THE DEVELOPMENT OF THE GLUCOSE, MYO-INOSITOL, GLUTAMIC ACID, CHOLINE AND BETA-ALANINE TRANSPORT SYSTEMS IN THE CHICK SMALL INTESTINE

Hexose (D-glucose and 3-O-methyl-D-glucose), myo-inositol, glutamic acid, choline, and (beta)-alanine transports were characterized in jejunal slices and brush-border membrane (BBM) vesicles from chicks of varying ages (range: 3 days before hatch to 21 days after hatch). With slices, mediated transport activities of 3-O-methyl-D-glucose, myo-inositol and (beta)-alanine were low before hatch. These activities were found to increase at the time of hatch, reaching maximal levels 2-7 days after hatch for 3-O-methyl-D-glucose, and 3-5 days after hatch for (beta)-alanine; activities declined to adult levels over the next 2 wk. Transport activity of myo-inositol increased during the same time period. For the glutamic acid transport system, mediated transport was higher in 2 d slices than in 21 d slices, whereas mediated transport of choline remained the same during this developmental period. For the hexose transport system, the apparent Kt for phloridzin-sensitive transport (mediated route) was the same in slices from 2-day (peak transport rates) and 21-day (minimal posthatch rates) chicks; the apparent Vmax was 2.5 times greater in 2-day slices.; The apparent diffusion coefficients (Kd) for (alpha)-methylglucoside-, aspartic acid-, hemicholinium- and proline-insensitive transport of myo-inositol, glutamic acid, choline and (beta)-alanine, respectively, were the same in slices from 2- and 21-day chicks. In contrast, the Kd for phloridzin-insensitive transport of 3-O-methyl-D-glucose was 70% greater in 2-day slices than in 21-day slices.; With BBM vesicles, Na-dependent transport rates of D-glucose, glutamic acid and (beta)-alanine were greater in 2-day vesicles than in 21-day vesicles, whereas Na-dependent transport rates of myo-inositol were greater in 21-day vesicles than in 2-day vesicles. Transport rates of choline were the same in 2-day and 21-day vesicles. As in slice experiments, Kt values for phloridzin-sensitive transport of D-glucose were the same in the two preparations, but Vmax values were 1.4 times higher in the 2-day preparation.; Chick jejunal slices that were exposed to HgCl(,2) exhibited markedly reduced uptakes of D-glucose. The carrier-mediated, but not diffusive, component of uptake was affected by Hg. Within each age group, I(,50) values (concentration of HgCl(,2) causing 50% inhibition of mediated transport) for slices (mucosal plus serosal exposure) and sacs (mucosal exposure only) were nearly identical: values for BBM vesicles were slightly lower (increased sensitivity). For each preparation, I(,50) values for 2-day chicks were consistently lower than corresponding values for 21-day chicks.; Data from biochemical experiments with 2-day and 21-day BBM preparations indicate the following: (a) the total lipid, lipid phosphorus and cholesterol contents per mg membrane protein were higher in the 2-day preparation, (b) the cholesterol-to-phospholipid mole ratio was higher in the 21-day preparation, and (c) the total fatty acid content per mg membrane protein was higher in the 2-day preparation.; Taken together, these data indicate the following: (a) changes in the chick intestinal BBM are responsible for the observed changes in substrate transport by jejunal slices during development, (b) that the transport systems have different developmental timetables, (c) that changes in transport activity during development may be partly due to changes in the membrane fluidity of the BBM, and (d) that the jejunal BBM is a site of HgCl action and that membrane sites in tissue from 2-day chicks are more sensitive to Hg than similar sites in tissue from 21-day chicks.