Intracellularly recorded electrical activity of smooth muscle of guinea pig oviduct

Action potentials of the simple spike form, similar to those observed in the longitudinal myometrium, were recorded intracellularly from the strands of longitudinal muscle that are associated with the guinea pig oviduct. Action potentials recorded from the circular layer were dominated by a prolonged (1- to 10-s) plateau component that was sometimes preceded by a spike. Electrotonic potentials in response to hyperpolarizing current pulses are consistent with the view that the plateau component might be associated with an increase in membrane conductance. Action potentials of circular smooth muscle were resistant to changes in the extracellular cationic concentration. Increasing external Ca2+ prolonged the duration of the plateau component of the action potential in the region nearest the uterus on days 3 and 4 after ovulation: Ca2+ had no consistent effect at other times during the estrous cycle or on ampullary segments at any time. Reducing the concentration of external Cl- in the presence of Na+ resulted in a significant increase in the amplitude of the plateau.