Development of brush-border membrane hexose transport system in chick jejunum.

Hexose transport was characterized in jejunal slices and brush-border membrane (BBM) vesicles from chicks of several ages (range: 2 days before hatch to 21 days after hatch). With slices, initial rates of 0.1 mM 3-O-methyl-D-glucose transport were low in --2-, and 0-day chicks, increasing to maximal levels 2-7 days after hatching; rates declined to adult levels over the next 2 wk. Phlorizin did not inhibit uptakes in --2- or 0-day slices. In contrast, about 80% of the uptakes in tissue from 2-day or older chicks was phlorizin inhibitable. The apparent Kt for phlorizin-sensitive transport was the same in slices from 2- (maximal transport rates) and 21-day (minimal posthatch rates) chicks; the apparent Vmax was 2.5 times greater in 2-day slices. With BBM vesicles, initial rates of Na-dependent D-glucose transport and maximal overshoot levels were greater in 2-day vesicles than in 21-day vesicles. As in slice experiments, Kt values were the same in the two preparations, but Vmax values were 1.4 times higher in the 2-day preparation.