ELECTROPHYSIOLOGICAL COMPARISON OF THE ACTION OF OXYTOCIN AND CARBACHOL ON PREGNANT MOUSE MYOMETRIUM

Abstract

Effects of oxytocin and carbachol on the membrane potential, membrane conductance, and spike potential of pregnant mouse myometrium were investigated in isotonic and hypertonic solutions.1) In an isotonic solution low concentrations of oxytocin (10-6-10-5 U/ml) did not cause any change in the membrane potential or in the amplitude of the action potential, but facilitated the conduction of excitation. With these concentrations, spontaneous contractions of truncated pattern became full-size.2) Intermediate concentrations of oxytocin (10-4 U/ml) and carbachol (10-5 g/ml) caused a depolarization and an acceleration of spike activity. Higher concentration of oxytocin or carbachol caused a peak depolarization to about -25 mV. During the recovery in normal solution, membranes showed oscillatory slow waves.3) Depolarization and cessation of spike activity by 10-3 U/ml oxytocin were maintained. The membrane tended to repolarize and resumed the spike activity in 10-20 min in the continuous presence of 10-4 g/ml carbachol in isotonic solution.4) In hypertonic solution the depolarization produced by these drugs was smaller, e.g., 10-3 U/ml oxytocin or 10-4 g/ml carbachol depolarized the membrane to -40--30 mV. When the membrane was depolarized by the drugs, membrane conductance was increased.