SARCOPLASMIC RETICULUM-ASSOCIATED CYCLIC ADENOSINE 5'-MONOPHOSPHATE PHOSPHODIESTERASE ACTIVITY IN NORMAL AND FAILING HUMAN HEARTS

Sarcoplasmic reticulum-associated cAMP phosphodiesterase activity was examined in microsomes prepared from the left ventricular myocardium of eight heart transplant recipients with end-stage idiopathic dilated cardiomyopathy and six unmatched organ donors with normal cardiac function. At cAMP concentrations less-than-or-equal-to 1.0-mu-M, sarcoplasmic reticulum-associated cAMP phosphodiesterase activity was functionally homogeneous. cAMP phosphodiesterase activity was inhibited competitively by cGMP (K(i) = 0.031 +/- 0.008-mu-M) and the cilostamide derivative OPC 3911 (K(i) = 0.018 +/- 0.004-mu-M), but was essentially insensitive to rolipram. V(max) and K(m) were 781.7 +/- 109.2 nmol/mg per min and 0.188 +/- 0.031-mu-M, respectively, in microsomes prepared from nonfailing hearts and 793.9 +/- 68.9 nmol/mg per min and 0.150 +/- 0.027-mu-M in microsomes prepared from failing hearts. Microsomes prepared from nonfailing and failing hearts did not differ with respect to either the ratio of cAMP phosphodiesterase activity to ATP-dependent Ca2+ accumulation activity or the sensitivity of cAMP phosphodiesterase activity to inhibition by OPC 3911. These data suggest that the diminished inotropic efficacy of phosphodiesterase inhibitors in failing human hearts does not result from changes in the level, kinetic properties, or pharmacologic sensitivity of sarcoplasmic reticulum-associated cAMP phosphodiesterase activity.