Transmembrane voltage of opossum esophageal smooth muscle and its response to electrical stimulation of intrinsic nerves

Abstract

This study was designed to examine the transmembrane potential of esophageal circular smooth muscle both before and in response to electrical stimulation of the intrinsic neural plexus, and to determine if regional differences are present in these potentials. Transverse strips of the opossum esophagus were prepared from sites located 1,3,5, and 7 cm above the gastroesophageal junction and subjected to 1-s trains of square-wave pulses. The effects of varying pulse frequency, voltage, and duration were assessed by conventional microelectrode techniques. The latency of the electrical off response ranged from a mean value of 1.08 s at 5 Hz to 1.0 s at 16 Hz when measured in cells from strips 5 cm above the gastroesophageal junction. Associated with this increase in latency is both an increase in the mean amplitude of hyperpolarization and a fall in the rate of the ensuing depolarization. In contrast, an increase in pulse voltage or duration had no effect on electrical off response latency. Resting potential analyzed on a regional basis ranged from a mean of −52.8 mV to −43.5 mV in strips 7 cm and 1 cm above the gastroesophageal junction respectively. Electrical off response latencies also demonstrated regional differences ranging from 1.06 to 1.50 s in strips taken 7 cm and 3 cm above the gastroesophageal junction respectively. Associated with the prolonged latencies noted in the more aboral strips was a decrease in the average rates of both membrane hyperpolarization and ensuing depolarization. It can be concluded from these studies that (a) within a given region an increase in stimulus frequency increases the mean amplitude of hyperpolarization, decreases the rate of the ensuing depolarization, and prolongs the electrical off response latency; (b) mean resting potential of esophageal circular smooth muscle cell becomes gradually less negative in an oral to aboral direction; and (c) cells of the more aboral smooth muscle segments studied demonstrated a decrease in the average rates of both membrane hyperpolarization and ensuing depolarization, and a prolonged electrical off response latency.