Chloride-mediated inhibitory junction potentials in opossum esophageal circular smooth muscle.
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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Center for Swallowing and Motility Disorders, Charles A. Dana Research Institute, Beth Israel Hospital, Boston, Massachusetts.
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Goyal
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D000818:Animals; D018118:Chloride Channels; D002712:Chlorides / Q000502:physiology*; D004594:Electrophysiology; D004947:Esophagus / Q000502:physiology*; D005260:Female; D007477:Ions; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008839:Microelectrodes; D009130:Muscle, Smooth / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D009893:Opossums; D010042:Ouabain / Q000494:pharmacology; D010539:Permeability; D015221:Potassium Channels / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology
D018118:Chloride Channels; D002712:Chlorides; D007477:Ions; D008565:Membrane Proteins; D015221:Potassium Channels; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase