Kinetic analysis of L-glutamine transport into porcine jejunal enterocyte brush-border membrane vesicles

L-Glutamine transport into porcine jejunal enterocyte brush border membrane vesicles was studied. Uptake was mediated by a Na+-dependent and a Na+-ind ependent pathway as well as by diffusion. The initial rates of glutamine up take over a range of concentrations in both Na+-independent and Na+-free co nditions were analyzed and kinetic parameters were obtained. Na+-dependent glutamine transport had a K-m of 0.77 +/- 0.16 mM and a J(max) of 70.7 +/- 5.8 pmol mg protein(-1) s(-1); Na+-independent glutamine transport had a K- m of 3.55 +/- 0.78 mM and a J(max) of 55.1 +/- 6.6 pmol mg protein(-1) s(-1 ). The non-saturable component measured with HgCl2-poisoned brush border me mbrane vesicles in the Na+-free condition contained passive diffusion and n on-specific membrane binding and was defined to be apparent glutamine diffu sion and the glutamine permeability coefficient (K-diff) was estimated to b e K-diff = 3.78 +/- 0.06 pmol 1 mg protein(-1) mmol(-1) s(-1). Results of i nhibition experiments showed that Na+-dependent glutamine uptake occurred p rimarily through the brush border system-B-o transporters, whereas Na+-inde pendent glutamine uptake occurred via the system-L transporters. Furthermor e, the kinetics of L-leucine and L-cysteine inhibition of L-glutamine uptak e demonstrated that neutral amino acids sharing the same brush border trans porters can effectively inhibit each other in their transport. (C) 1998 Els evier Science Inc. All rights reserved.