POSSIBLE ROLE OF NITRIC-OXIDE IN CATECHOLAMINE SECRETION BY CHROMAFFIN CELLS IN THE PRESENCE AND ABSENCE OF CULTURED ENDOTHELIAL-CELLS

We studied the effect of cultured endothelial cells on the secretion o f catecholamines by cultured bovine chromaffin cells. Chromaffin cell catecholamine secretion was stimulated by either boluses of potassium (K+) or the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) . Endothelial cells inhibited the catecholamine release and stimulator y effects of K+ and DMPP. This inhibition increased with time, and in 25 min the initial stimulated secretory response (100%) to 30 mM K+ or 25 mu M DMPP dropped to 45 +/- 3% and 53.5 +/- 2.3%, respectively. Th is endothelial cell-induced inhibition was blocked by the nitric oxide synthase inhibitors N-nitro-L-arginine methyl ester (L-NAME) and N-mo noethyl-L-arginine (L-NMMA), and by the guanylate cyclase inhibitor me thylene blue, indicating that the L-arginine/nitric oxide/ cyclic GMP pathway is involved in this endothelial cell-chromaffin cell interacti on. In the absence of endothelial cells, incubation of chromaffin cell s with L-NAME, LNMMA, or methylene blue also augmented the secretagogu e-induced catecholamine secretion, indicating that nitric oxide from c hromaffin cells could be implicated in an autoinhibitory process of ca techolamine release. These results provide indirect evidence for the p resence of nitric oxide synthase in bovine adrenomedullary chromaffin cells. Our results show that there is an autoinhibitory mechanism of c atecholamine release in chromaffin cells and that an additional level of inhibition is observed when cultured vascular endothelial cells are present. These two inhibitory processes may have different origins, b ut they appear to converge into a common pathway, the L-arginine/nitri c oxide synthase/guanylate cyclase pathway.