The effect of phosphoglycerides on the incorporation of cholesterol into isolated brush-border membranes from rabbit small intestine.

The incorporation of cholesterol from bile salt micelles into brush-border membranes was found to be similar whether these originated from jejunum, ileum or whole small intestine. This incorporation, however, was appreciably lower in membranes obtained from duodenum. Studies pursued with membranes from whole small intestine revealed that dipalmitoyl or dioleoylphosphatidylcholine, when micellized together with the sterol and taurocholate markedly inhibited the incorporation. The didecanoyl and dilauroyl analogues of this lipid class were without significant effect. Preincubation of the membranes for 30 min at 37 degrees C with or without dipalmitoylphosphatidylcholine had no effect on cholesterol incorporation. Again in this case, suppression of sterol uptake could be seen only when phosphatidylcholine was admixed with the sterol. In contrast, dipalmitoyl and dilauroylphosphatidylethanolamines were found to be stimulatory rather than inhibitory. Addition of palmitic acid to the sterol-bile salt micelles had no effect on the uptake of cholesterol; however, this fatty acid could completely reverse the inhibition of cholesterol uptake by dipalmitoylphosphatidylcholine. The present study supports the conclusion that cholesterol incorporation into isolated brush-border membranes is governed largely by factors which affect the partitioning of the sterol out of the bile salt micelle.