Transport of glutamine by rat kidney brush-border membrane vesicles.
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ABSTRACT:
SUBMITTER: McFarlane-Anderson N
PROVIDER: S-EPMC1161307 | biostudies-other | 1979 Aug
REPOSITORIES: biostudies-other
Similar Datasets
Project description:The transport of L-proline was studied in brush-border membrane vesicles isolated from the kidneys of newborn rats. In contrast with the rapid initial uptake with an 'overshoot' observed in adult vesicles, uptake by the newborn vesicle was slow, showed no 'overshoot', and proline continued to accumulate at a time when the adult vesicle had already equilibrated. L-Proline transport in the newborn rat occurs by Na+-dependent and independent mechanisms. There appeared to be essentially no uptake by anti-luminal vesicles isolated from newborn rat kidney. These observations may help to explain the prolinuria that occurs in the newborn animal.
| S-EPMC1186506 | biostudies-other
Project description:In the presence of a 100 mM Na+ gradient, transport of L-carnitine into rat renal brush-border-membrane vesicles was linear over 30 s and showed an overshoot at 5 min. The uptake of L-carnitine was clearly less active in the presence of other cations such as Li+, K+, Cs+ or choline. In the presence of a Na+ gradient, L-carnitine uptake after 20 s was much higher for chloride as an anion than for SCN-, NO3-, gluconate or SO4(2-). In comparison with conditions with inside positive or no membrane potential, transport was higher in vesicles with an inside negative membrane potential, suggesting an electrogenic mechanism. The kinetic characterization of the Na(+)-dependent portion of L-carnitine transport revealed two transport systems with Km values of 17.4 +/- 3.9 microM and 15.0 +/- 6.0 mM, respectively. The transport could be inhibited in a concentration-dependent fashion by structural analogues such as butyrobetaine, L-acetylcarnitine, trimethyl-lysine and D-carnitine, but not by L-arginine or glycinebetaine.
| S-EPMC1135779 | biostudies-other
Project description:Glutamine uptake was examined in isolated renal brush-border and basolateral-membrane vesicles from control and acidotic rats. In brush-border vesicles from acidotic animals, there was a significant increase in the initial rate of glutamine uptake compared with that in controls. Lowering the pH of the medium increased the initial rate of glutamine uptake in brush-border vesicles from acidotic, but not from control, rats. In brush-border vesicles from both groups of animals, two saturable transport systems mediated glutamine uptake. There was a 2-fold increase in the Vmax. of the low-affinity high-capacity system in the brush-border vesicles from the acidotic animals compared with that from control animals, with no alteration in the other kinetic parameters. There was no difference in glutamine uptake by the two saturable transport systems in basolateral vesicles from control and acidotic animals. Lowering the incubation-medium pH increased the uptake of glutamine by basolateral vesicles from both control and acidotic rats to a similar extent. The data indicate that during acidosis there are alterations in glutamine transport by both the basolateral and brush-border membrane which could enhance its uptake by the renal-tubule cell for use in ammoniagenesis.
| S-EPMC1153148 | biostudies-other
Project description:Uptake of SO(4) (2-) into brush-border membrane vesicles isolated from rat kindey cortex by a Ca(2+)-precipitation method was investigated by using a rapid-filtration technique. Uptake of SO(4) (2-) by the vesicles was osmotically sensitive and represented transport into an intra-vesicular space. Transport of SO(4) (2-) by brush-border membranes was stimulated in the presence of Na(+), compared with the presence of K(+) or other univalent cations. A typical ;overshoot' phenomenon was observed in the presence of an NaCl gradient (100mm-Na(+) outside/zero mm-Na(+) inside). Radioactive-SO(4) (2-) exchange was faster in the presence of Na(+) than in the presence of K(+). Addition of gramicidin-D, an ionophore for univalent cations, decreased the Na(+)-gradient-driven SO(4) (2-) uptake. SO(4) (2-) uptake was only saturable in the presence of Na(+). Counter-transport of Na(+)-dependent SO(4) (2-) transport was shown with MoO(4) (2-) and S(2)O(3) (2-), but not with PO(4) (2-). Changing the electrical potential difference across the vesicle membrane by establishing different diffusion potentials (anion replacement; K(+) gradient+/-valinomycin) was not able to alter Na(+)-dependent SO(4) (2-) uptake. The experiments indicate the presence of an electroneutral Na(+)/SO(4) (2-)-co-transport system in brush-border membrane vesicles isolated from rat kidney cortex.
| S-EPMC1161252 | biostudies-other
Project description:Taurine transport in isolated brush-border-membrane vesicles from rat kidney is concentrative and it is driven by the Na+ gradient and transmembrane potential difference; binding is not a significant component of net uptake. The Na+-dependent component of net uptake is saturable with an apparent Km of 17 microM. The taurine-transport mechanism is selective for beta-amino compounds.
| S-EPMC1161041 | biostudies-other
Project description:Uptake of Pi into brush-border membrane vesicles isolated from rat small intestine was investigated by a rapid filtration technique. The following results were obtained. 1. At pH 7.4 in the presence of a NaCl gradient across the membrane (sodium concentration in the medium higher than sodium concentration in the vesicles), phosphate was taken up by a saturable transport system, which was competitively inhibited by arsenate. Phosphate entered the same osmotically reactive space as D-glucose, which indicates that transport into the vesicles rather than binding to the membranes was determined. 2. The amount of phosphate taken up initially was increased about fourfold by lowering the pH from 7.4 to 6.0.3. When Na+ was replaced by K+, Rb+ or Cs+, the initial rate of uptake decreased at pH 7.4 but was not altered at pH 6.0.4. Experiments with different anions (SCN-,Cl-, SO42-) and with ionophores (valinomycin, monactin) showed that at pH 7.4 phosphate transport in the presence of a Na+ gradient is almost independent of the electrical potential across the vesicle membrane, whereas at pH 6.0 phosphate transport involves the transfer of negative charge. It is concluded that intestinal brush-border membranes contain a Na+/phosphate co-transport system, which catalyses under physiological conditions an electroneutral entry of Pi and Na+ into the intestinal epithelial cell. In contrast with the kidney, probably univalent phosphate and one Na+ ion instead of bivalent phosphate and two Na+ ions are transported together.
| S-EPMC1164262 | biostudies-other
Project description:Uptake of taurocholate into brush-border membrane vesicles isolated from rat small intestine by a Ca(2+) -precipitation method was investigated by using a rapid-filtration technique. Uptake of taurocholate by ileal brush-border membranes consisted of three phenomena: binding to the outside of the vesicles, transfer across the vesicle membrane and binding to the intravesicular compartment. The transport of taurocholate across the brush-border membranes was stimulated in the presence of Na(+) compared with the presence of K(+); stimulation was about 11-fold in the presence of a NaCl gradient (Na(o)>Na(i)), where the subscripts refer to ;outside' and ;inside' respectively, and 4-fold under equilibrium conditions for Na(+) (Na(o)=Na(i)). In the presence of a Na(+) gradient a typical ;overshoot' phenomenon was observed. Membranes preloaded with unlabelled taurocholate showed an accelerated entry of labelled taurocholate (tracer exchange) in the presence of Na(+) compared with the presence of K(+). The stimulation by Na(+) was observed only in membrane preparations from the ileum. Addition of monactin, an ionophore for univalent cations, decreased the Na(+)-gradient-driven taurocholate uptake. The Na(+)-dependent taurocholate transport showed saturation kinetics and the phenomenon of counterflow and was inhibited by glycocholate. Other cations such as Li(+), Rb(+) and Cs(+) could not replace Na(+) in its stimulatory action. When the electrical potential difference across the vesicle membrane was altered by establishing different diffusion potentials (anion replacement; K(+) gradient+/-valinomycin) a more-negative potential inside stimulated Na(+)-dependent taurocholate transport. These data demonstrate the presence of a rheogenic (potential sensitive) Na(+)-taurocholate co-transport system in ileal brush-border membranes and support the hypothesis that the reabsorption of bile acids in the ileum is a secondary active uptake.
| S-EPMC1186000 | biostudies-other
Project description:The characteristics of tryptophan uptake in isolated human placental brush-border membrane vesicles were investigated. Tryptophan uptake in these vesicles was predominantly Na+-independent. Uptake of tryptophan as measured with short incubations occurred exclusively by a carrier-mediated process, but significant binding of this amino acid to the membrane vesicles was observed with longer incubations. The carrier-mediated system obeyed Michaelis-Menten kinetics, with an apparent affinity constant of 12.7 +/- 1.0 microM and a maximal velocity of 91 +/- 5 pmol/15 s per mg of protein. The kinetic constants were similar in the presence and absence of a Na+ gradient. Competition experiments showed that tryptophan uptake was effectively inhibited by many neutral amino acids except proline, hydroxyproline and 2-(methylamino)isobutyric acid. The inhibitory amino acids included aromatic amino acids as well as other system-1-specific amino acids (system 1 refers to the classical L system, according to the most recent nomenclature of amino acid transport systems). The transport system showed very low affinity for D-isomers, was not affected by phloretin or glucose but was inhibited by p-azidophenylalanine and N-ethylmaleimide. The uptake rates were only minimally affected by change in pH over the range 4.5-8.0. Tryptophan uptake markedly responded to trans-stimulation, and the amino acids capable of causing trans-stimulation included all amino acids with system-1-specificity. The patterns of inhibition of uptake of tryptophan and leucine by various amino acids were very similar. We conclude that system t, which is specific for aromatic amino acids, is absent from human placenta and that tryptophan transport in this tissue occurs via system 1, which has very broad specificity.
| S-EPMC1147116 | biostudies-other
Project description:Studies on proton and Na+ transport by isolated intestinal and renal brush-border-membrane vesicles were carried out to test for the presence of an Na+/H+-exchange system. Proton transport was evaluated as proton transfer from the intravesicular space to the incubation medium by monitoring pH changes in the membrane suspension induced by sudden addition of cations. Na+ transport was determined as Na+ uptake into the vesicles by filtration technique. A sudden addition of sodium salts (but not choline) to the membrane suspension provokes an acidification of the incubation medium which is abolished by the addition of 0.5% Triton X-100. Pretreatment of the membranes with Triton X-100 prevents the acidification. The acidification is also not observed if the [K+] and proton conductance of the membranes have been increased by the simultaneous addition of valinomycin and carbonyl cyanide p-trifluoromethoxyphenylhydrazone to the K+-rich incubation medium. Either valinomycin or carbonyl cyanide p-trifluoromethoxyphenylhydrazone when added alone do not alter the response of the membranes to the addition of Na+. Na+ uptake by brush-border microvilli is enhanced in the presence of a proton gradient directed from the intravesicular space to the incubation medium. Under these conditions a transient accumulation of Na+ inside the vesicles is observed. It is concluded that intestinal and renal brush-border membranes contain a NA+/H+ antiport system which catalyses an electroneutral exchange of Na+ against protons and consequently can produce a proton gradient in the presence of a concentration difference for Na+. This system might be involved in the active proton secretion of the small intestine and the proximal tubule of the kidney.
| S-EPMC1172760 | biostudies-other
Project description:The effect of phenylglyoxylation on brush-border-membrane functions was studied with membrane vesicles from rat kidney cortex. Na+-gradient-dependent uptake of phosphate, glucose and alanine was inhibited by 65, 88 and 70% by pre-incubation of vesicles with 50 mM-phenylglyoxal for 2 min. The inhibition showed a dependency for alkaline pH. Borate co-operativity in butanedione inactivation was used to prove that inhibition was caused by arginine modification. Intravesicular volumes, alkaline phosphatase, aminopeptidase M and Na+-H+ exchange were not affected by phenylglyoxal treatment. Inhibition of phosphate uptake was studied in more detail and showed that the chemical modification introduced by phenylglyoxal inhibited the overshoot of phosphate uptake caused by the Na+ gradient, and decreased the apparent maximal velocity of the phosphate-transport system in its interaction with Na+. Phosphate uptake measured in the absence of Na+ was not affected by phenylglyoxal. Shunting of the transmembrane electrical potential with K+ and valinomycin had no effect on phenylglyoxal inhibition, proving that the alteration of transmembrane electrical potential could not be responsible for this effect. Phenylglyoxal had no ionophoric effect on the Na+ gradients studied (1-100 mM). Na+ efflux was also unaffected by phenylglyoxal treatment. Na+, harmaline and amiloride were ineffective in protecting against phenylglyoxal inhibition, suggesting that the site modified was not an Na+-binding site. These results indicate the involvement of highly reactive arginine residues in phosphate, glucose and alanine uptake.
| S-EPMC1144364 | biostudies-other