Possible compensation of structural and viscotropic properties in hepatic microsomes and erythrocyte membranes of rats with essential fatty acid deficiency.

The effect of essential fatty acid deficiency on the structural and dynamic properties of the lipid matrix of rat liver microsomes and erythrocyte membranes was studied. The rate and range of the rotational mobility of 1,6-diphenyl-1,3,5-hexatriene and 2-, 7-, and 12-(9-anthroyloxy)stearate probes in the native membranes and in lipid vesicles prepared with the total lipid extracts of these membranes were evaluated by using differential polarized phase fluorometry. For the anthroyloxystearate probes, two modes of rotation (in and out of the plane of the aromatic anthracene ring) were partially resolved by measuring at different excitation wavelengths. The fat-free diet produces important changes in the fatty acid composition of the different glycerophospholipid classes without affecting the total double-bond number, the relative contents of cholesterol, phospholipid, and protein, and the glycerophospholipid class distribution. The principal changes, more pronounced in liver microsomes than in erythrocytes, are: an increase in nonessential monoene and triene (18:1n-9 and 20:3n-9) and a decrease in essential diene (18:2n-6) and tetraene (20:4n-6). These changes modify the double-bond distribution as a function of the distance from the interphase toward the bilayer interior, with a significant deficit (15% in erythrocytes and 30% in liver microsomes) in the double-bond density in the intermediate region of the membrane leaflet, corresponding to the carbon number 11-12 of an extended saturated acyl chain, and where the 12-anthroyloxystearate probe is located. In spite of the changes in fatty acid composition and double-bond distribution, with the only exception of a slight increase (about 15%) in the "out of the plane" rotation rate of the 7-(9-anthroyloxy)stearate probe in the erythrocyte lipid vesicles, no other significant change is observed. Thus, the changes in fatty acid composition would take place in such a way that at least the average structural and viscotropic properties of the lipid phase of the membrane, sensed by these probes, would be almost exactly compensated.