G protein-mediated inhibitory effect of a nitric oxide donor on the L-type Ca2+ current in rat ventricular myocytes

The role of the cGMP pathway in the modulation of the cardiac L-type Ca 2+ current ( I Ca,L ) by nitric oxide (NO) was examined in rat ventricular myocytes. The NO donors DEANO, SIN-1, SNP, SNAP and GSNO had no significant effects on basal I Ca,L . However, DEANO (100 μM) inhibited I Ca,L after the current had been previously stimulated by either isoprenaline (Iso, 1–10 nM), a β-adrenergic agonist, or isobutylmethyl-xanthine (IBMX, 10–80 μM), a wide spectrum phosphodiesterase (PDE) inhibitor. The anti-adrenergic effect of DEANO on I Ca,L was not mimicked by other NO donors (SIN-1, SNAP and SPNO). The NO-sensitive guanylyl cyclase inhibitor ODQ (10 μM), antagonized the inhibitory effect of DEANO on I Ca,L . Likewise, inhibitors of the cGMP-dependent protein kinase (cG-PK), Rp-8-chloro-phenylthio-cGMP (10 μM) and KT5823 (0.1 and 0.3 μM), also abolished the inhibitory effect of DEANO on Iso (1–;10 nM)-stimulated I Ca,L . Intracellular dialysis with exogenous cAMP (10–100 μM) blunted the inhibitory effect of DEANO (10 and 100 μM) on I Ca,L . SNAP and SNP also had no effect on the cAMP-stimulated I Ca,L . Pre-treatment of the myocytes with pertussis toxin (0.5 μg ml −1 , 4–6 h at 37 °C) eliminated the inhibitory effect of DEANO (100 μM) on I Ca,L , in the presence of either Iso (0.01 and 1 nM) or IBMX (10–80 μM). These results demonstrate that DEANO produces anti-adrenergic effects in rat ventricular myocytes. This effect of DEANO occurs in a cGMP-dependent manner, and involves activation of cG-PK and regulation of a pertussis toxin-sensitive G protein.