inositol-1-4-5-trisphosphate and Diabetic-Angiopathies

This study examines the extent to which the antiapoptotic Bcl-2 proteins Bcl-2 and Bcl-x(L) contribute to diabetic Ca(2+) dysregulation and vessel contractility in vascular smooth muscle cells (VSMCs) through their interaction with inositol 1,4,5-trisphosphate receptor (InsP(3)R) intracellular Ca(2+) release channels. Measurements of intracellular ([Ca(2+)](i)) and sarcoplasmic reticulum ([Ca(2+)](SR)) calcium concentrations were made in primary cells isolated from diabetic (db/db) and nondiabetic (db/m) mice. In addition, [Ca(2+)](i) and constriction were recorded simultaneously in isolated intact arteries. Protein expression levels of Bcl-x(L) but not Bcl-2 were elevated in VSMCs isolated from db/db compared with db/m age-matched controls. In single cells, InsP(3)-evoked [Ca(2+)](i) signaling was enhanced in VSMCs from db/db mice compared with db/m. This was attributed to alterations in the intrinsic properties of the InsP(3)R itself because there were no differences between db/db and db/m in the steady-state [Ca(2+)](SR) or InsP(3)R expression levels. Moreover, in permeabilized cells the rate of InsP(3)R-dependent SR Ca(2+) release was increased in db/db compared with db/m VSMCs. The enhanced InsP(3)-dependent SR Ca(2+) release was attenuated by the Bcl-2 protein inhibitor ABT-737 only in diabetic cells. Application of ABT-737 similarly attenuated enhanced agonist-induced [Ca(2+)](i) signaling only in intact aortic and mesenteric db/db vessels. In contrast, ABT-737 had no effect on agonist-evoked contractility in either db/db or db/m vessels. Taken together, the data suggest that in type 2 diabetes the mechanism for [Ca(2+)](i) dysregulation in VSMCs involves Bcl-2 protein-dependent increases in InsP(3)R excitability and that dysregulated [Ca(2+)](i) signaling does not appear to contribute to increased vessel reactivity.

Topics: Animals; Aorta, Thoracic; bcl-X Protein; Biphenyl Compounds; Blood Glucose; Calcium; Calcium Signaling; Cells, Cultured; Diabetes Mellitus, Type 2; Diabetic Angiopathies; Disease Models, Animal; Dose-Response Relationship, Drug; Homeostasis; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptors; Male; Mice; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Nitrophenols; Piperazines; Proto-Oncogene Proteins c-bcl-2; Sarcoplasmic Reticulum; Sulfonamides; Time Factors; Up-Regulation; Vasoconstriction

The effects of exogenous phosphatidic acid (PA) on Ca2+ transients and contractile activity were studied in cardiomyocytes isolated from chronic streptozotocin-induced diabetic rats. In control cells, 25 microM PA induced a significant increase in active cell shortening and Ca2+ transients. PA increased IP3 generation in the control cardiomyocytes and its inotropic effects were blocked by a phospholipase C inhibitor. In cardiomyocytes from diabetic rats, PA induced a 25% decrease in active cell shortening and no significant effect on Ca2+ transients. Basal and PA-induced IP3 generation in diabetic rat cardiomyocytes was 3-fold lower as compared to control cells. Sarcolemmal membrane PLC activity was impaired. Insulin treatment of the diabetic animals resulted in a partial recovery of PA responses. Our results, therefore, identify an important defect in the PA-PLC signaling pathway in diabetic rat cardiomyocytes, which may have significant implications for heart dysfunction during diabetes.

Topics: Animals; Calcium; Cardiomyopathies; Cells, Cultured; Diabetes Mellitus, Experimental; Diabetic Angiopathies; Inositol 1,4,5-Trisphosphate; Isoenzymes; Kinetics; Male; Myocardial Contraction; Myocytes, Cardiac; Phosphatidic Acids; Phospholipase C delta; Rats; Rats, Sprague-Dawley; Signal Transduction; Type C Phospholipases

Phospholipase C (PLC) activity is known to influence cardiac function. This study was undertaken to examine the status of PLC beta3 in the cardiac cell plasma membrane (sarcolemma, SL) in an experimental model of chronic diabetes. SL membrane was isolated from diabetic rat hearts at 8 weeks after a single i.v. injection of streptozotocin (65 mg/kg body weight). The total SL PLC was decreased in diabetes and was associated with a decrease in SL PLC beta3 activity, which immunofluorescence in frozen diabetic left ventricular tissue sections revealed to be due to a decrease in PLC beta3 protein abundance. In contrast, the SL abundance of Gqalpha was significantly increased during diabetes. These changes were associated with a loss of contractile function (+/- dP/dt). A 2-week insulin treatment of 6-week diabetic animals partially normalized all of these parameters. These findings suggest a defect in PLC beta3-mediated signaling processes may contribute to the cardiac dysfunction seen during diabetes.

Topics: Animals; Cardiomyopathies; Diabetes Mellitus, Experimental; Diabetic Angiopathies; GTP-Binding Protein alpha Subunits, Gq-G11; Heart Ventricles; Inositol 1,4,5-Trisphosphate; Insulin; Isoenzymes; Male; Myocytes, Cardiac; Phospholipase C beta; Rats; Sarcolemma; Type C Phospholipases