SPECIFIC ACTIVATION OF ADENYLYL-CYCLASE-V BY A PURINERGIC AGONIST

The present study was designed to investigate whether and how the puri nergic stimulation of rat ventricular myocytes modulates the cAMP-depe ndent pathway. Stimulation of cardiomyocytes with ATP gamma S in the p resence of the phosphodiesterase inhibitor IBMX increases by 3-fold in tracellular cAMP content. In contrast to beta-adrenergic stimulation, the purinergic stimulation of adenylyl cyclase was not inhibited by ac tivation or enhanced by inhibition of a G(i) protein. Forskolin did no t potentiate the effect of extracellular ATP gamma S on intracellular cAMP content but the effect of isoproterenol did, Like isoproterenol, the purinergic agonist decreased subsequent ADP-ribosylation of a 45 k Da G(alpha s) by cholera toxin, ATP gamma S also increased cAMP conten t in neonatal rat cardiomyocytes, a cell type that expresses a long fo rm of G(s) protein (alpha(s), 52 kDa) in contrast to adult rat cardiom yocytes that express mostly a short form of G(s) protein (alpha(s), 45 kDa), Both purinergic and beta-adrenergic agonists increased cAMP in HEK 293 cells expressing type V adenylyl cyclase while cAMP was only i ncreased by beta-adrenergic stimulation of HEK expressing type IV or V I adenylyl cyclases, Thus, we propose that the purinergic and beta-adr energic stimulations differentially activate adenylyl cyclase isoforms in rat cardiomyocytes and that adenylyl cyclase V is the specific tar get of the purinergic stimulation. (C) 1998 Federation of European Bio chemical Societies.