Soluble guanylyl cyclase is a target of angiotensin II-induced nitrosative stress in a hypertensive rat model. Am J Physiol Heart Circ Physiol 303: H597-H604, 2012. First published June 22, 2012; doi:10.1152/ajpheart.00138.2012 by activating soluble guanylyl cyclase (sGC) is involved in vascular homeostasis via induction of smooth muscle relaxation. In cardiovascular diseases (CVDs), endothelial dysfunction with altered vascular reactivity is mostly attributed to decreased NO bioavailability via oxidative stress. However, in several studies, relaxation to NO is only partially restored by exogenous NO donors, suggesting sGC impairment. Conflicting results have been reported regarding the nature of this impairment, ranging from decreased expression of one or both subunits of sGC to heme oxidation. We showed that sGC activity is impaired by thiol S-nitrosation. Recently, angiotensin II (ANG II) chronic treatment, which induces hypertension, was shown to generate nitrosative stress in addition to oxidative stress. We hypothesized that S-nitrosation of sGC occurs in ANG II-induced hypertension, thereby leading to desensitization of sGC to NO hence vascular dysfunction. As expected, ANG II infusion increases blood pressure, aorta remodeling, and protein S-nitrosation. Intravital microscopy indicated that cremaster arterioles are resistant to NO-induced vasodilation in vivo in anesthetized ANG II-treated rats. Concomitantly, NO-induced cGMP production decreases, which correlated with S-nitrosation of sGC in hypertensive rats. This study suggests that S-nitrosation of sGC by ANG II contributes to vascular dysfunction. This was confirmed in vitro by using A7r5 smooth muscle cells infected with adenoviruses expressing sGC or cysteine mutants: ANG II decreases NO-stimulated activity in the wild-type but not in one mutant, C516A. This result indicates that cysteine 516 of sGC mediates ANG II-induced desensitization to NO in cells. nitric oxide resistance; vascular dysfunction; oxidative stress; hypertension SOLUBLE GUANYLYL CYCLASE (sGC) is the main receptor for nitric oxide (NO) and the enzyme responsible for the conversion of GTP into cGMP. As such, the NO-receptor sGC is crucially involved in the physiology of the cardiovascular system by modulating vessel tone. Indeed, mice lacking this receptor are hypertensive (5). Oxidative stress is associated with cardiovascular diseases (CVDs) such as hypertension, atherosclerosis, and diabetes. Most oxidative CVDs are accompanied by endothelial dysfunction and impaired vascular reactivity with decreased NO bioavailability. Nonetheless, it should be pointed out that oxidative stress affects as well the smooth muscle cell (SMC) layers where sGC is expressed. It has been reported that reactive oxygen species (ROS) alter sGC expression and activity (19,25,29). We (21) have previously shown that in vitro and in vivo S-nitrosation of sGC impairs its ability to be activated by NO. In particular, we established that infusion of low therapeutic doses of nitroglycerin in rats for 3 days i...

No abstract

BackgroundGuanylyl cyclase, a heme‐containing α1β1 heterodimer (GC1), produces cGMP in response to Nitric oxide (NO) stimulation. The NO‐GC1‐cGMP pathway negatively regulates cardiomyocyte contractility and protects against cardiac hypertrophy–related remodeling. We recently reported that the β1 subunit of GC1 is detected at the intercalated disc with connexin 43 (Cx43). Cx43 forms gap junctions (GJs) at the intercalated disc that are responsible for electrical propagation. We sought to determine whether there is a functional association between GC1 and Cx43 and its role in cardiac homeostasis.Methods and Results GC1 and Cx43 immunostaining at the intercalated disc and coimmunoprecipitation from membrane fraction indicate that GC1 and Cx43 are associated. Mice lacking the α subunit of GC1 (GCα1 knockout mice) displayed a significant decrease in GJ function (dye‐spread assay) and Cx43 membrane lateralization. In a cardiac‐hypertrophic model, angiotensin II treatment disrupted the GC1‐Cx43 association and induced significant Cx43 membrane lateralization, which was exacerbated in GCα1 knockout mice. Cx43 lateralization correlated with decreased Cx43‐containing GJs at the intercalated disc, predictors of electrical dysfunction. Accordingly, an ECG revealed that angiotensin II–treated GCα1 knockout mice had impaired ventricular electrical propagation. The phosphorylation level of Cx43 at serine 365, a protein‐kinase A upregulated site involved in trafficking/assembly of GJs, was decreased in these models.Conclusions GC1 modulates ventricular Cx43 location, hence GJ function, and partially protects from electrical dysfunction in an angiotensin II hypertrophy model. Disruption of the NO‐cGMP pathway is associated with cardiac electrical disturbance and abnormal Cx43 phosphorylation. This previously unknown NO/Cx43 signaling could be a protective mechanism against stress‐induced arrhythmia.

No abstract