Developmental changes in glucose transport, lipid composition, and fluidity of jejunal BBM.

Na(+)-dependent D-glucose uptake was studied in jejunal brush-border membrane (BBM) vesicles of chickens at 2 days and 1, 2, 5-6, and 12-14 wk of age. Both initial rates and accumulation ratios of the Na(+)-dependent D-glucose transport were significantly higher during the 1st wk than at other ages. To explain the age-related changes observed in the transport of D-glucose, the phlorizin-specific binding, Na+ permeability, lipid composition, and fluidity were studied. Transporter site density was quantified using 50 mumol/l phlorizin and found to be higher during the 1st wk. During the 2nd wk it decreased and then remained constant. Permeability of Na+, studied using 22Na+, showed that fluxes were similar during the first 6 wk, and a significant decrease was observed in the oldest group. Furthermore, membrane fluidity results showed a significant age-dependent decrease that correlated well with both the increased molar ratio of cholesterol to phospholipid and the decreased ratio of lipid to protein found during development. In conclusion, changes in the density of Na(+)-dependent D-glucose transporter as well as in lipid content and fluidity might be involved in the changes observed in D-glucose uptake during the posthatching development.