Phorbol esters and cyclic AMP activate AMP deaminase in adult rat cardiac myocytes.
Using rapid deenergization as a probe for adenylate deaminase activity in intact adult rat cardiac myocytes, we have previously established that IMP formation is enhanced by alpha-adrenergic agonists. In the present study, the effect of adrenergic agents on adenylate deaminase was further characterized. Phenylephrine (PE)3 increased IMP production in a dose-dependent fashion with an EC50 of 8 x 10(-7) M. The response to PE was reversed within 10 min by the alpha 1-antagonist, prazosin. Likewise, adenylate deaminase was also activated in ventricular myocytes challenged with phorbol 12-myristate 13-acetate (PMA, EC50 = 5 nM); cardiac cells presented with 100 nM PMA increased IMP production from 4.4 +/- 0.5 (control) to 15.7 +/- 0.9 nmol/mg protein when subsequently deenergized. The effects of PMA and PE were attenuated 85 +/- 5% and 96 +/- 4%, respectively, by pretreatment of cells with 150 nM staurosporine, an inhibitor of protein kinase C. Furthermore, incubation of cardiac cells with 1 microM PMA for 24 h blunted the response to both PMA and phenylephrine 85-90%. Elevating cyclic AMP (cAMP) content to greater than 15 pmol/mg by treatment with forskolin or isoproterenol plus isobutylmethylxanthine also resulted in enhanced adenylate deaminase activity, but this stimulatory effect was not abolished by 24 h incubation with 5 microM PMA. Forskolin and PMA-induced increases in IMP production appeared to be additive. However, 0.5 microM isoproterenol inhibited the cellular response to phenylephrine by about 30% but did not affect PMA-stimulated adenylate deaminase activity. We conclude that both cAMP and protein kinase C stimulate adenylate deaminase, perhaps through selective activation of different isoforms. However, cAMP also exerts partial inhibition on alpha-adrenoreceptor-mediated increases in IMP production.
Department of Medical Biochemistry, Ohio State University, Columbus 43210.
B
B
Hu
R A
RA
Altschuld
C M
CM
Hohl
D000659:AMP Deaminase / Q000378:metabolism*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation; D004837:Epinephrine / Q000494:pharmacology; D007291:Inosine Monophosphate / Q000378:metabolism; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D010656:Phenylephrine / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D000470:Alkaloids; D007291:Inosine Monophosphate; D010656:Phenylephrine; D000242:Cyclic AMP; D011493:Protein Kinase C; D000659:AMP Deaminase; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate; D004837:Epinephrine