ALTERATIONS IN THE PHYSICAL STATE AND COMPOSITION OF BRUSH-BORDER MEMBRANE-LIPIDS OF RAT ENTEROCYTES DURING DIFFERENTIATION

The physical state of the membrane lipid of brush border membranes, prepared from rat small intestinal villus, and crypt cells, was examined by steady-state fluorescence polarization using 3 lipid-soluble fluorophors. Membranes prepared from crypt cells possess a higher lipid fluidity than those of villus cells with each probe. Analysis of the composition of these membranes revealed that those from crypt cells had lower ratios of cholesterol/phospholipid (mol/mol), protein/lipid (wt/wt), and saturated fatty acyl chains/unsaturated chains (wt/wt). Alterations in the levels of stearic (18:0) and oleic (18:1) acids were responsible for differences in the latter ratio. Alterations in the lipid composition and fluidity of brush border membranes of enterocytes occur during the process of differentiation.