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

This research article investigates the electrical activity of horse’s jejunal circular muscle, and how it responds to stimulation by intrinsic inhibitory neurons. The findings suggest that inhibitory neurotransmitters work through different ionic mechanisms in horse’s jejunal muscle, and therefore could offer new treatment options for motility disorders.

Objective and Methodology

• The primary objective of the study was to understand the electrical responses of jejunal circular muscle in horses when stimulated by intrinsic inhibitory neurons. For this purpose, the researchers procured jejunum samples from horses that were euthanized for reasons not related to gastrointestinal disease.
• Isolated circular muscle preparations were kept oxygenated using a modified Krebs solution. For recording intracellular membrane potentials from individual smooth muscle cells, the researchers used glass microelectrodes.
• They recorded the electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence of two chemical compounds named guanethidine and atropine.
• Lastly, the researchers also evaluated mediators of responses to nerve stimulation using N-nitro-L-arginine methyl ester (L-NAME) and apamin.

Findings

• The study observed small membrane potential oscillations in muscle cells and recorded the mean resting membrane potential (RMP) as 41.5+/-1.8 mV. Frequently, single or multiple action potentials were seen on the peaks of these oscillations.
• The researchers discovered these spontaneous oscillations and action potentials could be blocked by using nifedipine, a calcium channel blocker.
• In response to electrical field stimulation, brief hyperpolarizations of smooth muscle cell membrane potentials or inhibitory junction potentials (IJP) were observed. The IJP evoked by stimulus trains consisted of a quick component followed by a slow one.
• The study found that while L-NAME did not significantly affect the RMP or the fast component of IJP, it obliterated the slow component of IJP observed after trains of pulses.
• When L-NAME was continuously present, apamin did not have a significant effect on the RMP, but reduced the fast component of IJP effectively.

Implications of the Study

• The findings indicate that the inhibitory neurotransmitters supplying horse’s jejunum function through different ionic mechanisms.
• This understanding could offer fresh insights into how the motility disorders in horses could be potentially treated by targeting these mechanisms.