Neuropeptide Y (18-36) modulates chromaffin cell catecholamine secretion by blocking the nicotinic receptor ion...

Neuropeptide Y (NPY) is a widely distributed peptide with varied activities including inhibition of [3H]NE secretion from chromaffin cells. In the present study, we investigated the mechanism through which NPY and NPY fragments inhibit nicotinic receptor induced influx of 22Na+ and 45Ca++ into bovine chromaffin cells. Fragments of NPY, including NPY13-36, NPY18-36 and NPY26-36, are more potent inhibitors of 45Ca++ and 22Na+ influx than NPY. High [K+]- and BAY K 8644-induced 45Ca++ influx and veratridine-induced 22Na+ influx are not inhibited by either NPY or NPY fragments. Thus, the site of NPY or NPY fragment action is not voltage-gated Ca++ or Na+ channels. A significant amount of acetylcholine-induced 45Ca++ influx still occurs in the presence of the voltage-gated Ca++ channel blockers: nifedipine (L-type), omega-conotoxin-GVIA (N-type) and omega-agatoxin-IVA (P-type). NPY18-36, in the presence of these channel blockers, inhibited the residual nicotinic receptor-induced Ca++ influx. The response to NPY 18-36 is not pertussis toxin sensitive. The rank orders of potency for inhibition of 45Ca++ and 22Na+ are the same: NPY18-36 > or = NPY26-36 > NPY13-36 > NPY13-36 > NPY > or = NPYfree acid. Moreover, the IC50 values for NPY18-36 inhibition of 45Ca++ influx and 22Na+ influx are similar, 0.9 x 10(-6) M and 2.03 x 10(-6) M, respectively. Regression analysis for inhibition of these two phenomena produced a correlation coefficient of .9697 (P < .0003).(ABSTRACT TRUNCATED AT 250 WORDS)