DIVERSE G-PROTEIN AND BETA-ADRENERGIC-RECEPTOR MESSENGER-RNA EXPRESSION IN NORMAL AND FAILING PORCINE HEARTS

Right atrial and left ventricular homogenates have similar protein composition and beta-adrenergic receptor (beta-AR) numbers, but the right atrium has > 58% less adenylyl cyclase activity than the left ventricle. Associated with distinctive patterns of adenylyl cyclase activities are differences in G protein regulation between the two chambers. Compared with the left ventricle, the right atrium has 74% less G(s) alpha mRNA (P < 0.0001) and 83% less G alpha(i-2) mRNA(P < 0.002). When hearts are rapidly paced to produce heart failure, the left ventricle shows significant reductions in mRNA expression for both Gs(a)lpha and G alpha(i-2). However, the right atrium shows increased G(s) alpha and G alpha(i-2) mRNA expression. Despite divergent mRNA expression, G(s) alpha and G alpha(i-2) protein expression is downregulated in both chambers in heart failure. In contrast, both chambers have similar beta(1)- and beta(2)-adrenergic receptor mRNA contents, and there is a selective reduction of beta(1)-adrenergic receptor protein and mRNA in response to heart failure. Thus G protein and beta-AR mRNA regulation is regionally diverse in the heart. Physiological and anatomic differences between the right atrium and the left ventricle may dictate distinct patterns of adrenergic signaling and adaptations to stress.