Effect of alterations in membrane lipid unsaturation on the properties of the insulin receptor of Ehrlich ascites cells

Abstract

We have altered the phospholipid composition of the plasma membranes of Ehrlich ascites cells grown in mice and studied the effects on the properties of the insulin receptor of this cell. The insulin receptor of the Ehrlich cell demonstrated all of the binding characteristics of mammalian insulin receptors: specificity for insulin and insulin analogs, saturability, inverse relationship of steady-state binding levels to temperature, and negative cooperativity. Cellular phospholipids enriched in monounsaturated fatty acyl groups were produced by growth in animals that were maintained on a diet rich in coconut oil; cellular phospholipids enriched in polyunsaturated fatty acyl groups were produced in animals fed sunflower oil. Insulin receptors were present in the normal cells at 180 000 sites/cell but this fell to 125 000 ( p <0.001) in cells enriched in monounsaturated fatty acids and rose to 386 000 ( p <0.001) in cells enriched in polyunsaturated fatty acids. The normal cells had affinity constants ( K e and K f ) of 0.03 and 0.01 nM −1. The cells enriched in monounsaturated fatty acids had an increase in these affinity constants to 0.06 and 0.03 nM −1 whereas values of 0.01 and 0.005 nM −1 were obtained in the cells enriched in polyunsaturated fatty acids (all comparison p <0.001). Thus, increased unsaturation of plasma membrane phospholipids, produced by dietary manipulations, was associated with an increase in insulin receptor number but a decrease in binding affinity. In contrast, increased saturation of the phospholipids of the plasma membrane was associated with a decrease in receptor number and an increase in affinity. The results can be explained by a model in which the insulin receptor is assumed to be multimeric.