HOW DOES INSULIN AFFECT CYTOSOLIC CALCIUM IN VASCULAR SMOOTH-MUSCLE CELL

To evaluate the effect of insulin on the calcium homeostasis in vascul ar smooth muscle cells (VSMC) the cytosolic free calcium concentration ([Ca2+]i) was measured in VSMC from spontaneously hypertensive rats f rom the Munster strain (SHR) and normotensive Wistar-Kyoto rats (WKY) using the fluorescent dye technique. Insulin increased [Ca2+]i in VSMC in a dose-dependent manner. At a concentration of 10(-5) U/ml the ins ulin induced [Ca2+]i increase was 107 +/- 25 nmol/l (mean +/- SEM) in VSMC from SHR and 82 +/- 27 nmol/l in VSMC from WKY. The stimulation o f protein kinase C by 100 nmol/l phorbol-12-myristate-13-acetate enhan ced the insulin-induced [Ca2+]i increase in VSMC to 224 +/- 58 nmol/l (p <0.01 compared to control). The inhibition of Na+/K+-ATPase by 1 mM ol/l ouabain enhanced the insulin induced (Ca2+]i increase in VSMC to 232 +/- 55, nmol/l (p <0.01 compared to control). On the other hand, t he inhibition of protein kinase C by isoquinoline-sulphonyl-O-2-methyl piperazine (H-7, 43 +/- 20 nmol/l) or addition of nifedipine (34 +/- 2 5 nmol/l) reduced the insulin induced (Ca2+]i increase. In summary, ph ysiologic concentrations of insulin can induce transplasmamembrane cal cium influx and may thereby affect the tone of vascular resistance ves sels.