The uptake of phosphatidylcholine by brush-border membranes isolated from rabbit small intestine

The uptake of [H3] dipalmitoyl phosphatidylcholine by isolated brush border membranes from rabbit small intestine was studied. The process was found to be stimulated by Ca2+ in a manner which was influenced by the protein -Ca2+ concentration ratio. At higher ratios the enhancement by divalent cation was diminished. Preincubation of the membranes with Ca2+ followed by their transfer to a Ca2+-free medium did not result in enhancement of uptake. The stimulation by Ca2+ could be seen only when this cation was present in the incubation medium. The uptakes of [1-14C] palmitic acid, and di-[1-14C] palmitoylglycerol were also examined and found to be comparable in extent to that of labelled phosphatidylcholine but more pronounced than that of 2-[1-14C] palmitoylglycerol. The incorporation of labelled palmitic acid, phosphatidylcholine or monoglyceride in brush border membranes prepared from jejunum and ileum was similar. The results indicate that brush border membranes are capable of incorporating a variety of exogenous lipids especially in the presence of Ca2+ and the possible consequences of such uptake on the structure and function of the membrane are discussed.