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

1. The role of the cGMP pathway in the modulation of the cardiac L-type Ca2+ current (I-Ca,I-L) by nitric oxide (NO) was examined in rat ventricular myocytes. 2. The NO donors DEANO, SIN-1, SNP, SNAP and GSNO had no significant effects on basal I-Ca,(L). However, DEANO (100 muM) inhibited I-Ca,(L) after the current had been previously stimulated by either isoprenaline (Iso, 1-10 nM), a beta -adrenergic agonist, or isobutylmethylxanthine(IBMX, 10-80 muM), a,vr ide spectrum phosphodiesterase (PDE) inhibitor. 3. The anti-adrenergic effect of DEANO on I-Ca,I-L was not mimicked by other NO donors (SIN-1, SNAP and SPNO). 4. The NO-sensitive guanylyl cyclase inhibitor ODQ (10 muM), 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 muM) and KT5823 (0.1 and 0.3 muM), also abolished the inhibitory effect of DEANO on ISO (1-10 nM)-stimulated I-Ca,(L). 5. Intracellular dialysis with exogenous cAMP (10-100 muM) blunted the inhibitory effect of DEANO (10 and 100 muM) on I-Ca,I-L. SNAP and SNP also had no effect on the caMP-stimulated I-Ca,(L). 6. Pre-treatment of the myocytes with pertussis: toxin (0.5 mug ml(-1) 4-6 h at 37 degreesC) eliminated the inhibitory effect of DEANO (100 muM) on I-Ca,(L), in the presence of either Iso (0.01 and 1 nM) or IBMX (10-80 muM). 7. These results demonstrate that:DEANO produces anti-adrenergic effects in rat ventricular myocytes. This: effect of DF,ANO occurs in a cGMP-dependent manner, and involves activation of cG-PK and regulation of a pertussis toxin-sensitive G protein.