Increased levels of inhibitory G protein in myocardium with heart failure

To identify any differences in inhibitory G protein (Gi) attributable to species or the cause of heart failure, we studied the changes in this protein in different animal models of heart failure: 1) different species; rats vs. hamsters (F1B) with cardiomyopathy induced by adriamycin (ADR) and 2) different etiologies; rats with ischemic heart failure (IHD) due to coronary artery ligation vs. rats with cardiomyopathy induced by ADR and F1B (20-week-old) hamsters with cardiomyopathy induced by ADR vs Syrian hamsters BIO 14.6 (40-week-old) with genetic cardiomyopathy, using Western blotting methods and ADP-ribosylation. We also sought to determine whether changes in the amount of Gi protein reflected the regulation of adenylate cyclase. The amount of immunodetectable Gi rose by 35% (p < 0.05) in ADR rats, 25% (p < 0.05) in ADR hamsters, 15% (p < 0.05) in IHD rats, and 28% (p < 0.05) in BIO 14.6 hamsters, as compared with control rats, F1B (20-week-old) hamsters, sham-operated control rats, and F1B (40-week-old) hamsters, respectively. Assessment of Gi by pertussis toxin-catalyzed ADP-ribosylation revealed increases in Gi of 24% (p < 0.05) in ADR rats and of 44% (p < 0.05) in BIO 14.6 hamsters, as compared with their respective controls. Gi function, as assayed by the acetylcholine-induced inhibition of adenylate cyclase, also increased. Thus, Gi protein appears to contribute to the changes in signal transduction in myocardium with heart failure.