1277
Rapid Communication
Multiple Connexins Confer Distinct Regulatory
and Conductance Properties of Gap Junctions
in Developing Heart
R.D. Veenstra, H.-Z. Wang, E.M. Westphale, and E.C. Beyer
Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017
Multiple gap junction proteins (connexins) and channels have been identified in developing and adult
heart. Functional expression of the three connexins found in chick heart (connexin42, connexin43, and
connexin45) by stable transfection of communication-deficient neuro2A (N2A) cells revealed that all three
connexin cDNAs are capable of forming physiologically distinct gap junctions that differ in their
transjunctional voltage dependence and unitary channel conductances. The transjunctional voltage
dependences of connexin45 and connexin42 closely resembled those of 4-day and 18-day embryonic chick
heart gap junctions, respectively. The multiple channel conductances between 80 and 240 pS, including
the predominant 160 pS channel, observed in embryonic chick heart were also common to connexin42.
The expression of multiple gap junction channels with distinct conductance and regulatory properties
within a given tissue may account for developmental changes in intercellular communication. (Circulation
Research 1992;71:1277-1283)
KEY WoRDs * gap junctions * connexins * cardiac development * chicks * channels
T he intercellular channels of cardiac gap junctions
organize the working myocardium and specialized conducting tissues into a functional syncytium, permitting the rapid and synchronous conduction
of action potentials.12 Cardiac myocytes obtained from
different organisms and from chick embryos of different
ages contain gap junctional channels with different
unitary conductances and with differing sensitivity to
transjunctional voltage (Vj).3-7 Gap junctions are
formed by members of a family of related proteins
called connexins, which contain conserved extracellular
and transmembrane domains but divergent cytoplasmic
regions.8 These divergent sequences have been postulated to confer specific channel conductance and regulatory (gating) properties.
The molecular cloning9 and functional expression'0 -4
of connexin43 (Cx43), which is abundant throughout
the cardiovascular system,15 has provided molecular
information about intercellular communication in the
heart. Recently, two additional cardiac connexins, chick
connexin42 (Cx42) and connexin45 (Cx45), have been
identified and cloned.16"7 The presence of these conFrom the Department of Pharmacology (R.D.V., H.-Z.W.),
State University of New York Health Science Center at Syracuse,
and the Departments of Pediatrics, Medicine, and Cell Biology
(E.M.W., E.C.B.), Washington University School of Medicine, St.
Louis, Mo.
Supported by National Institutes of Health grants EY-08368
(E.C.B.), HL-45466 (E.C.B., R.D.V.), and HL-42220 (R.D.V.), an
American Heart Association Clinician Scientist Award, and the
McDonnell Foundation (E.C.B.). E.C.B. and R.D.V. are Established Investigators of the American Heart Association.
Address for correspondence: R.D. Veenstra, PhD, Department
of Pharmacology, SUNY Health Science Center at Syracuse, 750
E. Adams Street, Syracuse, NY 63110.
Received March 5, 1992; accepted July 15, 1992.
nexins and their mammalian homologues in heart cells
has been demonstrated by Northern blotting and immunocytochemistry. Since these different channel proteins
may contribute multiple pathways for the regulation of
cardiac electrical communication, we have sought to
express functionally all three cardiac connexins and
compare the properties of the channels they form with
previous physiological observations of myocardial gap
junctions. We stably transfected communication-deficient mouse neuro2A (N2A) cells with cDNAs encoding
each of the chick connexins.16"8 Use of this system
allows for the resolution of both macroscopic and single
gap junction channel currents, which was not possible in
previous expression studies using Xenopus oocytes.19
Our transfection of N2A cells substitutes a new cell line
for the SKHepl cells used in previous connexin transfection experiments.20 In our hands, this substitution
has two advantages. SKHepl cells contain a low level of
endogenous coupling due to a 25-35-pS channel20'21
and express connexin40.22 In contrast, we failed to
detect electrical coupling in N2A cell pairs or expression of mRNA for any of nine known connexins. The
establishment of double whole-cell recordings was also
improved by the use of N2A cells.
Materials and Methods
RNA Isolation and Northern Blots
Total cellular RNA was prepared from cells, separated on formaldehyde/agarose gels, and transferred to
nylon membranes as previously described.16 Hybridization was performed with specific `2P-labeled DNA
probes prepared using random hexanucleotide primers
and the Klenow fragment of DNA polymerase I.
1278
Circulation Research Vol 71, No 5 November 1992
Cell Cultures
Mouse N2A neuroblastoma cells (ATCC CCL131)
were obtained from the American Type Culture Collection, Rockville, Md. N2A cells were grown in minimal
essential medium (GIBCO/BRL, Gaithersburg, Md.)
supplemented with 10% heat-inactivated (56°C for 30
minutes) fetal calf serum (JRH Biosciences, Lenexa,
Kan.), 1 x nonessential amino acids, 2 mM L-glutamine,
100 units/ml penicillin, and 100 gg/ml streptomycin
(GIBCO/BRL).
Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017
Connexin cDNA Transfection
The cDNAs for chick Cx43,'6 Cx42,18 and Cx4518
were cloned into the EcoRI site of the eukaryotic
expression vector pSFFV-neo.23 N2A cells in 60-mm
dishes were transfected with 20 gg linearized plasmid
using the lipofectin reagent (GIBCO/BRL) according to
the manufacturer's directions, and stable neomycinresistant colonies were selected in 0.5 mg/ml G418
(geneticin, GIBCO/BRL). Connexin expression was
verified by Northern blotting of total RNA prepared
from selected clones.
Electrophysiological Studies
The double whole-cell recording procedures used in
this study were identical to those described previously.5
Patch electrodes had resistances of 2-5 Mfl when filled
with a solution containing (mM) potassium glutamate
110, NaCI 15, KH2PO4 1, MgCl1 4.6, EGTA 5, Na2ATP
3, Na2 phosphocreatine 3, and HEPES 25, pH 7.1. The
cells were bathed in a solution containing (mM) NaCl
142, KCl 1.3, MgSO4 0.8, NaH2PO4 0.9, CaCl2 1.8,
dextrose 5.5, and HEPES 10, pH 7.2. All experiments
were performed at room temperature (20-22°C). Vjs
were elicited by stepping the holding potential of cell 1
(V,) from a common value (V=V2 =-40 mV, where V2
is the holding potential of cell 2) to a new value in
10-mV increments between -140 and +60 mV. Twosecond pulses were applied once every 7 seconds except
when channel activity was observed; then pulse durations were increased to 20 seconds. Junctional current
(I) was taken as the change in holding current of the
nonpulsed cell (12), since the cell 1 current (II) tracing
contains a nonjunctional membrane current associated
with the change in V, in addition to the negative of the
12 signal.
Results
To verify that the different chick cardiac connexins
were capable of forming functional cell-to-cell channels,
we stably transfected the communication-deficient cell
line N2A with the cDNAs for chick Cx42, Cx43, and
Cx45. The parent N2A cell line showed no detectable
gap junctional channels when screened by double
whole-cell patch-clamp recordings (n=23 pairs) and
showed no detectable connexin expression as assayed by
Northern blotting with probes for connexin26, con-
nexin31, connexin32, connexin37, connexin40. Cx42,
Cx43, Cx45, and connexin56 (data not shown). Connexin-transfected N2A clones were selected in G418.
Chromosomal integration of multiple copies of the
connexin cDNAs was confirmed by genomic blotting
(not shown), and connexin expression was confirmed by
Northern blots of total RNA prepared from the selected
Ln 4_
Cl) CV)
C v CV CV
L
z
R.
(0 'I;
CvvC
c
*~~~h
Cx42
m
Cx43
A..*
oC
00
C
x
x
t
S.
Cx45
FIGURE 1. Northern blots demonstrating the expression of
chick connexin42 (Cx42), connexin43 (Cx43), and connexin45 (Cx45) in transfected cells. Total cellular RNA was
prepared from NMA cells or tissues, separated on formaldehyde/agarose gels (10 pg per lane), and transferred to nylon
membranes; hybridization was performed using connexinspecific 3"P-labeled DNA probes. The probe used is indicated
in each paneL Each probe was hybridized to RNA prepared
from N2M cells transfected with the pSFFV-neo vector alone
(indicated as N2A), to RNA from two different clones
transfected with pSFFV-neo-connexin cDNA constructs
(N2M-Cx42, -Cx43, or -Cx45), and to a positive control RNA
from a 10-day embryonic chick tissue rich in that connexin
(heart for Cx42 and Cx45, lens for Cx43). Cx43 mRNA is
approximately 10-fold more abundant in 10-day chick embryo
lens than heart.'6 In each case, there is no detectable hybridization to RNA from cells transfected with vector alone,
whereas the connexin-transfected cell RNAs contain a band of
the mobility expected for the N2A-connexin constructs. The
differences in connexin mRNA sizes are due to differences in
cDNA insert sizes in the constructs. Apparent minor bands
may reflect RNA degradation or aberrant splicing of expressed
sequences.
clones (Figure 1). In all cases, RNA prepared from the
connexin-transfected cells contained a predominant hybridizing band of the mobility predicted for the cDNA
plus vector sequences. No hybridization of connexin
probes was detected in cells transfected with the vector
alone.
Clones testing positive for connexin expression were
examined for the production of functional coupling
using the double whole-cell recording technique.5 Electrical communication was evident in 30-60% of the
pairs examined from each clone. Junctional conductance (gj) averaged 6.22±1.13 nS (mean±SEM, n=10)
for Cx42-transfected cell pairs, 3.38±0.79 nS (n=7) for
Cx43-transfected pairs, and 3.55±0.98 nS (n=16) for
Cx45-transfected pairs. The external application of
pharmacological uncouplers, 1 mM 1-octanol or 2 mM
1-heptanol, reversibly inhibited gj by >95% for all three
connexins (n-7, 7, and 12 pairs). Some cell pairs that
were obtained exhibited low levels (< 1 nS) of gj without
the addition of pharmacological uncoupling agents.
Brief examples of the Ij activity obtained from representative experiments for all three connexins are illus-
Veenstra et al Expression of Chick Heart Connexins
Cx42
A
-7 5
1279
B
c)
1-
z
12
0
a
IL
0
11
[C
m
z
JUNCTIONAL CURRENT (pA)
C
Cx43
|~
f open
D
V.=80mV
cD
1-
s2
WMf1
Z
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12
0-
11
W
0
IL
o
100-
m
20
pA
500 mSEC
1U
20
JUNCTIONAL CURRENT (pA)
E
Cx45
4
12
0-
-4-1-
F
iopen
^
1
x6
11
0
[L
0
U.
"I~ ~ ~ [
C
z
60
pA
500 mSEC
0
4
8
12
16 20
JUNCTIONAL CURRENT (pA)
FIGURE 2. Junctional channel currents obtained from connexin cDNA-transfected neuro2A (N2A) cellpairs. Panels A, C, and
E illustrate the paired whole-cell currents (I, and I2) obtained during a transjunctional voltage (Vj) pulse to the indicated value
for each connexin. In all three cases, the I2 tracing represents the junctional current (Ij) signal, and quantal fluctuations in the
upward direction of the I2 tracing (which are mirrored in the I, tracing) represent channel openings. The corresponding channel
amplitude histograms are shown in panels B, D, and Ffor each connexin. Correspondingpeaks in each histogram to the displayed
channel activity are labeled accordingly.1-5 Paired whole-cell currents (left column) were recorded from the onset of a >20-second
VJ pulse applied to one pair from each of the connexin cDNA-transfected N2A cell clones. The break in the connexin42 (Cx42)
tracings represents an 8-second gap in the channel recording. All current tracings were low-pass-filtered at 125 Hz and digitized at
1 kHz. Channel amplitude histograms compiledfrom the entire 20-second Ij recordings are shown in the right column. The area under
each peak is proportional to the time spent in each state. Channel events were counted by setting threshold detectors to the valley
between adjacent peaks and rescanning the digitized I2 tracing. Only those transitions having a duration of >1 msec were counted
as channel events. Only those peaks produced by more than two events or 2% of the total dwell time were used in determining channel
amplitudes. Numbers of channel events were 44, 38, and 45 for Cx42, connexin43 (Cx43), and connexin45 (Cx45), respectively.
trated in Figure 2, where unitary conductances of 163
and 195 pS for Cx42, 40-49 pS for Cx43, and 22-31 pS
for Cx45 were observed. Gap junction channel activity
was resolved in a total of six Cx42-transfected cell pairs,
three Cx43-transfected cell pairs, and four Cx45-transfected cell pairs. These results are summarized in Table
1. The predominant conductances for each connexin
were observed in all cell pairs examined and measured
1280
Circulation Research Vol 71, No 5 November 1992
TABLE 1. Channel Conductances of the Chick Heart Connexins
No. of transitions
No. of pairs
g1 (pS)
83
3 of 6
236+14
Cx42
201+11
52
3of6
442
6 of 6
158±10
261
5of6
121±8
25
3 of 6
86±3
55
67+6
1 of 3
Cx43
3 of 3
243
44+6
42
1 of 3
28±4
254
4
of 4
29+5
Cx45
gj, Mean±SD junctional conductance; Cx42, connexin42 (six
pairs total, transjunctional voltage of 40 mV, cumulative recording
time of 400 seconds); Cx43, connexin43 (three pairs total, transjunctional voltage of 80 mV, cumulative recording time of 71
seconds); Cx45, connexin45 (four pairs total, transjunctional voltage of 100 mV, cumulative recording time of 78 seconds).
Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017
158±+10 pS for Cx42, 44±5 pS for Cx43, and 29±5 pS
for Cx45. Mean±SD conductances for each connexin
were calculated by averaging the channel amplitudes
and event counts (determined as shown in Figure 2)
from all experiments. To illustrate the frequency and
amplitude distribution of all channel events reported in
Table 1, an event histogram was constructed (Figure 3).
Channel activity was clustered around a mean of 30 pS
for Cx45 and 45 pS for Cx43. Over 80% of the Cx42
channel activity was clustered around two distinct peaks
near 120 and 160 pS. Additional channel activity of
approximately 30 and 70 pS was observed in only one
Cx43 cell pair, and 5-10% of the cumulative Cx42
channel activity, distributed around each peak of 80,
205, and 230 pS, was observed in 50% of the cell pairs.
These findings are consistent with the hypothesis that
Cx42 forms the large 160-pS channel frequently observed in paired embryonic chick myocytes.5,24-26 The
multiple channel conductances observed in embryonic
chick heart (approximately 40, 80, 120, 160, 200, and 240
PS; see Reference 26) can be largely attributed to the
presence of Cx42, but the presence of one or both of the
other connexins may also account for some of the
smaller (<80 pS) channel activity observed in the
embryonic chick myocyte preparation. It is still unclear
whether the multiple channel conductances formed
from an individual connexin are the result of cooperative gating of small groups of channels having a single
unitary conductance, substates of a single large conductance channel, or some other biochemical modification
(e.g., phosphorylation) of the connexin proteins.26,27
Many gap junctions are modulated by Vj.1-7 28 In chick
heart, transjunctional potentials of ± 100 mV produced
a much greater reduction in g& in 4-day embryonic heart
than in 18-day heart.7 To examine the Vj sensitivity of gj
for the individually expressed connexins, Vj pulses were
applied to paired connexin-transfected N2A cells as
previously described.3,5 Instantaneous and steady-state
ljs were measured from the first and last 10 msec of each
Vj pulse, and Ij-Vj relations were determined for each
experiment. In all experiments, the instantaneous lI-Vi
relation (not shown) was approximated by a straight
line, indicating that the connexin-induced gap junctions
initially behave as ohmic resistors. This finding is consistent with similar observations obtained from embry-
80 -
40 0
80
Cx42
I
120 -
_.
1..
1.
UJL
^.I.
-
Cx43
I
0
.0 40
-
"II
;m
0-m
z
..................x4
...
...
80
:1 II
.
20 40
Cx45
..
..
A..
60
. ..1.....
80 100
1.
......
140
.
..
. . ..
180
. .
.
. . .
A.
.
220
Channel Conductance (pS)
FIGURE 3. Channel amplitude event histograms. The event
frequency histograms for all 863, 340, and 254 channel events
for the connexin42 (Cx42) -, connexin43 (Cx43) -, and connexin45 (Cx45) -transfected cell pairs presented in Table 1
were plotted relative to their conductance amplitudes (5-pS
bin width). The histogram shows distinct peaks of 120 and
160 pS for Cx42, 45 and 70 pS for Cx43, and 30pS for Cx45.
Less abundant channel activity was observed near 80, 205,
and 230 pS for Cx42 and 30 pS for Cx43. The amplitudes for
all three connexins were plotted on the same scale for comparison of the relative conductance amplitudes.
onic chick heart.5'7 Steady-state Ij-Vj relations were
nonlinear for all experiments, although the magnitude
of the steady-state decrease in Ij was different for each
of the connexins examined. To illustrate these differences, the steady-state gj was normalized to the instantaneous gj of each pulse, and resulting normalized
steady-state junctional conductance (GSS) was plotted as
a function of Vj for each experiment. The average
steady-state Ij-Vj relation for each connexin is illustrated in Figure 4. Cx45 was the only cardiac connexin
to undergo a significant reduction (>10%) in GQ, at low
Vj values ( ±20 mV). G,, declined by >10% in Cx42transfected pairs only when Vj exceeded ±20 mV, and
similar reductions in GSS did not occur in Cx43-transfected pairs until Vj exceeded ±50 mV. The minimum
steady-state junctional conductance (Gfi..) at ± 100 mV
showed a similar relation, with Cx45 having the smallest
experimental GQ,, of 0.11, Cx42 was intermediate with a
G,,,, of 0.36, and Cx43 achieved a Gfi, of 0.62 at + 100
mV. The Gc-Vj curve for each connexin was mathematically represented by the two-state Boltzmann relation
used to describe other Vj-dependent gap junctions5-7 26 28
(Figure 4, Table 2). According to this analysis, the most
distinguishing features for each curve are the low minimum G,, for Cx45 and the large half-inactivation voltage
Veenstra et al Expression of Chick Heart Connexins
TABLE 2. Parameters of the Voltage Dependence of Chick
Connexin and Chick Heart Gap Junctions
A
V0 (mV)
Preparation No. of pairs
Gmin
0.38+0.02 0.108±0.007 41±1
10
Cx42
77±4
0.53+0.05 0.064±0.008
Cx43
7
0.09±0.04 0.055±0.006 39±2
16
Cx45
0.18±0.05 0.058±0.006 42±2
8
4-Day heart
0.36±0.04 0.100±0.010 52±2
11
18-Day heart
Cx42
100
Cx43
Gss
1.1
]E
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U.5
.
-100
.
.
.
.
.
-50
.
.
.
.
.
50
100
Cx45
-100
-50
0
1281
50
100
Transjunctional Voltage (mV)
FIGURE 4. Boltzmann relations for embryonic chick cardiac
connexin42 (Cx42), connexin43 (Cx43), and connexin45
(Cx45). The filled square and error bars represent the
mean+±SEM steady-state junctional conductance/instantaneous junctional conductance (GSS) for each of the indicated
connexins. The G,,-transjunctional voltage (Vj) relation for
each connexin was fitted with a theoretical line determined by
the Boltzmann relation: Gss=(1 -Gm.m)I{1 +exp[A(Vj-Vo)]}
+Gmm, where Gmin is the voltage-insensitive component of G,,,
VO is the half-inactivation voltage for the voltage-sensitive
component of G,,, and A is the slope factor expressing the
charge sensitivity of the transition between the high and low
conductance states. A is determined by the expression zq/kT,
where z is the number of equivalent electrons q, k is Boltzmann's constant, and T is absolute temperature. The values
for the relevant parameters are listed in Table 2.
for Cx43. The Cx42 G,S-Vj curve has the steepest slope of
the three, indicative of a higher charge sensitivity to
changes in Vj.
Gmin, minimum steady-state junctional conductance; A, slope
factor; V0, half-inactivation voltage; Cx42, connexin42; Cx43,
connexin43; Cx45, connexin45. Values are mean±1 SD of the
mean for the fitted curve.
Values were calculated for the theoretical fit to the Boltzmann
relation shown in Figure 3. Data for embryonic chick heart gap
junctions are from Reference 5. The Gmin calculated for Cx43 is
9% lower than the experimental Gm.n. It appears that steady-state
junctional conductance had not stabilized at a true minimum value
within the range of transjunctional potentials used in these experiments. The least-squares fit of the data using the Boltzmann
equation extrapolated the existing data to provide an estimated
Gmin of 0.53 (transjunctional voltage of > ± 140 mV).
Channels formed from the individual connexins may
explain the voltage dependence previously observed in
embryonic chick heart gap junctions. Figure 5 compares
the Boltzmann curves for Cx45 and Cx42 with the data
obtained previously from 4-day and 18-day embryonic
ventricular myocyte pairs.7 The Boltzmann parameters
for developing heart are also listed in Table 2. Although
not identical, the Cx45 curve closely approximates that
of 4-day heart, whereas the Cx42 curve is similar to that
of 18-day heart. These observations support the hypothesis that intercellular communication in the developing
chick heart is formed predominantly by Cx45 in the
early embryo and by Cx42 in later stages of embryonic
(and adult) development.
Discussion
This study demonstrates that the three connexins
expressed in the heart, Cx42, Cx43, and Cx45, all form
functional gap junctional channels. However, the gap
junctions derived from expressing each of the three
proteins in the same system have different conductance
and regulatory properties. These observations confirm
previous speculations that sequence differences between connexins might produce physiological differences. Although the exact regions in the connexin
molecules responsible for any biophysical properties
have not been determined, the major differences between connexins lie in two cytoplasmic regions.8
The biophysical characteristics associated with each
connexin are sufficient to explain the observations made
in the previous electrophysiological examinations of gap
junctional channels between cardiac myocytes. Our
results indicate that Cx42 forms the predominant
160-pS channel and many of the other less frequently
observed channel conductances found in embryonic
chick heart (Table 1, References 5 and 24-26), whereas
Cx43 and Cx45 form channels of <80 pS in amplitude,
which are rarely resolved in chick heart cells. The
10-fold decline in expression of Cx45 mRNA between
6-day embryonic and adult heart16 appears to explain
developmental changes in voltage dependence.7 The
Boltzmann curves show that 4-day heart has similar
characteristics to Cx45 -expressing cells, whereas 18-day
1282
Circulation Research Vol 71, No 5 November 1992
FIGURE 5. Comparison ofBoltzmann relations
of chick connexin42 (Cx42) and connexin45
(Cx45) to developing heart. Ge,, steady-state
junctional conductance. The Boltzmann curves
for Cx42, Cx45, 4-day embryonic, and 18-day
embryonic chick heart are displayed together to
emphasize the similarities between the expressed
connexins and the developing heart. The values
for the Boltzmann parameters can be found in
Table 2.
-100
-50
0
Transjunctional
50
100
Voltage (mV)
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heart has characteristics similar to the major connexin
at that age, Cx42.
The data suggest that gap junction electrophysiology
is more closely related to which connexin is expressed
than to species-specific differences in a single connexin.
Previous studies had suggested that avian and mammalian cardiac gap junction proteins were quite different.
Those studies had shown that chick embryo ventricular
myocytes contain predominantly a 160-pS channel and
some smaller conductances, whereas channels between
mammalian heart cells have a conductance of =50
pS.3-5,24-26 Our previous data showed that Cx42 is the
most abundant connexin expressed in chick embryo
heart but that Cx43 predominates in mammalian
heart.1617 El Aoumari et a129 could detect abundant
immunoreactive Cx43 in many mammalian, but not
chicken, hearts. Those results predicted that Cx42 must
form the chick 160-pS channel, whereas Cx43 forms the
mammalian 50-pS channel, as confirmed by expression
studies. Functional differences between the chick and
mammalian homologues of Cx43 appear to be relatively
minor, based on the similar observations of a 50-pS
channel conductance and weak Vj sensitivity (halfinactivation voltage, > +40 mV; Gmin, >0.40) of both
connexins expressed in transfected SKHepl cells.1430
The differences in unitary conductance and voltage
dependence may not be the only differences between
connexins. No one has yet examined several other properties that may also be physiologically important. These
channels might differ in their responses to protein kinases and second messenger cascades or might have
different permeabilities to ions and small molecules. It is
also possible that one connexin has a greater propensity
for posttranslational modification (e.g., phosphorylation), which might contribute to differences in regulation,
conductance, or voltage dependence. For example, tyrosine phosphorylation of rat Cx43, but not rat Cx32, by
viral src gene protein tyrosine kinase (pp60v-s'C) induces
inhibition of junctional communication.3' The expression
of multiple connexins within the same tissue raises many
new questions about the diversity of gap junction physiology that may result if distinct connexins can mix within
a single hemichannel or channel. It is also possible that
additional cardiac connexins may be discovered in the
future.
The physiologically different channels derived from
multiple connexins may have important implications in
the mature as well as in the developing heart. We
recently demonstrated that adult canine cardiac ventricular myocytes contain connexins homologous to chick
Cx42, Cx43, and Cx45.17 We are currently examining
the abundance and distribution of these connexins
within the adult heart. The three connexins derive from
distinct genes; therefore, modulation of gene expression
of the connexins may differ. Differential connexin expression may confer multiple mechanisms of regulating
junctional communication within the normal and diseased heart.
Acknowledgments
We thank M. Chilton for his assistance in maintaining the
clonal N2A cell cultures.
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Multiple connexins confer distinct regulatory and conductance properties of gap junctions
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R D Veenstra, H Z Wang, E M Westphale and E C Beyer
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Circ Res. 1992;71:1277-1283
doi: 10.1161/01.RES.71.5.1277
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