The effects of Bay K 8644 and nifedipine on the electrical and mechanical responses of the distal ear artery of the rabbit to stimulation of the perivascular nerves were studied. Neural stimulation elicited excitatory junction potentials (e.j.ps) in the smooth muscle cells of the artery. An action potential was generated when the e.j.p. reached a threshold of about -53 mV. Contraction was always triggered by the action potential. Bay K 8644 at low concentrations (7 X 10(-8) M) had no significant effect on the resting membrane potential and the e.j.p. However the amplitudes of the action potential, and the contraction were potentiated by Bay K 8644. Multiple action potentials could also be generated from a single e.j.p. At higher concentrations, Bay K 8644 (3 X 10(-6) M) caused membrane depolarization, development of vascular tone and spontaneous action potentials. All the effects of Bay K 8644 could be reversed by exposure to light. Nifedipine (3 X 10(-7) M) inhibited the action potential and the resulting contraction. The effect of nifedipine could be reversed by Bay K 8644 but not by light. These results demonstrate that the excitatory and inhibitory effects of Bay K 8644 and nifedipine on vascular smooth muscle are associated with changes in the electrical responses.