Ontogeny of basolateral membrane lipid composition and fluidity in small intestine

To evaluate physicochemical properties of the small intestinal basolateral cell surface during postnatal development, membranes were isolated from suckling (14-17 days) and weanling-mature (35-49 days) rabbit jejunal and ileal enterocytes at 30- to 40-fold purification (based on Na+-K+-ATPase specific activity) and with limited contamination from coisolated cellular elements. Membrane lipid analysis demonstrated age-dependent reductions and proximal to distal increases in total lipid (per milligram protein). Postnatal increases in membrane total cholesterol of jejunum (suckling vs. mature, 0.18 vs. 0.26 mumol/mg protein; P less than 0.01) and ileum (0.18 vs. 0.31 mumol/mg protein; P less than 0.01) resulted in markedly higher cholesterol-to-phospholipid molar ratios (jejunum, 0.43 vs. 0.73; ileum, 0.43 vs. 0.72 mumol/mg protein; P less than 0.01). Membranes from mature animals had higher relative sphingomeylin and phosphatidylcholine content and, in both age groups, fatty acyl saturation was increased in ileum compared with jejunum. By utilization of the fluorophores 1,6-diphenyl-1,3,5-hexatriene and DL-12-(9-anthroyl)stearic acid, the fluidity of basolateral membranes and liposomes prepared from extracted membrane lipid decreased markedly in mature rabbits. Arrhenius plots demonstrated higher apparent thermotropic transition temperatures of mature membrane lipid. These data therefore demonstrate significant changes in small intestinal basolateral membrane lipid composition and fluidity that occur during the weaning period. Possible relationships to ontogenesis of membrane protein function are discussed.