ROLE OF CAMP AND CALCIUM INFLUX IN ENDOTHELIN-1-INDUCED ANP RELEASE IN RAT CARDIOMYOCYTES

The mechanism of endothelin-1 (ET-1)-induced atrial natriuretic peptid e (ANP) release was studied in neonatal rat ventricular cardiomyocytes . These cells expressed a single high-affinity class of ETA receptor ( dissociation constant = 54 +/- 18 pM, n = 3), but no ETB receptors. In cubation of cardiomyocytes with ET-1 led to concentration-dependent AN P release and prostacyclin production. ET-1-induced ANP release was af fected by neither protein kinase C (PKC) inhibition or downregulation nor by cyclooxygenase inhibition, indicating that ET-1-stimulated ANP secretion is not a PKC-mediated, prostaglandin-dependent process. Furt hermore, ET-1 significantly stimulated adenosine 3',5'-cyclic monophos phate (cAMP) production and increased cytosolic calcium concentration in these preparations. Both ET-1-induced calcium influx and ANP releas e were decreased by the cAMP antagonist Rp-cAMPS, the Rp diastereoisom er of cAMP. Moreover, ET-1-induced ANP secretion was strongly inhibite d in the presence of nifedipine as well as in the absence of extracell ular calcium. Thus our results suggest that ET-1 stimulates ANP releas e in ventricular cardiomyocytes via an ETA receptor-mediated pathway i nvolving cAMP formation and activation of a nifedipine-sensitive calci um channel.