Intracellular microelectrode recording to characterize inhibitory neuromuscular transmission in jejunum of horses.
OBJECTIVE
To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons.


METHODS
Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease.


METHODS
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
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.
Rakestraw
P C
PC
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis 95616, USA.
Snyder
J R
JR
Sanders
K M
KM
Shuttleworth
W C
WC
D000818:Animals; D001030:Apamin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006736:Horses / Q000502:physiology*; D007583:Jejunum / Q000187:drug effects / Q000294:innervation*; D008839:Microelectrodes; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*
D004791:Enzyme Inhibitors; D001030:Apamin; D019331:NG-Nitroarginine Methyl Ester