Intracellular studies of electrical membrane properties of opossum esophageal circular smooth muscle.

It has been suggested that regional differences in membrane properties of circular esophageal smooth muscle play an important role in the mechanism of esophageal peristalsis. The purpose of this study was to examine both the passive and active membrane properties of circular smooth muscle at proximal and distal esophageal sites so as to delineate the role of myogenic properties in the intramural mechanism of peristalsis. Intracellular recordings were made in circular muscle strips taken from proximal (8 cm above the gastroesophageal junction) and distal (2 cm above the gastroesophageal junction) sites in 10 opossums using the partition method of Abe and Tomita. At both esophageal sites, determinations were made of resting membrane potentials, time constants, space constants, thresholds for action potentials, action potential amplitudes, rates of rise of action potentials, and action potential durations at half-amplitude. The values for these parameters at the proximal and distal sites, respectively, were as follows: mean resting membrane potential, 49.7 +/- 0.24 and 49.5 +/- 0.3 mV; length constant, 4.0 +/- 0.4 and 3.8 +/- 0.4 mm; time constant, 513 +/- 49 and 456 +/- 53 ms; threshold for action potentials, 9.3 +/- 0.4 and 8.8 +/- 0.3 mV; amplitude of action potentials, 36.0 +/- 5.2 and 35.3 +/- 1.7 mV; rate of rise of action potentials, 2.3 +/- 0.3 and 2.6 +/- 0.4 mV/ms; duration of action potentials at half-amplitude, 5.0 +/- 1.2 and 4.1 +/- 0.4 ms; and the conduction velocity for evoked potentials, 3.9 +/- 0.3 and 3.8 +/- 0.4 cm/s. Our studies show that there are no differences between proximal and distal esophageal sites in any of these determinations. These studies also show that regional differences in the electrical membrane properties of circular smooth muscle do not account for esophageal peristalsis.