Effects of docosahexaenoic acid on annular lipid fluidity of the rat bile canalicular plasma membrane

The role of docosahexaenoic acid (DHA) in the fluidity of the annular lipid regions and their associated membrane-bound proteins is still not as well understood as that in the global (bulk) lipid regions. We therefore studied the effects of dietary DHA on the relationship between annular and global lipid fluidity and membrane-bound enzymes such as 5 ' -nucleotidase and Mg2 +-ATPase in the rat bile canalicular membrane. Dietary DHA caused significa nt increases in 5 ' -nucleotidase and Mg2+-ATPase activity and in global an d annular lipid fluidity, a higher increase in fluidity in the annular lip ids than the global lipids, and a decrease in the cholesterol-to-phospholip id molar ratio in the canalicular membrane, Plasma total cholesterol and LD L cholesterol decreased, and fecal cholesterol increased in the DHA-fed rat s, No changes were observed in oxidative markers, but glutathione peroxidas e increased in the liver with DHA feeding, Annular lipid fluidity, but not global lipid fluidity, correlated remarkably well with DHA synchronously wi th the activities of 5 ' -nucleotidase and Mg2+-ATPase. The data indicate t hat the DHA-induced increase in annular lipid fluidity is responsible for t he increases observed in the enzyme activity.jlr We therefore concluded tha t the increased activity of membrane-bound enzymes and transporters induced by DHA and the concomitant increase in annular lipid fluidity comprise one of the mechanisms involved in DHA-induced clearance of plasma cholesterol.