Interaction of lipids with intestinal brush border membrane preparations

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Abstract
Conditions for uptake of lipids by rabbit intestinal brush border membrane preparations were investigated. A variety of lipids were incorporated, including choline and ethanolamine phosphatides, as well as cholesterol, diglyceride and fatty acid. The incorporation of those lipids tested was enhanced by Ca2+ and other divalent cations, but not by monovalent cations. The optimal Ca2+ concentration was .apprx. 10 mM. The uptake varied with lipid and membrane protein concentration and proceeded at rates which were too rapid to measure under several assay conditions tried. Incorporations were decreased substantially outside the pH range of 6.5-8.0. The effect of 1 lipid, phosphatidylcholine, on the structural appearance of the membrane fraction was examined by EM. No free or surface-bound lipid structures could be detected, and the membrane fractions appeared to be unchanged after uptake.