The effects of Bay K 8644 and nifedipine on the neural responses of the rabbit ear artery

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Abstract
1 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. 2 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. 3 Bay K 8644 at low concentrations (7 × 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. 4 At higher concentrations, Bay K 8644 (3 × 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. 5 Nifedipine (3 × 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. 6 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.