Published November 24, 2014
Combined effects of fungal alkaloids on intestinal motility in an in vitro rat model1,2
J. E. Dalziel,*3 K. E. Dunstan,* and S. C. Finch†
*Food Nutrition and Health Team, Food & Bio-based Products Group, AgResearch, Grasslands
Research Centre, Private Bag 11008, Palmerston North 4442, New Zealand; and †Plant-fungal Interactions Team,
Forage Improvement Group, AgResearch Ruakura Research Centre, Private Bag 3123, Hamilton 3240, New Zealand
ABSTRACT: Diarrhea is caused by factors that alter
absorption and secretion of water and ions across
the intestinal epithelium and disrupt motility. Parasitic infection, stress, poor nutrition, and exposure to
plant or fungal toxins predispose livestock to noninfectious diarrhea. This is more prevalent in sheep that
graze pastures infected with wild-type endophytic fungus, suggesting the involvement of fungal alkaloids.
These increase smooth muscle contraction: ergovaline/
ergotamine (ergot alkaloid) activates serotonin (5-HT)
receptors, and lolitrem B (indole diterpene) inhibits
large-conductance Ca2+–activated K+ (BK) channels. Because of their separate mechanisms of action
the objective of this study was to investigate whether they act synergistically to increase smooth muscle
contraction. Effects of ergotamine (1 µM) and lolitrem
B (0.1 µM) on the tension and frequency of sponta-
neous contractions were investigated in a longitudinal
preparation of isolated distal colon. The compounds
were dissolved in 0.1% dimethyl sulfoxide (DMSO)
and applied separately or together for 1 h. Ergotamine
increased contractile tension compared to the pretreatment control (P < 0.01) and produced a short-lived
increase in frequency (P < 0.001). Lolitrem B increased
contractile tension (P < 0.05) but had no effect on frequency. When applied together, the contractile tension
was greater than the sum of the compounds applied
separately (P < 0.05). The frequency of contractions
was increased (P < 0.05) but was not significantly different from that for ergotamine alone. The increased
contractile tension when both compounds were applied
together indicates that ergotamine and lolitrem B acted
synergistically to increase smooth muscle contraction,
suggesting that they would alter motility in vivo.
Key words: ergot alkaloid, fungal toxin, intestinal motility, ion channel, lolitrem B, smooth muscle
© 2013 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2013.91:5177–5182
doi:10.2527/jas2013-6449
Introduction
Endophytic fungi confer increased insect pest
resistance to perennial ryegrass in pastures through
production of beneficial metabolites. However,
the naturally occurring wild-type endophyte
(Neotyphodium lolii) also produces compounds
that are detrimental to animal health. Lolitrem B,
an indole diterpene, is the main causative agent of
a tremor syndrome of grazing animals known as
1This
work was supported by a grant from the Curiosity Fund,
AgResearch, New Zealand.
2We thank Ric Broadhurst and Bobby Smith for animal breeding
and Hailey Gillespie for animal care. We thank Jonathan Simpson for
assistance with data analysis and Catherine Lloyd-West for statistical
analysis.
3Corresponding author: [email protected]
Received March 6, 2013.
Accepted August 5, 2013.
ryegrass staggers (Gallagher et al., 1981). Ergovaline,
an ergot alkaloid, is associated with detrimental
thermal stress responses in livestock (Strickland et al.,
1993). In addition to the well-described deleterious
physiological impacts of wild-type endophyte on
animal production, it has also been observed that
gastrointestinal tract associated problems are more
common than for animals on nil-endophyte pastures.
A field report noted that lambs grazing wild-type
endophyte pastures had a 2- to 4-fold greater incidence
of dags (dried feces adhered to hind quarter wool)
compared with animals on nil-endophyte pastures
(Fletcher et al., 1999). The association between
endophyte toxins and dags is not understood. Both
lolitrem B and ergovaline reach the intestine because
they appear in the feces after ingestion in sheep
(De Lorme et al., 2007; Cripps and Edwards, 2013).
Previous studies have shown that ergot alkaloids
5177
5178
Dalziel et al.
(McLeay and Smith, 2006; Poole et al., 2009) and
indole diterpenes (Smith et al., 1997; McLeay et al.,
1999; McLeay and Smith, 2006) affect smooth muscle
contraction in sheep. Indole diterpenes, including
lolitrem B, increase intestinal motility (DeFarias et
al., 1996; Wang et al., 2003) and inhibit K+ channels
(BK; Dalziel et al., 2005). The BK channel is highly
expressed in smooth muscle (Knaus et al., 1995),
including the colon (Sausbier et al., 2006), and are
important for motility in the rat distal colon (France
et al., 2012). The ability of ergot alkaloids to increase
smooth muscle contraction via serotonin receptors is
well described in the digestive tract (Franhuijzen, 1975;
Radulovic et al., 1984) and in blood vessels (Muller
Schweinitzer, 1983; MacLennan and Martin, 1990;
Dyer, 1993; Klotz et al., 2009).
The fact that lolitrem B and ergovaline are found
together in wild-type endophyte and both increase
smooth muscle contraction in vitro through separate
mechanisms led us to investigate whether they might act
synergistically to increase smooth muscle contraction.
We used a rat model of colon function because it
produces similar responses to those in sheep tissue for
these compounds (Franhuijzen, 1975; Wang et al., 2003;
Poole et al., 2009) and because these are naive animals.
Materials and Methods
This research was approved by the AgResearch
Grasslands Animal Ethics Committee, established
under the Animal Protection (Code of Ethical Conduct)
Regulations Act, 1987 (New Zealand). Animals were
killed by CO2 inhalation. Three to four animals were
used per experiment with duplicate preparations per
animal. Methods were adapted from those described
elsewhere for rat distal colon (Brighton et al., 2008;
Gursoy et al., 2008; Jeong et al., 2009).
Isolation of Rat Colon
Male Sprague Dawley rats (7–12 wk of age)
obtained from AgResearch Ruakura (Hamilton, NZ)
were housed under a 12-h light/dark cycle and were fed
Sharpes Diet 86 (Sharpes Stockfeeds Ltd., Carterton,
New Zealand). After euthanasia, a 2-cm piece of distal
colon was removed 1 cm distal to the striations of the mid
colon. The tissue was placed in Kreb’s buffer (118 mM
NaCl, 4.7 mM KCl, 1.2 mM KH2PO4, 1.2 mM MgSO4,
2.6 mM CaCl2, 25 mM NaHCO3, 11 mM glucose, pH
7.4) oxygenated with 95% O2/5% CO2. The preparation
was divided in half, and two distal colon pieces were
mounted longitudinally on holders in an isolated tissue
bath system (SI-MB4, SI-Heidelberg, World Precision
Instruments, Sarasota, FL) at 37°C.
Muscle Contractile Measurements
Tissues were suspended under 1 g of tension and
equilibrated for 1 h in Krebs buffer during which time
the bath solution was exchanged every 15 min. Control
spontaneous muscle contractions were measured
during the last 15 min of a 1-h exposure to 0.1%
dimethyl sulfoxide (DMSO) and compared with the
response to the test compounds applied separately or
in combination over 1 h. Ergotamine tartrate (1 µM)
and lolitrem B (0.1 µM) were dissolved in DMSO
and applied directly to the baths in a 1/10 dilution and
reapplied every 15 min with the new bath solution
(final DMSO concentration in bath of 0.1%). Muscle
contraction data were measured using BAM21-E
amplifiers integrated using Lab-Trax 4/24T hardware
and acquired and analyzed using Labscribe 2 software
(iWorx Inc., Dover, NH). Data from the last 10 min
of a 15-min recording period were analyzed, and the
mean for each parameter was determined from the
contractile responses recorded. Contractile tension or
amplitude (g) was measured from the baseline to the
maximum peak of the contractile response. Contractile
frequency was measured as the number of contractions
counted per min. The maximum tension response was
compared to that for 1 µM acetylcholine (Sigma, St.
Louis, MO), and preparations that gave little or no
response were excluded. The response to tetrodotoxin,
a neuronal voltage-gated sodium channel inhibitor
(Alomone Labs, Jerusalem, Israel), was also assessed
in spontaneously contracting preparations.
Toxins
Lolitrem B was extracted from ryegrass seed infected
with Neotyphodium lolii and purified by chemical
methods as previously described (Miles et al., 1994). A
concentration of 0.1 µM lolitrem B was used because this
concentration had the greatest effect in a concentrationresponse experiment (Suppl. Fig. 1; see online version
of the article at http://journalofanimalscience.org) and
maximally inhibits BK ion channels in vitro (Dalziel et
al., 2005; Imlach et al., 2008).
Because of difficulty in obtaining sufficient
quantities of ergovaline, the structurally related
compound ergotamine was used instead. Ergotamine
tartrate (Sigma Chemical Company, St Louis, MO)
was used at a concentration of 1 µM ergotamine
because this concentration had the greatest effect in
a concentration-response experiment (Suppl. Fig. 1)
and has shown effects in vitro in previous studies
(Franhuijzen, 1975; Poole et al., 2009). Ergotamine
has time-dependent and pre-exposure effects that are
well described (Klotz et al., 2009). The effects of both
compounds are not reversible in the time frame of an
5179
Fungal alkaloids alter intestinal motility
in vitro experiment (Dalziel et al., 2005; Poole et al.,
2009); therefore, each tissue preparation was used for
only one treatment.
Statistical Analysis. Results are expressed as
the mean ± SEM from ≥5 preparations (from ≥3
animals). Statistical comparisons were made using
GenStat version 12.2 (VSN International Ltd., Hemel
Hempstead, UK). Analysis of variance was used on
repeated measurements to compare treatment effects
over time. To compare between treatments, time was
treated as a covariate.
Results
Spontaneous contractions were measured in the
rat distal colon in vitro, and effects of lolitrem B and
ergotamine compared, alone or in combination, on
contractile tension and frequency. To determine the
origin of the spontaneous contractions recorded from
the 1 cm segments of isolated rat distal colon, 1 µM
tetrodotoxin was applied to inhibit the neuronal voltagegated sodium channels. Tetrodotoxin did not inhibit the
spontaneous phasic contractions (n = 3), indicating that
they were not initiated by enteric neurons.
Spontaneous contractile activity recorded from the
isolated distal colon before and after addition of each
compound is shown in Figs. 1a, 1b, and 1c. The effect of
each treatment on spontaneous muscle contractions was
measured relative to that in the 60 min control recording
in Krebs with 0.1% DMSO (Jeong et al., 2009). Data
comparing the effect of each treatment on contractile
tension and frequency are shown in Figs. 2a and 2b.
To account for variation in contractile activity among
preparations, pretreatment controls were standardized to
1.0, and the effect of a treatment was determined as a
difference from the control.
Lolitrem B increased the contractile tension
after 60 min of exposure (Fig. 2a) but had no effect
on frequency (Fig. 2b). Ergotamine increased peak
contractile tension (Fig. 2a) at all time points over the 60
min exposure period. The frequency of contractions was
also increased over this time, but the effect was greatest
in the first 15 min (Fig. 2b). Coapplication of lolitrem B
and ergotamine greatly increased the contractile tension
over 60 min of exposure (Fig. 2a). The magnitude of
the increase in peak tension for the compounds in
combination (1.35 g) was greater than the sum of the
effect for each compound alone (0.90 g). The frequency
of contractions was also significantly increased 15 min
after application of both compounds but decreased on
continued exposure and was not significantly different
from the control at 60 min (Fig. 2b). All three treatment
conditions were also able to induce contractions in
quiescent preparations.
Discussion
The data indicate that the main effect of lolitrem B
on the rat distal colon was to increase muscle tension,
which occurred slowly over 1 h. This is the first report
of lolitrem B affecting muscle contraction in the
rat distal colon. This finding is consistent with that
observed in the isolated sheep reticulorumen, where the
same concentration of lolitrem B increased electrically
stimulated contractions with 12 min of latency and the
effect recorded over 30–60 min thereafter (Wang et al.,
2003). This supports the rat distal colon as a suitable
small animal model for sheep.
In contrast to lolitrem B, ergotamine induced a
rapid increase in contractile tension and frequency of
contraction. This is the first time an effect of ergotamine
on frequency of contraction has been reported. Previous
studies have used electrical stimulation protocols to
induce the muscle to contract at a given frequency rather
than measuring changes in spontaneous contractions.
Ergotamine (and ergovaline) does, however, initiate
spontaneous contractions in previously quiescent
isolated sheep reticulum preparations (Poole et al.,
2009), as we also observed for the rat colon. An effect
on frequency as well as tension is relevant in the context
of the endophyte alkaloids because it shows differences
between the two classes of compound. This result is
consistent with effects of serotonin agonist drugs that
increase gastrointestinal motility via specific serotonin
(5HT) receptor subtypes (5HT2B, 5HT2C, 5HT3, and
5HT4) in humans.
When both toxins are applied together, the large
increase in contractile tension compared with the sum
of either applied alone was the most marked effect.
This indicates that when the distal colon is exposed to
both lolitrem B and ergotamine, the two compounds
acted synergistically to increase contractile tension. It
can be speculated that the mechanisms underlying
this effect might involve calcium because ergotamine
activation of serotonin receptors would be expected to
increase intracellular calcium levels (via GPCR and IP3
pathways or calcium-permeable 5-HT3 ion channels)
and BK channels are known to be activated by calcium
released from IP3 receptor–operated stores in murine
colonic muscle (Bayguinov et al., 2000). Ergovaline/
ergotamine (ergot alkaloid) activates serotonin (5HT) receptors, leading to an increase in intracellular
calcium, and lolitrem B (indole diterpene) inhibits
large-conductance Ca2+–activated K+ channels that
are activated by intracellular calcium and depolarizing
membrane voltages. Although the mechanism of action
of this effect is different for the ergot alkaloids and
lolitrem B, both mechanisms involve calcium.
5180
Dalziel et al.
Figure 1. Effect of endophyte compounds on spontaneous muscle contraction in the isolated rat distal colon. Examples of raw data recordings show changes
in muscle tension over time for the control (0.1% dimethyl sulfoxide [DMSO]) and after addition of (a) 0.1 µM lolitrem B (LB), (b) 1 µM ergotamine (Erg), or
(c) 0.1 µM lolitrem B and 1 µM ergotamine (LB + Erg).
The BK ion channels are considered to have an
important role in smooth muscle function in that they
provide a safety mechanism to dampen excitation during
times of high muscle or nerve activity. When activated by
internal calcium and positive membrane potentials, BK
channels allow K+ ions to flow out of the cell, keeping the
membrane potential closer to the resting potential. The
BK channels appear to regulate the membrane potential
in the mouse distal colon (France et al., 2012). When both
ergotamine and lolitrem B are applied to colonic smooth
muscle together, the anticipated increase in calcium
mobilization due to serotonin receptor activation caused
by ergotamine would be expected to increase muscle
activity. Inhibition by lolitrem B resulting in removal
of the safety mechanism in regulating the membrane
potential that BK channels normally provide would
make it more likely that action potential firing will occur,
leading to a further increase in muscle contraction.
The increased intestinal motility observed in response
to a combination of endophyte alkaloids in this rat model
suggests that in vivo gastrointestinal motility would
be disrupted after dietary exposure to lolitrem B and
ergovaline at concentrations in the range that may be
ingested from wild-type endophyte-infected perennial
ryegrass (De Lorme et al., 2007; Reed et al., 2011; Cripps
and Edwards, 2013). This effect is consistent with the
5181
Fungal alkaloids alter intestinal motility
It is interesting to note that physiological effects of
ergot alkaloids (serotonin agonists) on animals described
by “tall fescue toxicosis syndrome” share symptoms
in common with the clinical condition of “serotonin
syndrome” in humans, including hyperthermia,
hypertension, and hyperactive bowel (diarrhea; Boyer
and Shannon, 2005). Serotonin syndrome occurs when
serotonin receptors are overstimulated by agonists or
excess serotonin release, as a consequence of taking
more than one serotonergic medication (Birmes et al.,
2003; Boyer and Shannon, 2005). It is possible that
ingestion of other compounds that affect serotonin
receptors through endophyte, other fungi, or plants
might exacerbate the effects of ergotamine and lolitrem
B to further increase intestinal motility.
The findings of this study indicate that ergot alkaloids
and indole diterpenes can act in a synergistic manner
to increase smooth muscle contractility in mammalian
intestinal tissue. This suggests that increased intestinal
motility may occur in animals that ingest wild-type
endophyte-infected grass containing a mixture of these
compounds and other structurally related alkaloids and
could contribute to the diarrhea observed in animals
grazing these pastures.
Literature Cited
Figure 2. Summary of endophyte compound effects on contractile
parameters of spontaneous muscle contraction in the isolated rat distal colon.
Changes in (a) tension (g) and (b) frequency (number of contractions per
min) were averaged over the preceding 10 min for each time point. The
effect of treatments is shown as a difference relative to the control (0.1%
dimethyl sulfoxide [DMSO]). Treatments were applied for 1 h each for either
0.1 µM lolitrem B (circles; n = 5), 1 µM ergotamine (squares; n = 7), or both
(triangles; n = 6). Significance was tested using repeated measures analysis
of variance to compare treatment effects over time. To compare between
treatments, time was treated as a covariate. Asterisks indicate the significance
of each treatment relative to controls or between treatments as indicated (*P <
0.05; **P < 0.01, ***P < 0.001). Data show mean ± SEM.
intestinal dysfunction that occurs in diarrhea/scouring
and subsequent dags observed in sheep grazing wildtype endophyte-infected pastures (Fletcher et al., 1999).
Additional structurally related ergopeptide and indole
diterpene compounds produced by endophytes, which
activate 5-HT receptors and inhibit BK channels (Imlach et
al., 2009), respectively, are likely to contribute to increased
motility. It remains to be determined whether lolitrem B and
ergotamine affect ion secretion in the colon to produce the
increased fecal moisture that occurs in dags and subsequent
fly-strike (fly larvae in wool of hindquarters). Furthermore,
the urinary incontinence that occurs in mice lacking BK ion
channels (Meredith et al., 2004) suggests that inhibition of
BK channels by lolitrem B might produce a similar effect
in sheep, exacerbating the probability of fly-strike.
Bayguinov, O., B. Hagen, A. D. Bonev, M. T. Nelson, and K. M.
Sanders. 2000. Intracellular calcium events activated by ATP
in murine colonic myocytes. Am. J. Physiol. Cell Physiol.
279:C126–C135.
Birmes, P., D. Coppin, L. Schmitt, and D. Lauque. 2003. Serotonin
syndrome: A brief review. Can. Med. Assoc. J. 168:1439–1442.
Boyer, E. W., and M. Shannon. 2005. Current concepts: The serotonin
syndrome. N. Engl. J. Med. 352:1112–1120.
Brighton, P. J., A. Wise, N. B. Dass, and G. B. Willars. 2008.
Paradoxical behavior of neuromedin U in isolated smooth muscle
cells and intact tissue. J. Pharmacol. Exp. Ther. 325:154–164.
Cripps, M. G., and G. R. Edwards. 2013. Fungal endophytes of a forage
grass reduce faecal degradation rates. Basic Appl. Ecol. 14:146–154.
Dalziel, J. E., S. C. Finch, and J. Dunlop. 2005. The fungal neurotoxin
lolitrem B inhibits the function of human large conductance
calcium-activated potassium channels. Toxicol. Lett. 155:421–426.
DeFarias, F. P., M. F. Carvalho, S. H. Lee, G. J. Kaczorowski, and
G. Suarez-Kurtz. 1996. Effects of the K+ channel blockers
paspalitrem-C and paxilline on mammalian smooth muscle. Eur.
J. Pharmacol. 314:123–128.
De Lorme, M. J. M., S. L. Lodge-Ivey, and A. M. Craig. 2007.
Physiological and digestive effects of Neotyphodium coenophialuminfected tall fescue fed to lambs. J. Anim. Sci. 85:1199–1206.
Dyer, D. C. 1993. Evidence that ergovaline acts on serotonin
receptors. Life Sci. 53:PL223–PL228.
Fletcher, L. R., B. L. Sutherland, and C. G. Fletcher. 1999. The impact
of endophyte on the health and productivity of sheep grazing
ryegrass-based pastures. Grasslands Res. Pract. Ser. 7:11–17.
France, M., Y. Bhattarai, J. J. Galligan, and H. Xu. 2012. Impaired
propulsive motility in the distal but not proximal colon of BK
channel β1-subunit knockout mice. Neurogastroenterol. Motil.
24:e450–e459.
5182
Dalziel et al.
Franhuijzen, A. L. 1975. Analysis of ergotamine-5HT interaction on the
isolated rat stomach preparation. Eur. J. Pharmacol. 30:205–212.
Gallagher, R. T., E. P. White, and P. H. Mortimer. 1981. Ryegrass
staggers: Isolation of potent neurotoxins lolitrem A and lolitrem
B from staggers-producing pastures. N. Z. Vet. J. 29:189–190.
Gursoy, N., N. Durmus, I. Bagcivan, B. Sarac, A. Parlak, S. Yildirim,
and T. Kaya. 2008. Investigation of acute effects of aflatoxin on
rat proximal and distal colon spontaneous contractions. Food
Chem. Toxicol. 46:2876–2880.
Imlach, W. L., S. C. Finch, J. Dunlop, and J. E. Dalziel. 2009. Structural
determinants of lolitrems for inhibition of BK large conductance
Ca2+–activated K+ channels. Eur. J. Pharmacol. 605:36–45.
Imlach, W. L., S. C. Finch, J. Dunlop, A. L. Meredith, R. W. Aldrich,
and J. E. Dalziel. 2008. The molecular mechanism of “ryegrass
staggers” a neurological disorder of potassium channels. J.
Pharmacol. Exp. Ther. 327:657–664.
Jeong, S. I., Y. S. Kim, M. Y. Lee, J. K. Kang, S. Lee, B. K. Choi, and
K. Y. Jung. 2009. Regulation of contractile activity by magnolol in
the rat isolated gastrointestinal tracts. Pharmacol. Res. 59:183–188.
Klotz, J. L., B. H. Kirch, G. E. Aiken, L. P. Bush, and J. R. Strickland.
2009. Bioaccumulation of ergovaline in bovine lateral
saphenous veins in vitro. J. Anim. Sci. 87:2437–2447.
Knaus, H. G., A. Eberhart, R. O. A. Koch, P. Munujos, W. A.
Schmalhofer, J. W. Warmke, G. J. Kaczorowski, and M. L.
Garcia. 1995. Characterization of tissue-expressed α subunits of
the high conductance Ca2+–activated K+ channel. J. Biol. Chem.
270:22434–22439.
MacLennan, S. J., and G. R. Martin. 1990. Actions of non-peptide
ergot alkaloids at 5-HT1–like and 5-HT2 receptors mediating
vascular smooth muscle contraction. Naunyn Schmiedebergs
Arch. Pharmacol. 342:120–129.
McLeay, L. M., and B. L. Smith. 2006. Effects of ergotamine and
ergovaline on the electromyographic activity of smooth muscle
of the reticulum and rumen of sheep. Am. J. Vet. Res. 67:707–714.
McLeay, L. M., B. L. Smith, and S. C. Munday-Finch. 1999.
Tremorgenic mycotoxins paxilline, penitrem and lolitrem B, the
non-tremorgenic 31-epilolitrem B and electromyographic activity
of the reticulum and rumen of sheep. Res. Vet. Sci. 66:119–127.
Meredith, A. L., K. S. Thorneloe, M. E. Werner, M. T. Nelson, and
R. W. Aldrich. 2004. Overactive bladder and incontinence in
the absence of the BK large conductance Ca2+–activated K+
channel. J. Biol. Chem. 279:36746–36752.
Miles, C. O., S. C. Munday, A. L. Wilkins, R. M. Ede, and N. R.
Towers. 1994. Large-scale isolation of lolitrem B and structure
determination of lolitrem E. J. Agric. Food Chem. 42:1488–1492.
Muller Schweinitzer, E. 1983. Vascular effects of ergot alkaloids: A
study on human basilar arteries. Gen. Pharmacol. 14:95–102.
Poole, D. P., R. A. Littler, B. L. Smith, and L. M. McLeay. 2009.
Effects and mechanisms of action of the ergopeptides ergotamine
and ergovaline and the effects of peramine on reticulum motility
of sheep. Am. J. Vet. Res. 70:270–276.
Radulovic, S., N. Djordjevic, and T. Kazic. 1984. The effect of ergot
alkaloids ergosinine, dihydroergosine and dihydroergotamine
on neurotransmission and contractility of the isolated ileum of
the guinea-pig. J. Pharm. Pharmacol. 36:814–819.
Reed, K. F. M., Z. N. Nie, L. V. Walker, and G. Kearney. 2011. Fluctuations
in the concentration of ergovaline and lolium B produced by the
wild-type endophyte (Neotyphodium lolii) in perennial ryegrass
(Lolium perenne) pasture. Anim. Prod. Sci. 51:1098–1108.
Sausbier, M., J. E. Matos, U. Sausbier, G. Beranek, C. Arntz, W. Neuhuber,
P. Ruth, and J. Leipziger. 2006. Distal colonic K+ secretion occurs
via BK channels. J. Am. Soc. Nephrol. 17:1275–1282.
Smith, B. L., L. M. McLeay, and P. P. Embling. 1997. Effect of
the mycotoxins penitrem, paxilline and lolitrem B on the
electromyographic activity of skeletal and gastrointestinal
smooth muscle of sheep. Res. Vet. Sci. 62:111–116.
Strickland, J. R., J. W. Oliver, and D. L. Cross. 1993. Fescue
toxicosis and its impact on animal agriculture. Vet. Hum.
Toxicol. 35:454–464.
Wang, L., A. L. Cross, K. L. Allen, B. L. Smith, and L. M. McLeay. 2003.
Tremorgenic mycotoxins increase gastric smooth muscle activity
of sheep reticulum and rumen in vitro. Res. Vet. Sci. 74:93–100.