Adaptive regulation of brush-border amino acid transport in a chronic excluded jejunal limb

We examined the alterations in brush-border glutamine transport that occurred in a surgically defunctionalized jejunal limb excluded from mucosal food contact. Dogs were surgically prepared with Roux-en-Y gastrojejunostomies to permit same-intestine comparisons of glutamine transport and glutaminase activity in jejunal segments that were in incontinuity or excluded for a 6-mo period. Transport of glutamine, alanine, and glucose was measured in brush-border membrane vesicles prepared from each intestinal section; membrane marker enzymes were enriched to the same degree in incontinuity and excluded portions. The Na(+)-dependent glutamine cotransport apparent Km was the same in the excluded (779 +/- 63 microM) and incontinuity (873 +/- 105 microM) limbs. However, the Jmax for Na(+)-independent glutamine transport in the incontinuity jejunum (158.7 +/- 15.7 pmol.mg protein-1.s-1) was double that in the excluded limb (71.2 +/- 4.6 pmol.mg protein-1.s-1). Na(+)-dependent carrier-mediated glutamine transport rates were lower than the Na(+)-dependent system, but Na(+)-independent kinetic parameters were not significantly different in incontinuity vs. excluded limbs (Jmax 7.9 +/- 0.6 pmol.mg protein-1.s-1; Km 140 +/- 20 microM). Similarly, the passive diffusion permeability coefficient was the same for both excluded and incontinuity jejunal limbs (22.7 +/- 0.9 nl.mg protein-1.s-1). Mucosal glutaminase enzyme activity was increased by 28% in the incontinuity limb (4.32 +/- 0.21 vs. 3.36 +/- 0.35 mumol.mg protein-1.h-1; P less than 0.02). Transport rates of alanine and glucose were also diminished in the excluded limb (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)