Background: Nitric oxide (NO) may be an inhibitory neurotransmitter in the intestinal muscle. The present study examined its role in human and canine jejunum. Methods: Mechanical and intracellular electrical activity were recorded simultaneously from the circular muscle layer. Results: In the human jejunum, nerve stimulation inhibited mechanical activity and evoked an inhibitory junction potential that consisted of an initial fast hyperpolarization followed by a late sustained hyperpolarization. NO inhibited mechanical activity and evoked a dose-dependent hyperpolarization that mimicked the late hyperpolarization. In the canine jejunum, nerve stimulation inhibited mechanical activity and evoked an inhibitory junction potential that consisted of only a fast hyperpolarization. NG-Monomethyl-l-arginine and NG-nitro-l-arginine attenuated nerve-mediated inhibition of mechanical activity in both species. However, the effect of the synthase inhibitors on inhibitory junction potentials differed in the two species. In canine jejunum, both inhibitors reduced the amplitude of the initial fast hyperpolarization. In human jejunum, both inhibitors reduced only the late sustained hyperpolarization. Conclusuions: NO mediates neural inhibition in circular muscle of both human and canine jejunum through different mechanisms.
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