Intestinal membrane lipid composition and fluidity during development in the rat.

We have characterized microvillus membrane (MVM) lipid composition and derived estimates of membrane fluidity using fluorescence polarization [with 1,6-diphenyl-1,3,5-hexatriene (DPH) as the probe] in MVM from the jejunum and ileum of suckling (day 14-20) and mature postweaning (day 28-49) rats. The anisotropic values are lower (i.e., increased fluidity) in MVM from jejunum and ileum of suckling rats compared with values from MVM of mature rats, suggesting a more disordered molecular environment in MVMs of suckling animals, although the ileal MVM was relatively less fluid than jejunal membranes in both groups. Anisotropic determinations in protein-free MVM liposomes demonstrate that protein-lipid interactions are major determinants of fluidity estimates. Arrhenius plots of DPH anisotropies in MVM and MVM liposomes indicate a thermotropic lipid-phase transition at 23 degrees C in mature rat jejunum and ileum; however, no clear transition point was observed in 14- to 20-day animals. In addition, both the jejunal and ileal MVM in suckling animals contained greater amounts of total lipid, cholesterol, and phospholipid per milligram protein than did mature MVM preparations. Membrane phospholipid composition changed with age, with a decrease in sphingomyelin and an increase in phosphatidylcholine in the jejunum of the postweaning animal and with similar weight ratios of saturated to unsaturated fatty acids in both age groups. The data demonstrate that the small intestinal MVM manifests both age-dependent and regional proximal-distal differences in lipid composition and biophysical properties.(ABSTRACT TRUNCATED AT 250 WORDS)