Selective inhibition of cyclic AMP and cyclic GMP phosphodiesterases of cardiac nuclear fraction.

Approximately 60% of the total particulate phosphodiesterase activity occurring in cardiac tissue was associated with the nuclear fraction. Cyclic GMP phosphodiesterase activity of the purified cardiac nuclear fraction was selectively inhibited by trifluoperazine (I50 = 19 microM) with negligible inhibition (less than 15%) of cyclic AMP phosphodiesterase activity. Inhibition of cyclic GMP phosphodiesterase by trifluoperazine was calcium-dependent and suppressed by ethylene glycol bis (beta-aminoethyl ether)N, N, N', N'-tetraacetic acid (EGTA). The inhibitory response of both phosphodiesterases to papaverine was similar in the presence of calcium. However, in the presence of EGTA, papaverine inhibition of cyclic GMP but not cyclic AMP phosphodiesterase was reduced significantly. Calmodulin (1-5 micrograms/ml) readily reversed the inhibition by 25 microM trifluoperazine of membraneous cyclic GMP phosphodiesterase, but had no effect on inhibition by papaverine. With imidazolidinone analogues (Ro 7-2956 and Ro 20-1724), EGTA enhanced the inhibition of cyclic GMP phosphodiesterase without significantly altering the inhibition of cyclic AMP phosphodiesterase. Inhibition of cyclic AMP of cyclic GMP phosphodiesterase activity by 1-methyl-3-isobutylxanthine, quinidine, or compound SQ 20,009 was not affected appreciably by calcium or EGTA. The selective inhibitory action of certain pharmacological agents on phosphodiesterases of cardiac nuclear fraction and the modulation of the inhibitory response by calcium suggest an intrinsic and predominant association of calmodulin with cyclic GMP phosphodiesterase activity of these membranes.