Properties of excitatory junction potentials and currents in smooth muscle cells of the mouse vas deferens.

Intracellular recordings made from superficial smooth muscle cells of the mouse vas deferens confirmed the presence of two populations of cells, distinguishable by their membrane potential and measured input resistance. In this study, we have concentrated on cells with high input resistance (50-500 M omega) and membrane potentials of -45 to -65 mV. These cells fired action potentials when depolarized by intracellular current injection and appeared to be electrically isolated from adjacent cells. Stimulation of the intramural nerves evoked excitatory junction potentials (e.j.p.s.), which fluctuated in amplitude, with the largest firing action potentials. The e.j.p. amplitude was increased by hyperpolarizing and decreased by depolarizing the cell membrane. Under voltage-clamp, nerve stimulation evoked excitatory junction currents (e.j.c.s.) which reached a peak in 5 ms, and declined exponentially with a time-constant of 28 ms. The e.j.c. amplitude was linearly related to membrane potential with a reversal potential near -10 mV.