Lipid Composition and Fluidity in the Jejunal Brush-Border Membrane of Spontaneously Hypertensive Rats. Effects on Activities of Membrane- Bound Proteins

Abstract

The lipid compositíon and fluidity of jejunal brush-border membrane vesicles (BBMV) have been studied in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats. The activities of both Na+-dependent D-glucose cotransport and Na+-H antiport have also been determined. A significan! increase in the level of free cholesterol was observed in jejunal BBMV from SHR compared to WKY rats. Since phospholipid values did not change in either group of animals, a significan! enhancement in the free cholesterol/phospholipid ratio was observed in SHR. A decrease in the levels of phosphatidylethanolamine together with an increase in the values of phos­ phatidylserine was observed in hypertensive rats. Although the content of phosphatidylcholine (PC) and sphingomyelin (SM) was not singificantly altered in SHR, the ratio PC/SM significantly increased in these animals when compared to WKY rats. The majar fatty acids present in bursh-border membranes prepared from SHR and WKY rats were palmitic (16:0), stearic (18:0), oleic (18:1, n-9) and linoleic (18:2, n-6), and the fatty acid composition was not modified by the hypertension. A decreased fluorescence polarization, i.e., increased membrane ftuidity, was observed in SHR, which was not correlated to the increased ratio of cholesterol/phospholipid found in the brush-border membrane isolated from these animals. These structural changes found in SHR were associated to an enhancement in both Na+ -dependent D-glucose transport and Na+-H+ antiport activíty in the jejunal BBMVof SHR.