[Nifedipine inhibits calcium-dependent potentials in guinea pig sympathetic neurons]

Reversible effects of nifedipine, a calcium channel blocker, on 3 types of calcium-dependent potentials in the celiac ganglion cells of the guinea pigs in vitro were investigated by means of intracellular recordings. Nifedipine (0.1-1 mmol/L) inhibited the spike afterhyperpolarization, the post-tetanic membrane potential in dose-dependent manner. Nifedipine (0.1 mumol/L) also depressed the Ca2+ spike potential in a Na(+)-free/high Ca2+ solution plus TEA. Thus the results indicate that nifedipine in clinical therapeutic dosage may directly reduce Ca2+ conductance and then in higher concentration may also depress secondarily Ca(2+)-dependent potassium conductance. These actions of nifedipine may underlie the mechanism of blockade of quantal release of ACh from presynaptic membrane as well as the modulation of excitability of sympathetic postganglionic neuron.