G-protein mediated inhibitory effect of a nitric oxide donor on the L-type Ca 2+ current in rat ventricular myocytes
Abstract
The role of the cGMP pathway in the modulation of the cardiac L-type Ca2+ current (ICa,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 ICa,L. However, DEANO (100 μM) inhibited ICa,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 ICa,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 ICa,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 ICa,L.
Intracellular dialysis with exogenous cAMP (10-100 μM) blunted the inhibitory effect of DEANO (10 and 100 μM) on ICa,L. SNAP and SNP also had no effect on the cAMP-stimulated ICa,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 ICa,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.
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