Plasma membrane phospholipid content in non-insulin-dependent streptozotocin-diabetic rats — effect of insulin

Summary The activity of (Ca²⁺ + Mg²⁺)-ATPase is impaired in kidney basolateral membranes from non-insulin-dependent streptozotocin-diabetic rats. To study the possible role of changes in membrane phospholipid content in the malfunction of this enzyme in kidney membranes of the diabetic animals, phospholipid (phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, and sphingomyelin) content was measured in kidney and liver membranes obtained from non-insulin-dependent diabetic rats. Total phospholipid content was similar in liver and kidney membranes of diabetic and control rats (595±47 versus 624±29 in liver and 469±22 versus 458±17 nmol Pi/mg protein in kidney respectively). Phosphatidylethanolamine content in kidney and liver membranes of diabetic rats was lower than in control rats (87.7±1.8 versus 96.4±2.2 nmol Pi/mg protein, p<0.01 and 87.1±3.7 versus 101.8±3.5, p<0.02 respectively). Phosphatidylinositol content was higher in kidney (28.0±0.6 versus 23.9±2.1, p<0.02) but not liver membranes from diabetic rats.The in vitro direct effect of insulin on the phospholipid content in kidney membranes was also measured. Physiologic concentrations of insulin (718 pmol/l for 30 min) increased the phosphatidic acid content in membranes from control but not from diabetic rats by 34.2% (p<0.02). This rise was readily measurable after 3 min of exposure to insulin. Insulin did not induce a significant change in the content of any other phospholipid in membranes from control or diabetic rats.These differences in phospholipid content demonstrated in isolated membranes obtained from non-insulin-dependent diabetic and control rats, before and after exposure to insulin, may explain, in part, the impaired function of the (Ca²⁺+Mg²⁺)-ATPase observed previously in kidney membranes of the diabetic rats.