Cotransport of organic solutes and sodium ions in the small intestine. General model. Amino acid transport (original) (raw)
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Biochimica et Biophysica Acta (BBA) - Biomembranes, 1982
L-Glutamate and L-aspartate transport into osmotically active intestinal brush border membrane vesicles is specifically increased by Na + gradient (extravesicular>intravesicular) which in addition energizes the transient accumulation (overshoot) of the two amino acids against their concentration gradients. The 'overshoot' is observed at minimal external Na + concentration of 100 mM for L-glutamate and 60 mM for L-aspartate; saturation with respect to [Na + ] was observed at a concentration near 100 mM for both amino acids. Increasing amino acid concentration, saturation of the uptake rate was observed for L-glutamate and L-aspartate in the concentration range between 1 and 2 mM. Experiments showing mutual inhibition and transtimulation of the two amino acids indicate that the same Na ÷ -dependent transport system is shared by the two acidic amino acids. The imposition of diffusion potentials across the membrane vesicles artificially induced by addition of valinomycin in the presence of a K ÷ gradient supports the conclusion that the cotransport Na+/dicarboxylic amino acid in rat brush border membrane vesicles is electroneutral.
The role of sodium ion in the transport of amino acids by the intestine
Biochimica et biophysica acta, 1965
I. Decreasing the incubation medium Na+ concentration below physiologic levels resulted in decreased transport of Na + and water in the isolated rabbit jejunum as well as diminution of amino acid transport. 2. Ouabain inhibited the transport of Na+ and amino acids in everted jejunal sacs. 3. Reduction of medium Na+ was associated with decreased tissue Na + and K+ content while ouabain produced elevated tissue Na+ and reduced tissue K+ concentrations. 4. Kinetic analysis of amino acid-uptake data showed that ouabain and reduction of medium Na + caused a slowing of both influx and, to a lesser degree, effiux coefficients. 5. The Na+ ion was shown to affect energy-independent (diffusion) as well as energy-dependent (active) transport of amino acids.
Alanine and Sodium Fluxes Across Mucosal Border of Rabbit Ileum
The Journal of General Physiology, 1967
The active transport of a variety of nonelectrolytes by animal cells appears to be dependent upon extracellular Na (1). For example, mucosal strips from rabbit ileum will accumulate L-alanine in an unbound, osmotically active form when incubated in a solution containing 140 m u Na. Removal of Na from the incubation medium has two effects on this process: (a) the rate of net alanine uptake is markedly reduced; and (b) the ability of the tissue to achieve an intracellular alanine concentration greater than that in the incubation medium is abolished (2). While these observations certainly implicate Na in the alanine transport process, they shed little light on the mechanism of the Na-amino acid interaction. Thus, inhibition of accumulation could result from a decreased influx into the tissue, an increased efflux out of the tissue, or a combination of both. Further, the preparations employed in studies of intestinal accumulation of nonelectrolytes do not distinguish between solute movements across the mucosal and across the serosal membranes of the cells.
Digestive diseases and sciences, 2000
Activation of intestinal Na+-glucose cotransport increases paracellular movement of inert tracers in cultured monolayers, isolated rodent intestinal mucosae, and in rodents in vivo. However, not all studies have demonstrated comparable effects on human intestinal paracellular absorption. We sought to assess the effects of Na+-glucose cotransport on paracellular absorption in human beings using a simple noninvasive assay. Study subjects drank six 200-ml doses of test solution, composed of 0.8% w/v creatinine (sufficient to overwhelm endogenous creatinine) in 277 mM glucose or mannitol and urine was collected. Intestinal creatinine absorption is paracellular. Once absorbed, creatinine is cleared into the urine. Therefore, urinary creatinine recovery reflects intestinal paracellular creatinine absorption. Total urinary creatinine recovery was 55% +/- 4% of creatinine ingested with glucose and 38% +/- 9% of creatinine ingested with mannitol (p < 0.001). Thus, intestinal paracellular ...
Amino acid transport by small intestinal, hepatic, and pancreatic epithelia
Gastroenterology, 1995
Abbreviations used in this paper: AIB, 2-aminoisobutyric acid; GGT, y-glutamyltranspeptidase; MeAIB, 2-(methylamino) isobutyric acid; NAA, neutral amino acid; NBAT, neutral and basic amino acid transporter; ORT, oral rehydration therapy; rBAT, related to b °'+ amino acid transporter; SGLT, sodium-dependent glucose transporter; Vm~x, maximum velocity.
The uptake of amino acids by the intestine
Biochimica et biophysica acta, 1954
It has been shown by WISEMAN 1 and AGAR, HIRD AND SIDHU 2 that isolated loops of rat's intestine transfer L-but not D-amino acids against a concentration gradient. These workers therefore suggested that the process of transfer was an active one. The discovery that cyanide and dinitrophenol interfered with this process (AGAR et al. ~)
Annals of Surgery, 1993
The effect of total parenteral nutrition (TPN) on small intestinal amino acid transport activity was studied in humans. Summary Background Data Studies in humans receiving TPN indicate that a decrease in the activities of the dissacharidase enzymes occurs, but morphologic changes are minimal with only a slight decrease in villous height. Methods Surgical patients were randomized to receive TPN (n = 6) or a regular oral diet (controls, n = 7) for 1 week before abdominal surgery. Ileum (5 controls, 5 TPN) or jejunum (2 controls, 1 TPN) were obtained intraoperatively and brush-border membrane vesicles (BBMV) were prepared by magnesium aggregation/differential centrifugation. Transport of L-MeAIB (a selective system A substrate), L-glutamine, L-alanine, L-arginine, L-leucine, and D-glucose was assayed by a rapid mixing/filtration technique in the presence and absence of sodium. Results Vesicles demonstrated approximately 18-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 1-hour equilibrium values. TPN resulted in a 26-44% decrease in the carrier-mediated transport velocity of all substrates except glutamine across ileal BBMVs. In the one patient receiving TPN from whom jejunum was obtained, there was also a generalized decrease in nutrient transport, although glutamine was least affected. Kinetic studies of the system A transporter demonstrated that the decrease in uptake was secondary to a reduction in carrier Vm., consistent with a decrease in the number of functional carriers in the brush-border membrane. Conclusions TPN results in a decrease in brush-border amino acid and glucose transport activity. The observation that glutamine transport is not downregulated by 1 week of bowel rest may further emphasize the important metabolic role that glutamine plays as a gut fuel and in the body's response to catabolic stresses.