Ca2+-Mg2+-ATPase activity in kidney basolateral membrane in non-insulin-dependent diabetic rats. Effect of insulin.
The direct effect of insulin on the high-affinity Ca2+-Mg2+-ATPase was studied in kidney proximal tubular basolateral membranes (BLM) obtained from control and streptozocin-induced non-insulin-dependent diabetes mellitus (NIDDM) rats. Plasma glucose of the diabetic animals was only mildly elevated (217 +/- 9 vs. 138 +/- 3 mg/dl). Both high- and low-affinity calcium-dependent Ca2+-Mg2+-ATPase activities were identified in the BLM. Enzyme activity in BLM from diabetic rats was higher at all Ca2+ concentrations tested due to a higher maximum velocity of the enzyme from NIDDM rats. The high-affinity Ca2+-Mg2+-ATPase activity was inhibited by trifluoroperazine (TFP) in both membranes. No difference in calmodulin content was found in the membranes from the diabetic and control rats. Insulin (16-200 microU/ml) significantly increased the high-affinity Ca2+-Mg2+-ATPase activity (17-40%) in membranes from control animals but had no effect on the enzyme activity in the membranes from the NIDDM rats. The basal activity of the enzyme at 0.1 microM free Ca2+ was higher in the BLM from the NIDDM animals compared to controls (17.8 +/- 0.5 vs. 14.7 +/- 0.8 nM Pi X mg-1 X min-1; P less than .02). There was no effect of insulin on the Ca2+-independent ATPase activity of BLM preparations. These findings demonstrate a defect in the ability of insulin to regulate the high-affinity Ca2+-Mg2+-ATPase activity in BLM from diabetic rats. Such a defect in enzyme activity may play a role in the mechanism of impaired insulin action observed in these NIDDM rats.
D000818:Animals; D001485:Basement Membrane / Q000201:enzymology; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology; D007328:Insulin / Q000494:pharmacology*; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D051381:Rats; D011919:Rats, Inbred Strains; D014268:Trifluoperazine / Q000494:pharmacology
D007328:Insulin; D014268:Trifluoperazine; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium