G protein expression and adenylate cyclase regulation in ventricular cardiomyocytes from STZ-diabetic rats.
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.
Wichelhaus
A
A
Laboratory of Molecular Cardiology, Diabetes Research Institute, Düsseldorf, Germany.
Russ
M
M
Petersen
S
S
Eckel
J
J
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D016922:Cellular Senescence; D000242:Cyclic AMP / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism* / Q000473:pathology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006352:Heart Ventricles; D008297:Male; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000378:metabolism
D011976:Receptors, Muscarinic; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases