Decreased stimulatory guanosine triphosphate binding protein in dogs with pressure-overload left ventricular failure

Abstract

Alterations in the level and function of the stimulatory guanyl nucleotide binding protein (G(s)) from the cardiac sarcolemma were examined in a canine model of heart failure. The present study is based on our previous investigations that demonstrated both a loss of β-adrenergic agonist high-affinity binding sites and a decreased adenylate cyclase activity in sarcolemma from failing hearts. Using cholera toxin and [32P]NAD, we labeled the alpha subunit of G(s) (G(sα)) and found a 59% reduction in the level of this protein. Further, a 50% reduction in G(s) activity was noted in a reconstitution assay utilizing membranes from the mouse S49 lymphoma cell line cyc-, which is deficient in G(s). These data suggest that, in this model of pressure-overload left ventricular failure, the acquired defect in the β-adrenergic receptor/adenylate cyclase system involves a deficiency in the coupling protein G(s). Such an abnormality may explain the decreased adrenergic responsiveness of the failing left ventricle.