ERYTHRO-9-(2-HYDROXY-3-NONYL)ADENINE INHIBITS CYCLIC GMP-STIMULATED PHOSPHODIESTERASE IN ISOLATED CARDIAC MYOCYTES

Recently, an inhibitor of adenosine deaminase, erythro-9-(2-hydroxyl-3 -nonyladenine (EHNA), was shown to selectively block the activity of p urified cGMP-stimulated phosphodiesterase (PDE) (cGS-PDE, or PDE2) in human and porcine heart [J. Mol. Cell. Cardiol. 24 (Suppl. V):102 (199 2)]. Because cGS-PDE was found to mediate the cGMP-induced inhibition of L-type Ca2+ current (I-Ca) in frog ventricular cells, we tested the effects of EHNA in this preparation. I-Ca was measured using the whol e-cell patch-clamp technique and a perfusing pipette. EHNA (0.3-30 mu M) had no significant effect on either basal I-Ca or isoprenaline (1 n M)- or cAMP (10 mu M)-elevated I-Ca. However, EHNA dose-dependently (I -Ca approximate to 3 mu M) reversed the inhibitory effect of cGMP on c AMP-stimulated I-Ca. EHNA (30 mu M) also blocked the inhibitory effect of NO donors, such as sodium nitroprusside (1 mM) and 3-morpholinosyd nonimine (30 mu M), on isoprenaline-stimulated I-Ca. In addition, EHNA dose-dependently (IC50 approximate to 4-5 mu M) inhibited the cGMP-in duced stimulation of PDE activity in frog ventricle particulate fracti on, as well as purified soluble cGS-PDE. However, EHNA (up to 30 mu M) did not modify the activities of three other purified soluble PDE iso forms. Moreover, EHNA did not change the K-a (40 nM) for cGMP activati on of cGS-PDE, which suggests that EHNA does not inhibit cGS-PDE by di splacing cGMP from the allosteric regulator site. Because adenosine di d not mimic the effects of EHNA on I-Ca or PDE activity, it is unlikel y that the effects of EHNA are due to adenosine deaminase inhibition. We conclude that EHNA acts primarily to inhibit cGS-PDE in intact card iac myocytes. This compound should be useful in evaluating the physiol ogical role of cGS-PDE in various tissues.