348 –360, 1952.
Werner R. IRES elements in connexin genes: a hypothesis explaining the need for connexins to be regulated at the translational level.
IUBMB Life 50: 173–176, 2000.
Werner R, Levine E, Rabadan-Diehl C, and Dahl G. Formation
of hybrid cell-cell channels. Proc Natl Acad Sci USA 86: 5380 –5384,
1989.
Werner R, Levine E, Rabadan-Diehl C, and Dahl G. Gating
properties of connexin32 cell-cell channels and their mutants expressed in Xenopus oocytes. Proc R Soc Lond B Biol Sci 243: 5–11,
1991.
White TW. Functional analysis of human Cx26 mutations associated with deafness. Brain Res Rev 32: 181–183, 2000.
White TW, Bruzzone R, Goodenough DA, and Paul DL. Mouse
Cx50, a functional member of the connexin family of gap junction
proteins, is the lens fiber protein MP70. Mol Biol Cell 3: 711–720,
1992.
White TW, Bruzzone R, Wolfram S, Paul DL, and Goodenough
DA. Selective interactions among the multiple connexin proteins
expressed in the vertebrate lens: the second extracellular domain is
a determinant of compatibility between connexins. J Cell Biol 125:
879 – 892, 1994.
White TW, Deans MR, O’Brien J, Al-Ubaidi MR, Goodenough
DA, Ripps H, and Bruzzone R. Functional characteristics of skate
connexin35, a member of the gamma subfamily of connexins expressed in the vertebrate retina. Eur J Neurosci 11: 1883–1890,
1999.
White TW, Deans MR, Kelsell DP, and Paul DL. Connexin
mutations in deafness. Nature 394: 630 – 631, 1998.
White TW, Goodenough DA, and Paul DL. Targeted ablation of
connexin50 in mice results in microphthalmia and zonular pulverulent cataracts. J Cell Biol 143: 815– 825, 1998.
White TW and Paul DL. Genetic diseases and gene knockouts
reveal diverse connexin functions. Annu Rev Physiol 61: 283–310,
1999.
White TW, Paul DL, Goodenough DA, and Bruzzone R. Functional analysis of selective interactions among rodent connexins.
Mol Biol Cell 6: 459 – 470, 1995.
White TW, Sellito C, Paul DL, and Goodenough DA. Prenatal
lens development in connexin43 and connexin50 double knockout
mice. Invest Ophthalmol Vis Sci 42: 2916 –2923, 2001.
Wiesen JF and Midgley AR Jr. Changes in expression of connexin 43 gap junction messenger ribonucleic acid and protein
during ovarian follicular growth. Endocrinology 133: 741–746,
1993.
Wiesen JF and Midgley AR Jr. Expression of connexin 43 gap
junction messenger ribonucleic acid and protein during follicular
atresia. Biol Reprod 50: 336 –348, 1994.
Wilgenbus KK, Kirkpatrick CJ, Knuechel R, Willecke K, and
Traub O. Expression of Cx26, Cx32 and Cx43 gap junction proteins in normal and neoplastic human tissues. Int J Cancer 51:
522–529, 1992.
Willecke K, Eiberger J, Degen J, Eckardt D, Romualdi A,
Guldenagel M, Deutsch U, and Sohl G. Structural and functional
diversity of connexin genes in the mouse and human genome. Biol
Chem 383: 725–737, 2002.
Willecke K, Jungbluth S, Dahl E, Hennemann H, Heynkes R,
and Grzeschik K-H. Six genes of the human connexin gene family
coding for gap junctional proteins are assigned to four different
human chromosomes. Eur J Cell Biol 53: 275–280, 1990.
Winterhager E, Brummer F, Dermietzel R, Hülser DF, and
Denker HW. Gap junction formation in rabbit uterine epithelium
in response to embryo recognition. Dev Biol 126: 203–211, 1988.
Winterhager E, Grummer R, Jahn E, Willecke K, and Traub O.
Spatial and temporal expression of connexin26 and connexin43 in
rat endometrium during trophoblast invasion. Dev Biol 157: 399 –
409, 1993.
Xia JH, Liu CY, Tang BS, Pan Q, Huang L, Dai HP, Zhang BR,
Xie W, Hu DX, Zheng D, Shi XL, Wang DA, Xia K, Yu KP, Liao
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
615. Varanda WA and Campos de Carvalho AC. Intercellular communication between mouse Leydig cells. Am J Physiol Cell Physiol
267: C563–C569, 1994.
616. Vaughan DK and Lasater EM. Acid phosphatase localization in
endocytosed horizontal cell gap junctions. Vis Neurosci 8: 77– 81,
1992.
617. Veenstra RD, Wang HZ, Beblo DA, Chilton MG, Harris AL,
Beyer EC, and Brink PR. Selectivity of connexin-specific gap
junctions does not correlate with channel conductance. Circ Res
77: 1156 –1165, 1995.
618. Veenstra RD, Wang HZ, Beyer EC, and Brink PR. Selective dye
and ionic permeability of gap junction channels formed by connexin45. Circ Res 75: 483– 490, 1994.
619. Veenstra RD, Wang HZ, Beyer EC, Ramanan SV, and Brink PR.
Connexin37 forms high conductance gap junction channels with
subconductance state activity and selective dye and ionic permeabilities. Biophys J 66: 1915–1928, 1994.
620. Veenstra RD, Wang HZ, Westphale EM, and Beyer EC. Multiple
connexins confer distinct regulatory conductance properties of gap
junctions in developing heart. Circ Res 71: 1277–1283, 1992.
621. Verderio C, Bruzzone S, Zocchi E, Fedele E, Schenk U, De
Flora A, and Matteoli M. Evidence of a role for cyclic ADP-ribose
in calcium signalling and neurotransmitter release in cultured astrocytes. J Neurochem 78: 646 – 657, 2001.
622. Verheijck EE, van Kempen MJ, Veereschild M, Lurvink J,
Jongsma HJ, and Bouman LN. Electrophysiological features of
the mouse sinoatrial node in relation to connexin distribution.
Cardiovasc Res 52: 40 –50, 2001.
623. Verheule S, van Kempen MJ, Postma S, Rook MB, and
Jongsma HJ. Gap junctions in the rabbit sinoatrial node. Am J
Physiol Heart Circ Physiol 280: H2103–H2115, 2001.
624. Vliagoftis H, Hutson AM, Mahmudi-Azer S, Kim H, Rumsaeng
V, Oh CK, Moqbel R, and Metcalfe DD. Mast cells express
connexins on their cytoplasmic membrane. J Allergy Clin Immunol 103: 656 – 662, 1999.
625. Vozzi C, Dupont E, Coppen SR, Yeh HI, and Severs NJ. Chamber-related differences in connexin expression in the human heart.
J Mol Cell Cardiol 31: 991–1003, 1999.
626. Vozzi C, Formenton A, Chanson A, Senn A, Sahli R, Shaw P,
Nicod P, Germond M, and Haefliger JA. Involvement of connexin 43 in meiotic maturation of bovine oocytes. Reproduction
122: 619 – 628, 2001.
627. Vozzi C, Ullrich S, Charollais A, Philippe J, Orci L, and Meda
P. Adequate connexin-mediated coupling is required for proper
insulin production. J Cell Biol 131: 1561–1572, 1995.
628. Walcott B, Moore LC, Birzgalis A, Claros N, Valiunas V, Ott T,
Willecke K, and Brink PR. Role of gap junctions in fluid secretion
of lacrimal glands. Am J Physiol Cell Physiol 282: C501–C507, 2002.
629. Wang Y and Daniel EE. Gap junctions in gastrointestinal muscle
contain multiple connexins. Am J Physiol Gastrointest Liver
Physiol 281: G533–G543, 2001.
630. Wang Y, Mehta PP, and Rose B. Inhibition of glycosylation
induces formation of open connexin-43 cell-to-cell channels and
phosphorylation and triton X-100 insolubility of connexin-43. J Biol
Chem 270: 26581–26585, 1995.
631. Wang Y and Rose B. Clustering of Cx43 cell-to-cell channels into
gap junction plaques: regulation by cAMP and microfilaments.
J Cell Sci 108: 3501–3508, 1995.
632. Wang Y and Rose B. An inhibition of gap-junctional communication by cadherins. J Cell Sci 110: 301–309, 1997.
633. Warn-Cramer BJ, Cottrell GT, Burt JM, and Lau AF. Regulation of connexin-43 gap junctional intercellular communication by
mitogen-activated protein kinase. J Biol Chem 273: 9188 –9196,
1998.
634. Warn-Cramer BJ, Lampe PD, Kurata WE, Kanemitsu MY, Loo
LWM, Eckhart W, and Lau AF. Characterization of the mitogenactivated protein kinase phosphorylation sites on the connexin-43
gap junction protein. J Biol Chem 271: 3779 –3786, 1996.
635. Webb RJ, Bains H, Cruttwell C, and Carroll J. Gap-junctional
communication in mouse cumulus-oocyte complexes: implications
for the mechanism of meiotic maturation. Reproduction 123: 41–52,
2002.
636. Webb RJ, Marshall F, Swann K, and Carroll J. Follicle-stimu-
1399
1400
658.
659.
660.
661.
662.
664.
665.
666.
667.
668.
669.
670.
XD, Feng Y, Yang YF, Xiao JY, Xie DH, and Huang JZ. Mutations in the gene encoding gap junction protein beta-3 associated
with autosomal dominant hearing impairment. Nat Genet 20: 370 –
373, 1998.
Xia AP, Ikeda K, Katori Y, Oshima T, Kikuchi T, and Takasaka
T. Expression of connexin 31 in the developing mouse cochlea.
Neuroreport 11: 2449 –2453, 2000.
Xu X and Ebihara L. Characterization of a mouse Cx50 mutation
associated with the No2 mouse cataract. Invest Ophthalmol Vis Sci
40: 1844 –1850, 1999.
Yamanaka I, Kuraoka A, Inai T, Ishibashi T, and Shibata Y.
Differential expression of major gap junction proteins, connexins
26 and 32, in rat mammary glands during pregnancy and lactation.
Histochem Cell Biol 115: 277–284, 2001.
Yamaoka K, Nouchi T, Kohashi T, Marumo F, and Sato C.
Expression of gap junction protein connexin 32 in chronic liver
diseases. Liver 20: 104 –107, 2000.
Yamasaki H, Omori Y, Zaidan-Dagli ML, Mironov N, Mesnil M,
and Krutovskikh V. Genetic and epigenetic changes of intercellular communication genes during multistage carcinogenesis. Cancer Detect Prev 23: 273–279, 1999.
Yancey SB, John SA, Lal R, Austin BJ, and Revel JP. The 43-kD
polypeptide of heart gap junctions: immunolocalization, topology,
and functional domains. J Cell Biol 108: 2241–2254, 1989.
Yao J, Morioka T, and Oite T. PDGF regulates gap junction
communication and connexin43 phosphorylation by PI 3-kinase in
mesangial cells. Kidney Int 57: 1915–1926, 2000.
Yeager M. Structure of cardiac gap junction intercellular channels.
J Struct Biol 121: 231–245, 1998.
Yeager M, Unger VM, and Falk MM. Synthesis, assembly and
structure of gap junction intercellular channels. Curr Opin Struct
Biol 8: 517–524, 1998.
Yeh HI, Lupu F, Dupont E, and Severs NJ. Upregulation of
connexin43 gap junctions between smooth muscle cells after balloon catheter injury in the rat carotid artery. Arterioscler Thromb
Vasc Biol 17: 3174 –3184, 1997.
Yeh HI, Rothery S, Dupont E, Coppen SR, and Severs NJ.
Individual gap junction plaques contain multiple connexins in arterial endothelium. Circ Res 83: 1248 –1263, 1998.
Yin X, Gu S, and Jiang JX. The development-associated cleavage
of lens connexin 45.6 by caspase-3-like protease is regulated by
casein kinase II-mediated phosphorylation. J Biol Chem 276:
34567–34572, 2001.
Yin X, Jedrzejewski PT, and Jiang JX. Casein kinase II phos-
Physiol Rev • VOL
671.
672.
673.
674.
675.
676.
677.
678.
679.
680.
681.
682.
phorylates lens connexin 45.6 and is involved in its degradation.
J Biol Chem 275: 6850 – 6856, 2000.
Yoshimura T, Satake M, Ohnishi A, Tsutsumi Y, and Fujikura
Y. Mutations of connexin32 in Charcot-Marie-Tooth disease type X
interfere with cell-to-cell communication but not cell proliferation
and myelin-specific gene expression. J Neurosci Res 51: 154 –161,
1998.
Yoshizaki G and Patino R. Molecular cloning, tissue distribution,
and hormonal control in the ovary of Cx41 mRNA, a novel Xenopus
connexin gene transcript. Mol Reprod Dev 42: 7–18, 1995.
You S, Li W, and Lin T. Expression and regulation of connexin43
in rat Leydig cells. J Endocrinol 166: 447– 453, 2000.
Yu W, Dahl G, and Werner R. The connexin43 gene is responsive
to oestrogen. Proc R Soc Lond B Biol Sci 255: 125–132, 1994.
Zamir O and Hanani M. Intercellular dye-coupling in intestinal
smooth muscle. Are gap junctions required for intercellular coupling? Experientia 46: 1002–1005, 1990.
Zampighi GA, Loo DD, Kreman M, Eskandari S, and Wright
EM. Functional and morphological correlates of connexin50 expressed in Xenopus laevis oocytes. J Gen Physiol 113: 507–524,
1999.
Zelante L, Gasparini P, Estivill X, Melchionda S, D’Agruma L,
Govea N, Mila M, Monica MD, Lutfi J, Shohat M, Mansfield E,
Delgrosso K, Rappaport E, Surrey S, and Fortina P. Connexin26 mutations associated with the most common form of
non-syndromic neurosensory autosomal recessive deafness
(DFNB1) in Mediterraneans. Hum Mol Genet 6:1605–1609, 1997.
Zhang DQ and McMahon DG. Gating of retinal horizontal cell
hemi gap junction channels by voltage, Ca2⫹, and retinoic acid. Mol
Vis 7: 247–252, 2001.
Zhang JT and Nicholson BJ. The topological structure of connexin 26 and its distribution compared to connexin 32 in hepatic
gap junctions. J Membr Biol 139: 15–29, 1994.
Zhang M and Thorgeirsson SS. Modulation of connexins during
differentiation of oval cells into hepatocytes. Exp Cell Res 213:
37– 42, 1994.
Zhou XW, Pfahnl A, Werner R, Hudder A, Llanes A, Luebke A,
and Dahl G. Identification of a pore lining segment in gap junction
hemichannels. Biophys J 72: 1946 –1953, 1997.
Zimmer DB, Green CR, Evans WH, and Gilula NB. Topological
analysis of the major protein in isolated intact rat liver gap junctions and gap junction-derived single membrane structures. J Biol
Chem 262: 7751–7763, 1987.
83 • OCTOBER 2003 •
www.prv.org
Downloaded from http://physrev.physiology.org/ by 10.220.33.2 on July 4, 2017
663.
SÁEZ, BERTHOUD, BRAÑES, MARTÍNEZ, AND BEYER

Download Report

Print

Paperzz.com

Your Paperzz