AJP - Gastrointestinal and Liver Physiology, Vol 261, Issue 1 22-G27, Copyright © 1991 by American Physiological Society
Adaptive regulation of brush-border amino acid transport in a chronic excluded jejunal limb
R. M. Salloum, B. R. Stevens and W. W. Souba
Department of Surgery, University of Florida College of Medicine, Gainesville.
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)
