PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE CAUSES CA2+ RELEASE FROM RYANODINE CAFFEINE STORES THROUGH A NOVEL PATHWAY INDEPENDENT OF BOTH INOSITOL TRISPHOSPHATES AND CYCLIC-AMP IN BOVINE ADRENAL-MEDULLARY CELLS/

Pituitary adenylate cyclase-activating polypeptide (PACAP) causes both Ca2+ release and Ca2+ influx in bovine adrenal chromaffin cells, To e lucidate the mechanisms of PACAP-induced Ca2+ release, we investigated expression of PACAP receptors and measured inositol trisphosphates (I P3), cyclic AMP, and the intracellular Ca2+ concentration in bovine ad renal medullary cells maintained in primary culture, RT-PCR analysis r evealed that bovine adrenal medullary cells express the PACAP receptor hop, which is known to couple with both IP3 and cyclic AMP pathways. The two naturally occurring forms of PACAP, PACAP38 and PACAP27, both increased cyclic AMP and IP3, and PACAP38 was more potent than PACAP27 in both effects. Despite the effects of PACAP on IP3 production, the Ca2+ release induced by PACAP38 or by PACAP27 was unaffected by cinnar izine, a blocker of IP3 channels. The potencies of the peptides to cau se Ca2+ release in the presence of cinnarizine were similar, The Ca2release induced by PACAP38 or by PACAP27 was strongly inhibited by rya nodine and caffeine, In the presence of ryanodine and caffeine, PACAP3 8 was move potent than PACAP27, PACAP-induced Ca2+-release was unaffec ted by Rp-adenosine 3',5'-cyclic monophosphothioate, an inhibitor of p rotein kinase A. Ca2+ release induced by bradykinin and angiotensin II was also inhibited by ryanodine and caffeine, but unaffected by cinna rizine. Although IP3 production stimulated by PACAP38 or bradykinin wa s abolished by the phospholipase C inhibitor, U-73122, Ca2+ release in response to the peptides was unaffected by U-73122, These results sug gest that PACAP induces Ca2+ release from ryanodine/caffeine stores th rough a novel intracellular mechanism independent of both IP3 and cycl ic AMP and that tile mechanism may be the common pathway through which peptides release Ca2+ in adrenal chromaffin cells.