Cyclic GMP regulation of the L-type Ca2+ channel current in human atrial myocytes

1. The regulation of the L-type Ca2+ current (I-Ca) by intracellular cGMP w as investigated in human atrial myocytes using the whole-cell patch-clamp t echnique 2. Intracellular application of 0.5 muM cGMP produced a strong stimulation of basal I-Ca (+64 +/- 5%, n = 60), whereas a 10-fold higher cGMP concentra tion induced a 2-fold smaller increase (+36 +/- 8%, n = 35). 3. The biphasic response of I-Ca to cGMP was not mimicked by the cGMP-depen dent protein kinase (PKG) activator 8-bromoguanosine 3 ' ,5 ' cyclic monoph osphate (8-bromo-cGMP, 0.5 or 5 muM), and was not affected by the PKG inhib itor KT 5823 (100nM). 4. In contrast, cGMP stimulation of I-Ca was abolished by intracellular per fusion with PKI (10 muM) a selective inhibitor of the cAMP-dependent protei n kinase (PKA). 5. Selective inhibition of the cGMP-inhibited phosphodiesterase (PDE3) by; extracellular cilostamide (100 nM) strongly enhanced basal I-Ca in control conditions (+78 +/- 13%, n = 7) but had only a marginal effect in the prese nce of intracellular cGMP (+22 +/- 7% in addition to 0.5 muM cGMP, n = 11; +20 +/- 22% in addition to 5 muM cGMP, n = 7) 6. Application of erythro-9-[2-hydroxy-3-nonyl]adenine (EHNA, 30 muM), a se lective inhibitor of the cGMP-stimulated phosphodiesterase (PDE2), fully re versed the secondary inhibitory effect of 5 muM cGMP on I-Ca (+99 +/- 16% s timulation, n = 7). 7. Altogether, these data indicate that intracellular cGMP regulates basal I-Ca in human atrial myocytes in a similar manner to NO donors. The effect of cGMP involves modulation of the cAMP level and PKA activity via opposite actions of the nucleotide on PDE2 and PDE3.