The passive membrane properties and excitatory junction potentials of the guinea pig deferens.

Abstract

Electrotonic potentials were recorded from the superficial smooth muscle cells of the guinea-pig vas deferens, in response to low-amplitude, long-duration (.gtoreq. 2 s) pulses. Averaging techniques were used to increase the signal/noise ratio and the intracellularly recorded electrotonic potentials were corrected for extracellular voltage drop across the bath series resistance. Since the length of tissue in the stimulating and recording compartments affects the time course of electrotonic potentials the passive membrane properties were measured with known amounts of tissue in these 2 compartments. The length constant (.lambda.) was 0.86 mm and the membrane time constant (.tau.m) was 270 msec. Excitatory junction potentials (e.j.p.s) were recorded and averaged in response to field stimulation of intact branches of the hypogastric nerve. The mean time constant of the exponential decay phase of the e.j.p. (288 ms) was similar to the (.tau.m = 270 ms). As the e.j.p. showed little change in amplitude or time constant of decay when recorded up to several millimeters from the stimulating electrode it was assumed that the tissue was isopotential during the e.j.p., and an estimate was made of the time course of the underlying junctional current. The estimated time course of the junctional current during an e.j.p. was similar to the observed time course of a spontaneous junction potential (s.e.j.p.). As the time course of the junctional current during an s.e.j.p. is similar to the time course of the potential change, the factors which determine the time course of the current underlying the s.e.j.p. apparently also determine the time course of the e.j.p. current.