Effect of fish oil diet on fatty acid composition of phospholipids of brain membranes and on kinetic properties of Na+,K(+)-ATPase isoenzymes of weaned and adult rats.

The influence of dietary (n-3) fatty acids (such as eicosapentaenoic and docosahexaenoic acids) as found in fish oil on Na+ sensitivity and ouabain affinity of Na+,K(+)-ATPase isoenzymes (alpha 1, alpha 2, alpha 3) was studied in whole brain membranes from weaned and adult rats fed diets for two generations. The long chain (n-3) fatty acids supplied by fish oil decreased the fatty acids of the (n-6) series compared with the standard diet, resulting in a decrease in the (n-6)/(n-3) molar ratio in both 21- and 60-day-old rats. On the basis of ouabain titration, three inhibitory processes with markedly different affinities were associated with isoenzymes, i.e., low affinity (alpha 1), high affinity (alpha 2), and very high affinity (alpha 3). It appears that the fish oil diet, in part via the modification of membrane fatty acid composition, altered the proportion and ouabain affinity of isoenzymes. Na+ sensitivity is the best criterion of physiologic change induced by fish oil diet. We calculated the Na+ activation for each isoenzyme and found one Na+ sensitivity and two Na+ sensitivities per isoenzyme in weanling and adult rats fed different diets, respectively. In contrast to alpha 2 and alpha 3, alpha 1 appears insensitive to membrane change induced by fish oil diet. Fish oil diet, which is known to confer cardioprotection, induced significant modulation of Na+,K(+)-ATPase isoenzymes at the brain level.