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 dy namic properties of the lipid matrix of rat liver microsomes and eryth rocyte membranes was studied. The rate and range of the rotational mob ility of 1,6-diphenyl-1,3,5-hexatriene and 2-, 7-, and 12-(9-anthroylo xy)stearate probes in the native membranes and in lipid vesicles prepa red with the total lipid extracts of these membranes were evaluated by using differential polarized phase fluorometry. For the anthroyloxyst earate probes, two modes of rotation (in and out of the plane of the a romatic anthracene ring) were partially resolved by measuring at diffe rent excitation wavelengths. The fat-free diet produces important chan ges 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 glyceropho spholipid class distribution. The principal changes, more pronounced i n liver microsomes than in erythrocytes, are: an increase in nonessent ial monoene and triene (18:1n-9 and 20:3n-9) and a decrease in essenti al diene (18:2n-6) and tetraene (20:4n-6). These changes modify the do uble-bond distribution as a function of the distance from the interpha se toward the bilayer interior, with a significant deficit (15% in ery throcytes and 30% in liver microsomes) in the double-bond density in t he intermediate region of the membrane leaflet, corresponding to the c arbon number 11-12 of an extended saturated acyl chain, and where the 12-anthroyloxystearate probe is located. In spite of the changes in fa tty acid composition and double-bond distribution, with the only excep tion of a slight increase (about 15%) in the ''out of the plane'' rota tion rate of the 7-(9-anthroyloxy) stearate probe in the erythrocyte l ipid vesicles, no other significant change is observed. jlr 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 lipi d phase of the membrane, sensed by these probes, would be almost exact ly compensated.