Cyclic GMP-Mediated Phospholamban Phosphorylation in Intact Cardiomyocytes

The cGMP-mediated phospholamban phosphorylation was investigated in cardiomyocytes in response to receptor-dependent (atrial natriuretic peptide, ANP) and -independent (sodium nitroprusside; SNP) cGMP generation. ANP (InM-1μM) induced phospholamban phosphorylation in a concentration-dependent fashion (EC 50: 5.0±0.09 nM). Concomitantly, an elevation in cGMP levels was observed. Phospholamban was also dose-dependently phosphorylated in response to SNP, but it required about three orders of magnitude higher concentrations (EC 50: 2.9±0.03 μM) than ANP. Treatment of the cells with 8Br-cGMP (10 μM) or with the specific activator of cGMP-protein kinase 8-pCPT-cGMP (1-100 μM) mimicked these effects. The results demonstrate for the first time that a ANP/cGMP signaling pathway exists in neonatal cardiomyocytes which may contribute to modulation of heart contractility.