A comparison of the electrical properties and morphological characteristics of the smooth muscle of the rat and guinea-pig vas deferens

Microelectrodes were used to compare a variety of electrophysiological parameters of the rat and guinea-pig vas deferens. In comparison to the guinea pig, spontaneous junction potentials in the rat tissue were of shorter duration and occurred with greater frequency and amplitude. Action potentials induced by nerve stimulation could be observed in the smooth muscle of both species. However, in the rat tissue the majority of action potentials were generated in the impaled cell while 60% of the action potentials in the guinea-pig vas deferens were propagated. When current was intracellularly applied, spike potentials could be induced in approximately 90% of the cells of the rat vas deferens but in less than 10% of the cells of the guinea-pig vas deferens. The space constant was 1.48 mm for the guinea-pig vas deferens, but less than 0.5 mm for the rat vas deferens. Electromicroscopic examination of the homologous tissues indicates that the differences in electrical properties can be accounted for in part by differences in morphology. The incidence and intimacy of neuromuscular contacts was greater in the rat vas deferens while the incidence of nexuses between smooth muscle cells was greater in the guinea-pig tissue.