sGCα1 mediates the negative inotropic effects of NO in cardiac myocytes independent of changes in calcium handling

Cawley SM, Kolodziej S, Ichinose F, Brouckaert P, Buys ES, Bloch KD. sGC alpha(1) mediates the negative inotropic effects of NO in cardiac myocytes independent of changes in calcium handling. Am J Physiol Heart Circ Physiol 301: H157-H163, 2011. First published May 2, 2011; doi:10.1152/ajpheart.01273.2010.-In the heart, nitric oxide (NO) modulates contractile function; however, the mechanisms responsible for this effect are incompletely understood. NO can elicit effects via a variety of mechanisms including S-nitrosylation and stimulation of cGMP synthesis by soluble guanylate cyclase (sGC). sGC is a heterodimer comprised of a beta(1)- and an alpha(1)- or alpha(2)-subunit. sGC alpha(1)beta(1) is the predominant isoform in the heart. To characterize the role of sGC in the regulation of cardiac contractile function by NO, we compared left ventricular cardiac myocytes (CM) isolated from adult mice deficient in the sGC alpha(1)-subunit (sGC alpha(-/-)(1)) and from wild-type (WT) mice. Sarcomere shortening under basal conditions was less in sGC alpha(-/-)(1) CM than in WT CM. To activate endogenous NO synthesis from NO synthase 3, CM were incubated with the beta(3)-adrenergic receptor (beta(3)-AR) agonist BRL 37344. BRL 37344 decreased cardiac contractility in WT CM but not in sGC alpha(-/-)(1) myocytes. Administration of spermine NONOate, an NO donor compound, did not affect sarcomeric shortening in CM of either genotype; however, in the presence of isoproterenol, addition of spermine NONOate reduced sarcomere shortening in WT but not in sGC alpha(-/-)(1) CM. Neither BRL 37344 nor spermine NONOate altered calcium handling in CM of either genotype. These findings suggest that sGC alpha(1) exerts a positive inotropic effect under basal conditions, as well as mediates the negative inotropic effect of beta(3)-AR signaling. Additionally, our work demonstrates that sGC alpha(1)beta(1) is required for NO to depress beta(1)/beta(2)-AR-stimulated cardiac contractility and that this modulation is independent of changes in calcium handling.