Modulation of stimulus-secretion coupling in porcine adrenal chromaffin cells by receptor-mediated increases in protein kinase C activity

Catecholamine (CAT) secretion by adrenal chromaffin cells is primarily trig gered by nicotinic receptor-dependent increases in cytosolic Ca2+. The prin cipal aim of the present study was to determine whether pituitary adenylate cyclase activating peptide (PACAP), which is coreleased with acetylcholine from the splanchnic nerve, can modulate nicotinic receptor-dependent Ca2signaling and catecholamine secretion in porcine adrenal medullary chromaff in (PAMC) cells. Activation of protein kinase C (PKC) with phorbol myristat e acetate (PMA) dose- and time-dependently inhibited nicotine (NIC)-induced Ca2+ transients. At 100 nM PMA, peak Ca2+ levels were reduced by 27% +/- 2 % (P < 0.05) and 41% +/- 3% (P < 0.05) after 10 and 20 min exposure, respec tively. The inhibitory effects of PMA were significantly reduced by preincu bation with the PKC inhibitor staurosporine. KCI-induced Ca2+ transients we re also reduced by 20 min PMA treatment (Delta -27% +/- 4%; P < 0.05), sugg esting that PKC affects voltage-gated Ca2+ channel activity. Pretreatment w ith PACAP also resulted in both time- and concentration-dependent suppressi on of Ca2+ transients. After 20 min exposure to 1 mu M PACAP, NIC- and KCI- induced transients were reduced by 36% +/- 5% (P < 0.05) and 51% +/- 6% (P < 0.05), respectively. These effects could also be prevented by staurospori ne pretreatment. NIC-induced CAT secretion was significantly reduced by pre treatment with both PMA (Delta -56% +/- 2%; P < 0.05) and PACAP (Delta-53% +/- 7%; P < 0.05). This suppressive effect on secretion could be prevented by pretreatment with staurosporine. These data suggest that, in addition to having direct stimulatory effects on catecholamine synthesis and secretion , PACAP can also negatively modulate nicotinic receptor-dependent Ca2+ sign aling and secretion in PAMC cells. J. Neurosci. Res. 59:760-766, 2000. (C) 2000 Wiley-Liss, Inc.