Abstract 1506: Upregulation of Cardiac AT 1 Receptor Signaling Inhibits Myocyte Contractile Performance, [Ca 2+ ] i Transient, and Ca 2+ Current in Alcoholic Dogs: Insights into the Underlying Molecular Mechanism

Abstract

Background. Chronic alcohol ingestion is accompanied by sustained renin-angiotensin system (RAS) activation followed by progressive left ventricular (LV) myocyte dysfunction. This suggests a role for angiotensin II (AII) in the development of alcoholic cardiomyopathy (ACM). We tested the hypothesis that chronic alcohol intake may cause upregulation of AII AT 1 receptors and altered cardiac inotropic response to AII stimulation, thus contributing to the development of ACM. Methods. We compared LV myocyte AT 1 - and AT 2 -receptor mRNA and protein levels, myocyte contractile function, [Ca 2+ ] i transients ([Ca 2+ ] iT ), and Ca 2+ current (I Ca,L ) in response to AII (10 −6 M) in 16 instrumented dogs over 6 months. Eight animals received alcohol (once per day orally, providing 33% of total daily caloric intake), and eight were controls. Myocytes were isolated from LV myocardial biopsy tissues. Results . Compared with controls, the alcoholic myocytes showed increased AT 1 mRNA (0.69 vs 0.33) and protein levels (0.79 vs 0.37) ( p <0.01). Conversely, AT 2 mRNA (0.18 vs 0.16) and protein concentration (0.16 vs 0.14) were relatively unchanged. Importantly, in alcoholic myocytes, the increased AT 1 receptors were associated with altered myocyte inotropic response to AII. In control myocytes, superfusion of AII (10 −6 M) increased myocyte systolic amplitude (SA, 14.9 vs 12.4%) and the maximum rate of shortening (dL/dt max , 203.1 vs 153.9 μm/s) accompanied by significant increases in [Ca 2+ ] iT (1.52 vs 1.21) and I Ca,L (4.0 vs 3.3 pA/pF). In alcoholic myocytes, this positive response was reversed. AII caused significant decreases in SA (3.4 vs 5.8 %), dL/dt max (50.5 vs 78.9 μm/s), and the maximum rate of relaxation (dR/dt max, 37.5 vs 59.6 μm/s) associated with reduced [Ca 2+ ] iT (0.86 vs 1.12) and I Ca,L (1.5 vs 2.1 pA/pF) ( p <0.05). These AII-induced changes in alcoholic myocytes were abolished by incubation of alcoholic myocytes with an AT 1 receptor blocker, losartan (10 −5 M), or pretreatment with a G i inhibitor, PTX (2 μg/ml, 36°C, 5h). Conclusions. In a canine model, chronic alcohol consumption produces upregulation of LV myocyte AII AT 1 receptors and alters myocyte functional response to AII stimulation, which may promote the development of ACM.