CGMP-STIMULATED CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE REGULATES THE BASAL CALCIUM CURRENT IN HUMAN ATRIAL MYOCYTES

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 fro g, human, and porcine heart with an apparent K-i value of similar to 1 mu M 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. Mel. Pharmacol. 48 :121-130; Podzuweit, T., P. Nennstiel, and A. Muller. 1995. Cell. Sign alling. 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 mu M EHNA induced an increase in the amplitude o f basal I-Ca (similar to 80% at 1 mu M) without modification of the cu rrent-voltage or inactivation curves. The maximal stimulatory effect o f EHNA on I-Ca was comparable in amplitude with the maximal effect of isoprenaline (1 mu M), and the two effects were not additive. The effe ct of EHNA was not a result of adenosine deaminase inhibition, since 2 '-deoxycoformycin (1-30 mu M), another adenosine deaminase inhibitor w ith no effect on PDE2, or adenosine (1-10 mu M) did not increase I-Ca. In the absence of intracellular GTP, the substrate of guanylyl cyclas e, EHNA did not increase I-Ca. However, under similar conditions, intr acellular perfusion with 0.5 mu M cGMP produced an 80% increase in I-C a. As opposed to human cardiomyocytes, EHNA (1-10 mu M) did not modify I-Ca in isolated rat ventricular and atrial myocytes. We conclude tha t basal I-Ca is controlled by PDE2 activity in human atrial myocytes. Both PDE2 and PDES may contribute to keep the cyclic nucleotides conce ntrations at minimum in the absence of adenylyl and/or guanylyl cyclas e stimulation.