Membrane fluidity and fatty acid metabolism in kidney cells from rats fed purified eicosapentaenoic acid or purified docosahexaenoic acid.

Rats were given a supplement (1.5 ml/day) of purified eicosapentaenoic acid (EPA, 20:5,n-3), purified docosahexaenoic acid (DHA, 22:6,n-3)), or corn oil for 10 days. Membrane fluidity, measured as the steady-state fluorescence polarization of diphenylhexatriene (DPH), was approximately 20% lower in kidney cells from rats fed purified EPA than in cells from the DHA-fed or corn-oil fed animals. The level of 20:5(n-3) in kidney phospholipids was 18 times higher in rats fed EPA, and four times higher in those fed DHA as compared to the corn-oil group. The level of arachidonic acid (20:4,n-6) was concomitantly decreased, while linoleic acid (18:2,n-6) was increased in kidney-phospholipids in the n-3 fatty acid fed rats. The proportion of 22:6(n-3) in kidney phospholipids was not affected by EPA supplementation, while the DHA diet slightly increased the level of this fatty acid. The distribution of phospholipid subclasses was significantly altered in that phosphatidylcholine was increased and phosphatidylethanolamine was concomitantly decreased. It is suggested that the decrease in 20:4(n-6) is relatively more important in the regulation of fluidity than a concomitant increase in 20:5(n-3). It is also suggested that the compensatory modifications of the phospholipid subclass distribution as a response to decreased 20:4(n-6)/20:5(n-3) ratio was not sufficient to maintain fluidity when the ratio was as low as in the present study. The incorporation of labelled linolenic acid (18:3,n-3) in phospholipids was decreased in cells from the n-3 supplemented rats. Since endogenous 22:5(n-3) in phospholipids was only increased in the EPA group, 22:6(n-3) only in the DHA group, and 20:5(n-3) in both, it is suggested that the decreased incorporation of labelled 18:3(n-3) into phospholipids of the DHA-fed rats in particular is correlated to the increased level of 22:6(n-3) in the membrane phospholipids. The incorporation of fatty acids into phopholipids may thus show substrate specificity, in that 22:6(n-3) is less exchangable with labelled 18:3(n-3) than is 20:5(n-3). These results demonstrate that increasing levels of n-3 fatty acids in membranes affect the uptake and intracellular metabolism of fatty acids as well as membrane fluidity in the kidney.