EFFECT OF DIABETES ON CYTOSOLIC FREE CA2+ AND NA+-K+-ATPASE IN RAT AORTA

We examined Na+-K+-ATPase activity and the levels of alpha-I-, alpha-II-, and beta-subunit mRNA and protein in aortic cells of diabetic rats. Diabetes was induced by streptozocin. Na+-K+-ATPase activity was significantly reduced on the 2nd day of diabetes (9.4 +/- 1.3 vs. 17.5 +/- 2.1-mu-mol NADH . mg-1 protein . h-1, P < 0.05) and remained depressed on days 7 and 14. The levels of 5.3-kilobase (kb) mRNA band of the catalytic alpha-II-subunit of Na+-K+-ATPase were also decreased on the 2nd day of diabetes, whereas the second band, 3.4 kb, was not affected. Both bands were significantly decreased on days 7 and 14. This was followed by a reduction in the levels of alpha-II-protein (day 14). The levels of alpha-I- and beta-subunit mRNA and alpha-I- protein were not affected by diabetes. A decrease in Na+-K+-ATPase activity was accompanied by a significant (P < 0.001) increase in the cytosolic free Ca2+ concentrations ([Ca2+]i) in diabetic aortic cells (221 +/- 18 nM on the 7th day and 242 +/- 17 nM on the 14th day vs. 153 +/- 7 nM in controls). These findings are consistent with the hypothesis that decreased Na+-K+-ATPase activity and gene expression in vascular smooth muscle cells with accompanied rises in [Ca2+]i may be an important pathogenetic factor in the development of hypertension and atherosclerosis in diabetes.