Diverse G protein and β-adrenergic receptor mRNA expression in normal and failing porcine hearts

Right atrial and left ventricular homogenates have similar protein composition and β-adrenergic receptor (β-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)α mRNA (P < 0.0001) and 83% less Gα(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 G(s)α and Gα(i-2). However, the right atrium shows increased G(s)α and Gα(i-2) mRNA expression. Despite divergent mRNA expression, G(s)α and Gα(i-2) protein expression is down-regulated in both chambers in heart failure. In contrast, both chambers have similar β₁- and β₂-adrenergic receptor mRNA contents, and there is a selective reduction of β₁-adrenergic receptor protein and mRNA in response to heart failure. Thus G protein and β-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.