LATERAL DIFFUSION AND FATTY-ACID COMPOSITION IN VASCULAR SMOOTH-MUSCLE MEMBRANE FROM STROKE-PRONE SPONTANEOUSLY HYPERTENSIVE RATS

We measured membrane fluidity and fatty acid composition in cultured v ascular smooth muscle cells from stroke-prone spontaneously hypertensi ve and Wistar-Kyoto normotensive rats. Membrane fluidity was measured as a lateral diffusion of 5 N (octadecanoyl) aminofluorescein using fl uorescence microscopy and fluorescence recovery after photobleaching. Fatty acid composition of membrane fractions was measured using high p erformance liquid chromatography. Lateral diffusion was significantly lower (the membrane had lower fluidity) in vascular smooth muscle cell s from stroke-prone spontaneously hypertensive rats as compared to tho se cells isolated from Wistar-Kyoto reference strain. The ratio of ara chidonic acid to total fatty acids was 0.058+/-0.007 in the plasma mem brane from stroke-prone spontaneously hypertensive rats and 0.036+/-0. 005 in that from Wistar-Kyoto rats, P=.005. Similarly, the ratios of a rachidonic to oleic acid and arachidonic to palmitic acid were signifi cantly greater in cells from stroke-prone spontaneously hypertensive r ats (P=.002 for difference in each ratio).These results show decreased lateral diffusion (decreased membrane fluidity) in vascular smooth mu scle cells from stroke-prone spontaneously hypertensive rats. This is associated with increased content of arachidonic acid, the major precu rsor of prostaglandins and other eicosanoids. We postulate that local changes in the unsaturated fatty acid composition related to arachidon ic acid storage and release contribute to reduced membrane fluidity in stroke-prone spontaneously hypertensive rats.