Inhibition of renin-angiotensin system (RAS) reduces ventricular tachycardia risk by altering connexin43

Abstract

Renin-angiotensin system (RAS) activation is associated with arrhythmias. We investigated the effects of RAS inhibition in cardiac-specific angiotensin-converting enzyme (ACE) overexpression (ACE 8/8) mice, which exhibit proclivity to ventricular tachycardia (VT) and sudden death because of reduced connexin43 (Cx43). ACE 8/8 mice were treated with an ACE inhibitor (captopril) or an angiotensin receptor type-1 blocker (losartan). Subsequently, electrophysiological studies were performed, and the hearts were extracted for Cx43 quantification using immunoblotting, immunohistochemistry, fluorescent dye spread method, and sodium current quantification using whole cell patch clamping. VT was induced in 12.5% of captopril-treated ACE 8/8 and in 28.6% of losartan-treated mice compared to 87.5% of untreated mice (P<0.01). Losartan and captopril treatment increased total Cx43 2.4-fold (P=0.01) and the Cx43 phosphorylation ratio 2.3-fold (P=0.005). Treatment was associated with a recovery of gap junctional conductance. Survival in treated mice improved to 0.78 at 10 weeks (95% confidence interval 0.64 to 0.92), compared to the expected survival of less than 0.50. In a model of RAS activation, arrhythmic risk was correlated with reduced Cx43 amount and phosphorylation. RAS inhibition resulted in increased total and phosphorylated Cx43, decreased VT inducibility, and improved survival.

Myofibroblasts cause heterogeneous Cx43 reduction and are unlikely to be coupled to myocytes in the healing canine infarct

“…Hearts were rapidly removed at either 48 h or 5 day postcoronary occlusion, and the left ventricle was dissected free and placed in warm oxygenated saline, epicardial side up. Dye spread was done as described previously (13,24). With a 26-gauge needle a pinhole was made and 2.5% Lucifer Yellow in 150 mM lithium chloride was pipetted onto the surface.…”

Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

“…Prolonged stimulation of cardiomyocytes with isoprenaline increases Cx43 expression through activation of Erk1/2 (Salameh et al, 2013;Salameh et al, 2009); however, in co-cultures of cardiomyocytes and fibroblasts, paracrine factors released by fibroblasts suppress the isoprenaline-induced increase in Cx43 expression in cardiomyocytes (Pedrotty et al, 2009;Salameh et al, 2013). Such suppression can partially be reversed by blocking angiotensin II or PKC (Pedrotty et al, 2009), and in cardiac tissue from mice, inhibition of the renin angiotensin system increases Cx43 expression (Iravanian et al, 2011). …”

Mechanisms of Sudden Cardiac Death

“…The activation of cSrc leads to Cx43 downregulation, impaired gap junction function, slowed cardiac conduction and increased incidence of ventricular arrhythmias and SCD. 35, 257 The downregulation of Cx43 and increased risk for arrhythmias in ACE8/8 mice are alleviated by pharmacologic inhibition of RAS 258 and cSrc. 257 It has been shown that increased myocardial p-cSrc leads to Cx43 reduction through the competition between p-cSrc and Cx43 for the binding with zonula occludens-1, a scaffolding protein at the intercalated disk, resulting in Cx43 destabilization and degradation.…”