Developmental Changes in Glutamine Transport by Rat Jejunal Basolateral Membrane Vesicles

The ontogeny of glutamine uptake by jejunal basolateral membrane vesicles (BLMV) was studied in suckling and weanling rats and the results were compared with adult rats. Glutamine uptake was found to represent a transport into an osmotically active space and not mere binding to the membrane surface. Temperature dependency indicated a carrier-mediated process with optimal pH of 7.0. Transport of glutamine was Na⁺ (out > in) gradient dependent with a distinct “overshoot” phenomenon. The magnitude of the overshoot was higher in suckling compared with weanling rats. The uptake kinetics and inhibition profile indicated the existence of two major transport pathways. A Na⁺-dependent system correlated with System A showed tolerance to System N and System ASC substrates, and a Na⁺-independent system similar to the classical L system that favors leucine and BCH. The V _max for the Na⁺-dependent system was higher in suckling compared with weanling and adult rats. The V _max for the Na⁺-dependent system was 0.86 ± 0.17, 0.64 ± 0.8, and 0.41 ± 0.9 nmol·mg protein^-1·10 sec^-1 for suckling, weanling, and adult rats, respectively. The V _max for the Na⁺-independent system was 0.68 ± 0.08, 0.50 ± 0.03, and 0.24 ± 0.03 nmol·mg protein^-1·10 sec^-1 for suckling, weanling, and adult rats, respectively. We conclude that glutamine uptake undergoes developmental changes consistent with more activity and/or number of glutamine transporters during periods of active cellular proliferation and differentiation.