Ca(2+)-ATPase activity in streptozotocin-induced diabetic rat kidneys

Kidney Ca(2+)-ATPase activity was altered in streptozotocin (STZ)-induced diabetic rats. Male rats, 200-250 g, were rendered diabetic by injection of STZ 45 mg/kg body weight via the tail vein. Following injection, control rats and diabetic rats at 1, 4, 8 or 15 weeks were sacrificed. Kidney tissues were obtained for the isolation of Ca(2+)-ATPase. Ca(2+)-ATPase activity was determined spectrophotometrically. Total calcium was measured by atomic absorption spectrophotometry. Diabetic rats had significantly elevated blood glucose levels compared to controls. Blood glucose levels were 92.92 +/- 1.215 mg/dl (mean +/- S.E.M.) for the control group, and 362.50 +/- 9.613 mg/dl at one week and > 500 mg/dl at 4, 8 and 15 weeks of diabetes. Enzyme activities were significantly higher at 4, 8 and 15 weeks of diabetes than in the control group (p < 0.001). There was no significant increase at one week of diabetes. Ca(2+)-ATPase activity was 0.43 +/- 0.003 U/L, 0.517 +/- 0.058 U/L, 0.707 +/- 0.078 U/L, 0.730 +/- 0.006 U/L and 0.715 +/- 0.055 U/L respectively for controls and rats at 1, 4, 8 and 15 weeks of diabetes. Calcium levels in diabetic rat kidneys were also significantly higher than for controls. The increase in enzyme activity may have been caused by higher calcium levels in diabetic kidneys resulting from a compensatory response of the enzyme to high levels of the ion.