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

Abstract

The activity of (Ca 2-+ Mg 2 +)-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+ + Mf+)-ATPase observed previously in kidney membranes of the diabetic rats.

Abnormal Ca2+-ATPase Activity in Erythrocytes of Non-Insulin-Dependent Diabetic Rats

“…It is, in turn, the immediate phospholipid milieu surrounding the Ca 2 + -ATPase molecule that exerts the greatest influence on the enzyme activity ( Warren, Houslay, Metcalfe and Birdsall 1975). Accordingly, abnormal membrane phospholipid content and distribution as seen also in diabetic patients (Levy et al 1988;Wali, Jaffe, Kumar and Kalra 1988;Kalofoutis and Lekakis 1981) could explain the abnormal Ca + -ATPase ac-tivity in membranes from diabetic animals and humans. Whether a different pattern of changes in phospholipid composition in the NIDD and IDD condition can explain the differences in Ca2 + -ATPase activity in the two conditions remains to be determined.…”

Effects of vitamin E on microsomal Ca2+‐ATPase activity and calcium levels in streptozotocin‐induced diabetic rat kidney

“…28 Workers have found that the phosphatidylinositol content of the kidney increases in diabetic rats. 29 The increase in the acidic phospholipid content of membranes has been suggested to be an important factor resulting in increased Ca 2þ -ATPase activity in diabetic animals. 15,28 In addition to regulation by acidic phospholipids, polyunsaturated fatty acids, protein kinases A 30 and C, 31 cyclic GMP-dependent protein kinase (G-kinase) 32 can also activate the enzyme.…”

Metabolism of exogenous S-adenosylmethionine in isolated rat hepatocyte suspensions: methylation of plasma-membrane phospholipids without intracellular uptake

“…Since rat liver has 2 mg of plasma membrane protein per g wet weight [32], containing approx. 100 nmol of phosphatidylethanolamine per mg of protein [33,34], one can calculate that these membranes contain approx. 200 nmol of phosphatidylethanolamine per g wet weight of hepatocytes.…”