Calcium homeostasis in vascular smooth muscle cells is altered in type 2 diabetes by Bcl-2 protein modulation of InsP3R calcium release channels

Abstract

This study examines the extent to which the antiapoptotic Bcl-2 proteins Bcl-2 and Bcl-xLcontribute to diabetic Ca2+dysregulation and vessel contractility in vascular smooth muscle cells (VSMCs) through their interaction with inositol 1,4,5-trisphosphate receptor (InsP3R) intracellular Ca2+release channels. Measurements of intracellular ([Ca2+]i) and sarcoplasmic reticulum ([Ca2+]SR) calcium concentrations were made in primary cells isolated from diabetic ( db/db) and nondiabetic ( db/m) mice. In addition, [Ca2+]iand constriction were recorded simultaneously in isolated intact arteries. Protein expression levels of Bcl-xLbut not Bcl-2 were elevated in VSMCs isolated from db/db compared with db/m age-matched controls. In single cells, InsP3-evoked [Ca2+]isignaling was enhanced in VSMCs from db/db mice compared with db/m. This was attributed to alterations in the intrinsic properties of the InsP3R itself because there were no differences between db/db and db/m in the steady-state [Ca2+]SRor InsP3R expression levels. Moreover, in permeabilized cells the rate of InsP3R-dependent SR Ca2+release was increased in db/db compared with db/m VSMCs. The enhanced InsP3-dependent SR Ca2+release was attenuated by the Bcl-2 protein inhibitor ABT-737 only in diabetic cells. Application of ABT-737 similarly attenuated enhanced agonist-induced [Ca2+]isignaling 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 [Ca2+]idysregulation in VSMCs involves Bcl-2 protein-dependent increases in InsP3R excitability and that dysregulated [Ca2+]isignaling does not appear to contribute to increased vessel reactivity.