CA2+ CHANNEL ANTAGONISTS AND INHIBITION OF PROTEIN-KINASE-C EACH BLOCK CONTRACTION BUT NOT DEPOLARIZATION TO 5-HYDROXYTRYPTAMINE IN THE RABBIT BASILAR ARTERY

The Ca2+ channel antagonists nifedipine and verapamil each significantly inhibited (50-100%) the smooth muscle contraction induced in response to either 5-hydroxytryptamine (1 muM, 5-HT) or 20 mM K+ (K+-physiological salt solution) in the basilar artery. Simultaneous measurements of smooth muscle membrane potential showed that changes in potential were not modified at this time. A similar inhibitory action against the smooth muscle contraction but not the depolarization to 5-HT was obtained with the putative protein kinase C and phospholipase C inhibitors, 1-(5-isoquinolinesulphonyl)-2-methylpiperazine (10 muM, H7) and 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (70 muM, NCDC). These data indicate that 5-HT-induced Ca2+ influx through voltage sensitive channels is important for smooth muscle contraction but not depolarization in the rabbit basilar artery.