Intracellular microelectrode recording to characterize inhibitory neuromuscular transmission in jejunum of horses

Peter C. Rakestraw Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616
present address is Department of Large Animal Surgery and Medicine, Texas A&M University, College Station, TX 77843.

Search for other papers by Peter C. Rakestraw in
Current site
Google Scholar
PubMed
Close
 VMD
,
Jack R. Snyder Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616.

Search for other papers by Jack R. Snyder in
Current site
Google Scholar
PubMed
Close
 DVM, PhD
,
Kenton M. Sanders Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV 89557.

Search for other papers by Kenton M. Sanders in
Current site
Google Scholar
PubMed
Close
 PhD
, and
William C. Shuttleworth Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, NV 89557.
Department of Neurosciences, School of Medicine, University of New Mexico, Albuquerque, NM 87131.

Search for other papers by William C. Shuttleworth in
Current site
Google Scholar
PubMed
Close
 PhD

Click on author name to view affiliation information

Abstract

Objective—To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons.

Sample Population—Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease.

Procedure—Isolated circular muscle preparations were perfused with oxygenated modified Krebs solution. Glass microelectrodes were used for intracellular recording of membrane potentials from single smooth muscle cells. Electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence of guanethidine and atropine were recorded. Mediators of responses to nerve stimulation were also evaluated, using N-nitro-L-arginine methyl ester (L-NAME) and apamin.

Results—Mean resting membrane potential (RMP) was 41.5 ± 1.8 mV. Small membrane potential oscillations were observed in muscle cells. Single or multiple action potentials were often superimposed on the peaks of these oscillations. Spontaneous oscillations and action potentials were blocked by nifedipine. Transient hyperpolarizations of smooth muscle cell membrane potentials (inhibitory junction potentials [IJP]) were observed in response to electrical field stimulation. The IJP evoked by stimulus trains consisted of an initial fast component followed by a slow component. The L-NAME did not have a significant effect on RMP and did not significantly affect the fast component of IJP at any stimulus frequency tested. In contrast, L-NAME abolished the slow component of IJP observed after trains of pulses. In the continued presence of L-NAME, apamin had no significant effect on RMP but effectively reduced the fast component of IJP.

Conclusions and Clinical Relevance—Findings suggest that inhibitory neurotransmitters supplying equine jejunum act through different ionic mechanisms. Understanding these mechanisms may suggest new therapeutic targets for treatment of motility disorders. (Am J Vet Res 2000;61:362–368)

Abstract

Objective—To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons.

Sample Population—Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease.

Procedure—Isolated circular muscle preparations were perfused with oxygenated modified Krebs solution. Glass microelectrodes were used for intracellular recording of membrane potentials from single smooth muscle cells. Electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence of guanethidine and atropine were recorded. Mediators of responses to nerve stimulation were also evaluated, using N-nitro-L-arginine methyl ester (L-NAME) and apamin.

Results—Mean resting membrane potential (RMP) was 41.5 ± 1.8 mV. Small membrane potential oscillations were observed in muscle cells. Single or multiple action potentials were often superimposed on the peaks of these oscillations. Spontaneous oscillations and action potentials were blocked by nifedipine. Transient hyperpolarizations of smooth muscle cell membrane potentials (inhibitory junction potentials [IJP]) were observed in response to electrical field stimulation. The IJP evoked by stimulus trains consisted of an initial fast component followed by a slow component. The L-NAME did not have a significant effect on RMP and did not significantly affect the fast component of IJP at any stimulus frequency tested. In contrast, L-NAME abolished the slow component of IJP observed after trains of pulses. In the continued presence of L-NAME, apamin had no significant effect on RMP but effectively reduced the fast component of IJP.

Conclusions and Clinical Relevance—Findings suggest that inhibitory neurotransmitters supplying equine jejunum act through different ionic mechanisms. Understanding these mechanisms may suggest new therapeutic targets for treatment of motility disorders. (Am J Vet Res 2000;61:362–368)

All Time Past Year Past 30 Days
Abstract Views 22 0 0
Full Text Views 262 142 48
PDF Downloads 52 26 3
Advertisement