G protein expression and adenylate cyclase regulation in ventricular cardiomyocytes from STZ-diabetic rats

Abstract

Isolated adult ventricular cardiomyocytes have been used to study the effects of insulin-deficient diabetes on the expression of cardiac G protein alpha-subunits. Immunoblot analysis of plasma membranes revealed the presence of three different Gs proteins with molecular masses of 45, 47, and 52 kDa. Furthermore, cardiomyocytes were found to contain Gi-2 (41 kDa) and G(o) (39 kDa). Heart cells from streptozotocin-diabetic rats exhibited an unaltered expression of the Gs proteins, whereas Gi-2 and G(o) were reduced by 58 +/- 2 and 27 +/- 11%, respectively. In cells from diabetic rats, adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in response to isoproterenol decreased by approximately 30% at agonist concentrations of 10(-7) to 10(-5) M, with an unaltered maximum stimulation by forskolin. Treatment of cardiomyocytes with pertussis toxin resulted in an incremental increase of isoproterenol-stimulated cAMP formation, which was significantly lower in cardiac myocytes from streptozotocin-diabetic animals (19.2 +/- 1.7 vs. 11.5 +/- 2.4 pmol cAMP.5 x 10(4) cells-1 times 10 min-1). The inhibition of the isoproterenol-induced cAMP accumulation by carbachol in the intact cell was not altered in streptozotocin-diabetes. In conclusion, our data show that insulin-deficient diabetes is associated with a reduced expression and concomitant functional loss of Gi in ventricular cardiomyocytes. Receptor-mediated inhibition of adenylate cyclase remains unaffected by this process, whereas the beta-adrenergic stimulatory pathway involves an additional defect upstream of the adenylate cyclase/G protein system.

Increased expression of Gαq protein in the heart of streptozotocin-induced diabetic rats

“…Our result on the expression of Gαs, not affected by insulin deficiency, was agreeable with the findings of Wichelhaus et al (1994) in the heart ventricles of streptozotocin-induced diabetic rat. The result of no change of Gαi expression in heart of diabetic rat was agreeable with the findings of Fu et al (1994), but differed from the result of Wichelhaus et al (1994). The G protein-coupled signaling pathways initiate a cascade of enzyme activation, such as PKA, PLC, PKC, CaM kinase etc.…”

Gi proteins mediate activation of the canonical hedgehog pathway in the myocardium

“…Streptozotocin-treated mice exhibit decreased levels of G␣ i proteins in the myocardium, similar to the human diabetic heart (19,32). In these animals, the normal upregula- Fig.…”

Autocrine Action of Adiponectin on Human Fat Cells Prevents the Release of Insulin Resistance-Inducing Factors

“…After incubation for 2 h at 4°C the suspension was centrifuged at 10,000g for 10 min. Thereafter, total cell lysates were separated by SDS-PAGE using gradient (8 -18%) horizontal gels and transferred to polyvinylidene fluoride filters in a semidry blotting apparatus (25). For detection of p-Akt, Akt, p-GSK3␣/␤, and GSK3␣/␤, filters were blocked with Tris-buffered saline containing 0.1% Tween-20 and 5% nonfat dry milk and subsequently incubated overnight with a 1:1,000 dilution of appropriate antibodies.…”