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.