Regulation of cardiac calcium current by NO and cGMP-modulating agents

Abstract

Several effects of nitric oxide (NO) on the control of L-type calcium current (ICa) and of calcium handling in cardiomyocytes have been described. Cardiomyocytes have been shown to express in different conditions all types of nitric oxide synthases (NOS), but the role of NO in the regulation of calcium current remains controversial. Previously, we have shown in guinea pig ventricular cells a stimulatory effect of NOS inhibitors on ICa. Here we investigate the intracellular mechanisms involved in the putative inhibitory role of NO on basal ICa in ventricular cells. The stimulatory effect of the NOS inhibitor NG-monomethyl-L-arginine (L-NMMA) (1 mM) was present also in calcium transient measurements, but only after a preincubation with L-arginine (L-arg, 0.1 mM). The nitric oxide scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO, 0.5 mM) increased peak ICa in a similar manner to NOS inhibitors in whole-cell voltage-clamp experiments. Also ODQ (1H-[1,2,4]oxidiazolo[4,3-a]quinoxaline-1-one, 0.1 mM), a specific inhibitor of a target of NO, the soluble guanylate cyclase, was able to stimulate ICa. The block of type II phosphodiesterase (cGMP-activated) by EHNA (erythro-9-[2-hydroxy-3-nonylladenine, 30 microM) exerted a similar effect on ICa as PTIO and ODQ. Carbachol (CCh, 1 microM) was able to revert the stimulatory effect on ICa observed with PTIO, ODQ, and EHNA. We propose that the increase of basal ICa in guinea pig cardiomyocytes previously observed with L-NMMA depends on the removal of a tonic NO inhibition. This increase of ICa is mimicked by blocking at different steps the cGMP-cascade activated by NO, suggesting a NO-guanylate cyclase mechanism in the basal control of ventricular calcium current.

Cardiac Nitric Oxide Synthase 1 Regulates Basal and β-Adrenergic Contractility in Murine Ventricular Myocytes

“…These data suggest that the main effect of NOS1 in intact myocytes may not be at the level of the SERCA2a but at the L-type calcium channel. This is consistent with recent work indicating that myocardial NO production can tonically inhibit the L-type calcium current in frog 17 and guinea pig 18 cardiac myocytes and is consistent with experiments showing that NOS1-derived NO suppresses voltage-sensitive calcium entry in neurons. 19 In addition, increasing consideration is being given to the notion that local concentrations of NO govern subcellular processes in microdomains.…”

Conditional Neuronal Nitric Oxide Synthase Overexpression Impairs Myocardial Contractility

“…As suggested by Gallo et al nNOS-derived NO could be acting via the guanylate cyclase/ cyclic GMP second messenger pathway. 27 In agreement with these findings, 8-BrcGMP has been shown to inhibit I Ca,L in ferret right ventricular myocytes, 28 and the cGMP dependent protein kinase (PKG) has been reported to cause a 40% inhibition of I Ca,L in rat ventricular myocytes. 29 Indeed, we found increased cGMP levels in the nNOS overexpressing myocytes.…”

Neuronal Nitric Oxide Synthase Protects Against Myocardial Infarction-Induced Ventricular Arrhythmia and Mortality in Mice

“…Moreover, NO also has been reported to modulate the L-type Ca 2ϩ channel via cGMP. 31,33 Thus, although S-nitrosylation is an important contributor to the altered Ca 2ϩ handling and ventricular arrhythmia in nNOS…”