Characterization and mediation of inhibitory junction potentials from opossum lower esophageal sphincter

Background: Activating nonadrenergic, noncholinergic (NANC) nerves of the lower esophageal sphincter (LES) hyperpolarizes and relaxes its circular smooth muscle. This relaxation is mediated by nitric oxide (NO) or an NO-containing compound. These studies were undertaken to compare the electrophysioiogical responses of circular smooth muscle from the LES and esophagus in response to NANC nerve stimulation and to test the hypothesis that NO mediates LES hyperpolarization. Methods: The transmembrane potential difference was recorded with glass microelectrodes. Nerve-mediated membrane responses were evoked by electrical pulses of 0.5 msec duration and 50 V amplitude. Results: Responses of LES muscle differed from those of the esophageal muscle. The duration of hyperpolarization was much longer in sphincteric muscle. The depolarization that followed hyperpolarization of esophageal muscle was not observed in sphincteric muscle. N^G-nitro-l-arginine, an inhibitor of NO synthase, attenuated the nerve-induced hyperpolarization. l-arginine, the substrate for NO synthase, antagonized the effect of N^G-nitro-l-arginine. Exogenous NO hyperpolarized of the smooth muscle membrane. Conclusions: These data support the hypothesis that NO or an NO-like compound may mediate nerve-induced hyperpolarization of the opossum LES.