ROLE OF PROSTAGLANDIN-MEDIATED CYCLIC-AMP FORMATION IN PROTEIN-KINASE C-DEPENDENT SECRETION OF ATRIAL-NATRIURETIC-PEPTIDE IN RAT CARDIOMYOCYTES

The role of endogenous prostaglandin production in phorbol diester-induced myocardial atrial natriuretic peptide (ANP) secretion was investigated in cultured spontaneously beating ventricular rat cardiomyocytes. Incubation of cells with 4 beta-phorbol 12-myristate 13-acetate (PMA; 0.1 mu M) led to a rapid response in ANP release, a response accompanied by increases in cellular prostacyclin (PGI(2)) production, cyclic AMP (cAMP) formation and spontaneous contraction frequency. Although PMA-induced ANP secretion exhibited the pharmacological profile of a protein kinase C (PKC)-mediated event, the response was abolished in the presence of the cyclo-oxygenase inhibitors indomethacin (10 mu M) and diclofenac (1 mu M), indicating that endogenous prostaglandin production is responsible for PMA-induced ANP secretion in this system. Confirming this, PMA-induced ANP secretion was strongly correlated with endogenous formation of 6-oxo-prostaglandin F-1 alpha (r = 0.93, P < 0.0005, n = 11), and exogenously applied PGI(2), prostaglandin E(2) (PGE(2)) or prostaglandin F-2 alpha (PGF(2 alpha)) elicited simultaneous increases in cAMP formation, contraction frequency and ANP secretion in these cells. Furthermore, PMA-induced cAMP formation was abolished in the presence of either diclofenac or indomethacin, whereas the cAMP-elevating agent forskolin (0.1 mu M) mimicked the secretory and chronotropic effect of PMA in these cells. A role for cAMP in PMA-induced ANP secretion was also apparent insofar as PMA-induced ANP release was substantially decreased in the presence of the R(p)-diastereomer of 3',5'-cyclic adenosine monophosphorothioate (R(p)-cAMPS; 10 mu M), whereas the cAMP-mimetic agent dibutyryl cAMP(10 mu M) provoked a rapid increase in ANP secretion in this system. Finally, the Ca2+-channel antagonist nifedipine (0.1 mu M) severely decreased PGI(2)-, PGE(2)- and PMA-induced ANP secretion without affecting PGF(2 alpha)-induced peptide release, suggesting that PGI(2) and/or PGE(2), but not PGF(2 alpha), are the prostanoids involved in PMA induced ANP release. Taken together, these results suggest that PKC activation induces ANP secretion in spontaneously beating rat ventricular cardiomyocytes via an autocrine pathway involving increased PGI(2) and/or PGE(2) formation, a response leading to the activation of a myocardial adenylate cyclase and, subsequently, to that of a nifedipine-sensitive Ca2+ channel.