Determination of Ca2+-atpase activity in streptozotocin-induced diabetic rat liver

Microsomal Ca2+-ATPase activity was studied in control and streptozotocin (STZ)-induced diabetic rat livers. Male rats were rendered diabetic by injection of STZ (45 mg/kg body weight) via the tail vein. Diabetic rats at 1, 4, 8, 10 or 15 wk and control rats were sacrificed. Liver tissues were obtained for the isolation of Ca2+-ATPase. Ca2+-ATPase activity was determined spectrophotometrically and lipid peroxidation [measured as tiobarbituric acid reactive substances (TBARS)] in liver tissues was determined spectrofluorometrically. Total calcium was measured by atomic absorption spectrophotometry. Blood glucose levels of the diabetic animals were >500 mg/dl at 4, 8, 10 and 15 wk of diabetes. Ca2+-ATPase activity was significantly decreased at all weeks of diabetes compared to control group (p<0.001). Ca2+-ATPase activity of control rats was 0.193 +/- 0.015 U/I whereas activity was 0.130 +/- 0.015 U/I at 15 wk of diabetes. The difference in calcium levels of diabetic rat livers was not significantly different compared to control group. On the other hand TBARS were elevated by 67% at 15 wk of diabetes. The decrease in enzyme activity may have been caused by elevated TBARS levels observed in liver tissue sindicative of increased lipid peroxidation.