Electrical activity of the smooth muscle of guinea-pig oviduct and effects of catecholamines.

The membrane activity of the oviductal smooth muscle cell of the nonpregnant guinea pig was studied intracellularly. The membrane potential was about 50 mV. The cells used were spontaneously active in normal solution. Spontaneous action potentials were recorded from the regions of infundibulum, isthmus, and ampulla of the oviduct. Action potentials were composed of repetitive spikes and a plateau phase and the duration of the plateau phase ranged from 2 sec to 6 sec. The amplitude of the plateau phase was about 20 mV. The shape of the spontaneous action potential obtained from the mesosalpinx differed from that of the oviduct. Adrenaline, noradrenaline, and phenylephrine evoked the excitatory action. In general, small depolarization, increase in spikes on a plateau, and prolongation of the plateau duration occurred because of these drugs. After the treatment with phentolamine, adrenaline inhibited spike generation. Isoprenaline decreased the number of spikes on the plateau and the plateau duration. At higher concentration of isoprenaline, the membrane activity was abolished. The inhibitory effect of isoprenaline was blocked by propranolol. Prostaglandin F2-alpha excited membrane activity. These results indicate that the sympathetic innervation of the oviductal smooth muscle is alpha-excitatory and beta-inhibitory.