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)
Salloum
R M
RM
Department of Surgery, University of Florida College of Medicine, Gainesville.
Stevens
B R
BR
Souba
W W
WW
D000409:Alanine / Q000378:metabolism; D000713:Anastomosis, Roux-en-Y; D001216:Asparagine / Q000378:metabolism; D001693:Biological Transport, Active; D005947:Glucose / Q000378:metabolism; D005972:Glutaminase / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D006639:Histidine / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism* / Q000601:surgery / Q000648:ultrastructure; D007700:Kinetics; D008871:Microvilli / Q000201:enzymology / Q000378:metabolism; D012964:Sodium / Q000502:physiology
D005973:Glutamine; D006639:Histidine; D001216:Asparagine; D012964:Sodium; D005972:Glutaminase; D005947:Glucose; D000409:Alanine