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

The effects of dietary (n-6)/(n-3) polyunsaturated fatty acid balance on fa tty acid composition, ouabain inhibition, and Na+ dependence of Na+, K+-ATP ase isoenzymes of whole brain membranes were studied in 60-day-old rats fed over two generations a diet either devoid of alpha-linolenic acid [18:3(n- 3)] (sunflower oil diet) or rich in 18:3(n-3) (soybean oil diet). In the br ain membranes, the sunflower oil diet led to a dramatic decrease in docosah exaenoic acid [22:6(n-3)] membrane content. The activities of Na+, K+-ATPas e isoenzymes were discriminated on the basis of their differential affiniti es for ouabain and their sensitivity to sodium concentration The ouabain ti tration curve of Na+,K+-ATPase activity displayed three inhibitory processe s with markedly different affinity [i.e., low (alpha 1), high (alpha 2), an d very high (alpha 3)] for brain membranes of rats fed the sunflower oil di et, whereas the brain membranes of rats fed the soybean oil diet exhibited only two inhibitory processes, low (alpha 1) and high (alpha 2' = alpha 2 alpha 3). Regardless of the diet, on the basis of the Na+ dependence of Na +, K+-ATPase activity, three isoenzymes were Sound: alpha 1 form displaying an affinity 1.5- to 2-fold higher that of than alpha 2 and 3-fold higher t hat of alpha 3. In vats fed the sunflower oil diet, alpha 2 isoenzyme exhib ited 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 membra ne lipid environment modulates the functional properties of Na+, K+-ATPase isoenzymes of high ouabain affinity (alpha 2). (C) Elsevier Science Inc. 19 99. All rights reserved.