Transport of glutamine across blood-facing membranes of perfused rat jejunum.
Transport of glutamine and other neutral amino acids across the blood-facing membranes of isolated, dually perfused rat jejunum was measured using a paired-tracer isotope-dilution technique. Glutamine, asparagine, histidine, alanine, and leucine showed mutual inhibition of transport. The major component of physiological glutamine transport was saturable (Km = 0.88 +/- 0.15 mM, Vmax = 454 +/- 49 nmol.g-1.min-1; mean +/- SE), stereospecific and Na-independent and appeared to exhibit symmetry of glutamine transport; it most resembled system L. The minor Na-dependent component of glutamine transport resembled system A, i.e., it transported N-methylaminoisobutyric acid (Km approximately equal to 10 microM, Vmax approximately equal to 1.2 nmol.g-1.min-1). At 0.5 mM glutamine transport was insensitive to insulin and glucagon and was unaffected by perfusate pH (7.0-7.8). Glutamine extracted by the jejunum is rapidly utilized; at physiological blood glutamine concentrations the basolateral glutamine-transporter flux may thus not only restrict intestinal glutamine catabolism but also the consequent release of glutamine-derived ammonia (a substrate and stimulant of ureogenesis) into the portal circulation.
Taylor
P M
PM
Department of Anatomy and Physiology, University of Dundee, United Kingdom.
Egan
C J
CJ
Rennie
M J
MJ
D000596:Amino Acids / Q000378:metabolism; D000621:Aminoisobutyric Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001783:Blood Flow Velocity; D001808:Blood Vessels / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D005934:Glucagon / Q000494:pharmacology; D005973:Glutamine / Q000097:blood* / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000098:blood supply* / Q000378:metabolism; D007700:Kinetics; D008536:Meglumine / Q000494:pharmacology; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D000621:Aminoisobutyric Acids; D007328:Insulin; D005973:Glutamine; C017911:2-(methylamino)isobutyric acid; D008536:Meglumine; D005934:Glucagon; D012964:Sodium