Downregulation of cardiac guanosine 5'-triphosphate-binding proteins in right atrium and left ventricle in pacing-induced congestive heart failure.

Abstract

The extent to which congestive heart failure (CHF) is dependent upon increased levels of the cardiac inhibitory GTP-binding protein (Gi), and the impact of CHF on the cardiac stimulatory GTP-binding protein (Gs) and mechanisms by which Gs may change remain unexplored. We have addressed these unsettled issues using pacing-induced CHF in pigs to examine physiological, biochemical, and molecular features of the right atrium (RA) and left ventricle (LV). CHF was associated with an 85±20% decrease in LV segment shortening (P < 0.001) and a 3.5-fold increase (P = 0.006) in the ED5, for isoproterenol-stimulated heart rate responsiveness. Myocardialfg-adrenergic receptor number was decreased 54% in RA (P = 0.004) and 57% in LV (P < 0.001), and multiple measures of adenylyl cyclase activity were depressed 49±8% in RA (P < 0.005), and 44±9% in LV (P < 0.001). Quantitative immunoblotting established that Gi and Gs were decreased in RA (Gi: 59% reduction; P < 0.0001; Gs: 28% reduction; P < 0.007) and LV (Gi: 35% reduction; P < 0.008; Gs: 28% reduction; P < 0.01 ) after onset of CHF. Reduced levels of Gi and Gs were confirmed by ADP ribosylation studies, and diminished function of Gs was established in reconstitution studies. Steady state levels for Gsa mRNA were increased in RA and unchanged in LV, and significantly more GSa was found in the supernatant (presumably cytosolic) fraction in RA and LV membrane homogenates after CHF, suggesting that increased Gs degradation, rather than decreased Gs synthesis, is the mechanism by which Gs is downregulated. We conclude that cardiac Gi content poorly predicts adrenergic responsiveness or contractile function, that decreased Gs is caused by increased degradation rather than decreased synthesis, and that alterations in fI-adrenergic receptors, adenylyl cyclase, and GTP-binding proteins are uniform in RA and LV in this model of congestive heart failure. (J. Clin. Invest. 1993. 91:939-949.)

Reduced beta-adrenergic receptor activation decreases G-protein expression and beta-adrenergic receptor kinase activity in porcine heart.

“…We have previously reported reduced cardiac Gia2 mRNA and protein content in a porcine model of heart failure (5,18,19). Thus, chronic reduction in 13-adrenergic receptor activation (bisoprolol treatment) and heart failure have similar effects upon Gia2 expression in the porcine heart.…”

“…Assessment of as and ai2 subunits of Gs and Gia2 was conducted using standard SDS-PAGE and immunoblotting techniques (5,20). Briefly, 100 Mg of protein from each supematant and resuspended pellet fraction of a 45,000-g centrifugation of crude myocardial homogenate derived from appropriate transmural samples was electrophoresed on a 10% denaturing gel for 4 h at 30 mA constant current.…”

“…Assessment of left ventricular /6-adrenergic receptor kinase, content was conducted using standard SDS-PAGE and immunoblotting techniques (5,20). An antibody specific for /3-adrenergic receptor kinase, and purified bovine ,8-adrenergic receptor kinase, were provided by Dr. J. L.…”

“…Previous studies from our laboratory and others have shown that sustained B-adrenergic receptor activation can influence the expression of not only cell surface /-adrenergic receptors, but also Gs and Gi in the heart (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Heart failure, a condition characterized in part by systemic neurohumoral adrenergic activation, is associated with reduced /3-adrenergic receptor expression at mRNA and protein levels (4, 5, [15][16][17] and, in some studies, with alterations in the expression of cardiac G-proteins (4,7,8,13,18).…”

Effects of Angiotensin-Converting Enzyme Inhibition and Angiotensin II Type 1 Receptor Blockade on β-Adrenoceptor Signaling in Heart Failure Produced by Myocardial Infarction in Rabbits: Reversal of Altered Expression of β-Adrenoceptor Kinase and Giα

“…Increased plasma norepinephrine due to the high sympathetic tone activates ␤-adrenoceptors responsible for maintaining inotropy and cardiac output in the compensated stages of HF. This adrenergic overactivation in HF, however, leads to abnormal myocardial ␤-adrenoceptor signaling including ␤-adrenoceptor down-regulation, uncoupling of ␤-adrenoceptor and the stimulatory G protein (G s ), and decreased adenylate cyclase activity (Bristow et al, 1986;Roth et al, 1993;Brodde et al, 1995). An important aspect of this defective myocardial ␤-adrenoceptor signaling is the fact that agonist occupation of ␤-adrenoceptors at high concentrations activates ␤ARK1, which phosphorylates the receptors (Hausdorff et al, 1990).…”