MODULATION OF THE L-TYPE CA-CHANNELS BY INSULIN-TREATMENT IN RAT AORTA

Intracellular Ca2+ is a major regulator of vascular smooth muscle forc e generation. Because of this important role, the concentration of Ca2 + within the cell is tightly regulated by means of sequestration and e xtrusion transport processes. Insulin was found to increase the plasma lemma Ca-ATPase expression. In this work we have found that the expres sion of the L-type calcium channels, which are known to play an import ant role in the regulation of vasoconstriction and vasodilatation, is affected by insulin. We have found that single injection of insulin se lectively decreased the Ca-channel expression in 150 min. Passive Ca-t ransport into proteoliposomes of plasma membrane proteins from the rat aorta was also decreased in 150 min, while after a longer resting per iod the Ca-transport was comparable to that from the control group. Wh en insulin was added in vitro directly to a reaction mixture, an incre ase in the Ca-transport was found. No changes in Na/K-ATPase, which fu nctions as cotransport system with Na/Ca exchanger, were observed. On the contrary, seven insulin injections and a subsequent 2.5 hour rest did not cause changes in the Ca channel expression. In the animals tre ated seven times with insulin, the decrease in the Ca-transport was de layed compared to single insulin injection. Our results suggest that i nsulin affects L-type calcium channels in the rat aorta by a decrease in the Ca-channel expression.