Cholesterol biosynthesis and modulation of membrane cholesterol and lipid dynamics in rat intestinal microvillus membranes.

Experiments were performed to test the hypothesis that cholesterol biosynthesis in the rat ileal enterocyte, the major absorptive cell lining the distal epithelium of the small intestine, can modulate the cholesterol content and the motional freedom of the plasma membrane lipids. Decreased sterol biosynthesis in vivo was elicited by feeding sodium taurocholate or by fasting the rats, whereas increased synthesis was induced by biliary ligation or feeding cholestyramine, a bile salt binding resin; these effects were monitored by assay of mucosal 3-hydroxy-3-methylglutaryl coenzyme A reductase. After each procedure, isolated microvillus membranes were examined to determine the lipid composition and the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene. The results demonstrate that variations in cholesterol biosynthesis in vivo can modulate the cholesterol content and the motional freedom of the lipids of the microvillus membrane; similar effects were not observed on the basolateral membrane. The observations suggest that the normal pattern of decreased lipid motional freedom in microvillus membranes of the distal as compared to the proximal small intestine of the rat results from higher rates of cholesterol biosynthesis in the distal mucosa.