cGMP-stimulated cyclic nucleotide phosphodiesterase regulates the basal calcium current in human atrial myocytes

Abstract

EHNA (Erythro-9-[2-hydroxy-3-nonyl]adenine) is a well-known inhibitor of adenosine deaminase. Recently, EHNA was shown to block the activity of purified soluble cGMP-stimulated phosphodiesterase (PDE2) from frog, human, and porcine heart with an apparent K(i) value of ~ 1 μM and with negligible effects on Ca2+/calmodulin PDE (PDE1), cGMP-inhibited PDE (PDE3), and low K(m) cAMP-specific PDE (PDE4) (Mery, P.F., C. Pavoine, F. Pecker, and R. Fischmeister. 1995. Mol. Pharmacol. 48:121-130; Podzuweit, T., P. Nennstiel, and A. Muller. 1995. Cell. Signalling. 7:733-738). To investigate the role of PDE2 in the regulation of cardiac L-type Ca2+ current (I(Ca)), we have examined the effect of EHNA on I(Ca) in freshly isolated human atrial myocytes. Extracellular application of 0.1-10 μM EHNA induced an increase in the amplitude of basal I(Ca) (~ 80% at 1 μM) without modification of the current-voltage or inactivation curves. The maximal stimulatory effect of EHNA on I(Ca) was comparable in amplitude with the maximal effect of isoprenaline (1 μM), and the two effects were not additive. The effect of EHNA was not a result of adenosine deaminase inhibition, since 2'- deoxycoformycin (1-30 μM), another adenosine deaminase inhibitor with no effect on PDE2, or adenosine (1-10 μM) did not increase I(Ca). In the absence of intracellular GTP, the substrate of guanylyl cyclase, EHNA did not increase I(Ca). However, under similar conditions, intracellular perfusion with 0.5 μM cGMP produced an 80% increase in I(Ca). As opposed to human cardiomyocytes, EHNA (1-10 μM) did not modify I(Ca) in isolated rat ventricular and atrial myocytes. We conclude that basal I(Ca) is controlled by PDE2 activity in human atrial myocytes. Both PDE2 and PDE3 may contribute to keep the cyclic nucleotides concentrations at minimum in the absence of adenylyl and/or guanylyl cyclase stimulation.