AJP - Gastrointestinal and Liver Physiology, Vol 261, Issue 5 752-G762, Copyright © 1991 by American Physiological Society

ARTICLES

Chloride-mediated inhibitory junction potentials in opossum esophageal circular smooth muscle

J. R. Crist, X. D. He and R. K. Goyal
Center for Swallowing and Motility Disorders, Charles A. Dana Research Institute, Beth Israel Hospital, Boston, Massachusetts.

Intracellular recordings were made from circular smooth muscle cells of the opossum esophagus. Inhibitory junction potentials (IJPs) 8.3 +/- 0.7 mV in amplitude were observed in response to a single pulse (1 ms, 15 mA) of transmural nerve stimulation. Potassium channel blockers apamin (1 microM), tetraethylammonium (10 mM), 4-aminopyridine (250 microM), and cesium chloride (10 mM) did not reduce IJP amplitude. Conditioning hyperpolarizations to the equilibrium potential for potassium were associated with a significant increase in IJP amplitude. A small increase in membrane resistance was observed during the IJP. Changes in external potassium concentration had no significant effect on IJP amplitude acutely. However, prolonged perfusion with potassium-free Krebs solution resulted in a marked decrease in IJP amplitude as did prolonged perfusion with ouabain (0.1 mM). Low-chloride solution (12.4 mM) resulted acutely in an increase in IJP amplitude. Prolonged low-chloride perfusion resulted in a significant decrease in IJP amplitude. The anion exchange chloride channel inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (600 microM) significantly reduced IJP amplitude. These findings suggest that the IJP observed in opossum esophageal circular smooth muscle in response to a single pulse of stimulation is due to a decrease in membrane chloride conductance. The ability of prolonged application of Na-K pump inhibitors to abolish the IJP appears to be due to known secondary effects of these agents in depleting intracellular chloride.

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