Diet deficient in alpha-linolenic acid alters fatty acid composition and enzymatic properties of Na +, K +-ATPase isoenzymes of brain membranes in the adult rat

Abstract

The effects of dietary (n-6)/(n-3) polyunsaturated fatty acid balance on fatty acid composition, ouabain inhibition, and Na + dependence of Na +, K +-ATPase isoenzymes of whole brain membranes were studied in 60-day-old rats fed over two generations a diet either devoid of α-linolenic acid [18:3(n-3)] (sunflower oil diet) or rich in 18:3(n-3) (soybean oil diet). In the brain membranes, the sunflower oil diet led to a dramatic decrease in docosahexaenoic acid [22:6(n-3)] membrane content. The activities of Na +, K +-ATPase isoenzymes were discriminated on the basis of their differential affinities for ouabain and their sensitivity to sodium concentration. The ouabain titration curve of Na +, K +-ATPase activity displayed three inhibitory processes with markedly different affinity [i.e., low (α1), high (α2), and very high (α3)] for brain membranes of rats fed the sunflower oil diet, whereas the brain membranes of rats fed the soybean oil diet exhibited only two inhibitory processes, low (α1) and high (α2′ = α2 + α3). Regardless of the diet, on the basis of the Na + dependence of Na +, K +-ATPase activity, three isoenzymes were found: α1 form displaying an affinity 1.5- to 2-fold higher that of than α2 and 3-fold higher that of α3. In rats fed the sunflower oil diet, α2 isoenzyme exhibited higher affinity for sodium (Ka = 8.8 mmol/L) than that of rats fed the soybean oil diet (Ka = 11.7 mmol/L). These results suggest that the membrane lipid environment modulates the functional properties of Na +, K +-ATPase isoenzymes of high ouabain affinity (α2).