Two neuropeptides, enkephalin and vasoactive intestinal polypeptide (VIP), are simultaneously increased in cultures of bovine chromaffin cells after diverse treatments including elevation of cAMP, application of nicotine, or chronic depolarization. We now show that phorbol esters can specifically elevate VIP in cultured chromaffin cells without changing the amount of enkephalin. Peptide histidine isoleucine, a VlP-related peptide, is also expressed concomitantly with VIP after treatment with phorbol ester. Immunocytochemical examination of drug-treated cells defines a subpopulation of chromaffin cells which are responsive to phorbol ester stimulation. The unique ability of phorbol esters to selectively regulate VIP expression indicates the presence of independent mechanisms for controlling the expression of individual neuropeptides in chromaffin cells.
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