Characterization and Localization of Calcium/Phospholipid-Dependent Protein Kinase-C during Diabetic Renal Growth

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Abstract
The substrate specificities of calcium/phospholipid-dependent kinase-C (PKC) were examined in rat kidney cortex, and localization of the protein was studied after the induction of diabetes. The cytosolic kinase was eluted from an anion exchange resin using a linear gradient of 0-0.15 M NaCl. A sharp peak of activity was demonstrated at approximately 80 mM using histone as a substrate. The kinase demonstrated a broad pH optimum of 6.5-8.0. ATP was the preferred phosphorus donor. The Ka for ATP averaged 2.6 .+-. 0.1 .mu.M (n = 4 ) and was not different in diabetic animals. Lysine-rich histones, but not arginine-rich or mixed histones, were the most suitable phosphorus acceptors. Phosphatidylserine stimulated kinase activity with Ka of 4.5 .+-. 0.7 .mu.M in the presence of 20 .mu.M diolein (n = 3). Twenty micromolar diolein in the presence of 25 .mu.M phosphatidylserine lowered the apparent Ka for calcium from 17.2 .+-. 1.4 to 3.3 .+-. 1.5 .mu.M (n = 3; P < 0.01). Similar data were evident in diabetic animals. Diabetic renal growth was induced by the injection of streptozotocin (35 mg/kg, i.v). At the end of 4 weeks, blood glucose averaged 119.6 .+-. 7.4 mg/dl in vehicle-injected controls and 548.7 .+-. 21.6 mg/dl in diabetic animals (n = 5; P < 0.001). Despite reduced weight gains in diabetic animals, renal protein content was increased in this group compared to the control value. Neither cytosolic nor proximal tubule basolateral membrane PKC activity changed after the induction of diabetes; however, luminal brush border PKC activity increased from 83.8 .+-. 4.6 pmol/mg .cntdot. min in control animals to 107.3 .+-. 5.5 pmol/mg .cntdot. min in diabetic animals (n = 5; P < 0.02). The increased activity in the brush border membrane may have important consequences for the growth response of the kidney in diabetes.