Kidney Brush-border Membrane Vesicles Research Articles

The mechanism of Na+-L-lactate cotransport by brush-border membrane vesicles from horse kidney. Analysis by isotopic exchange kinetics of a sequential model and stoichiometry.

The present study determines the characteristics of isotopic Na and lactate exchange under equilibrium conditions in horse kidney brush-border membrane vesicles. The influence of one solute (Na+ or lactate) on the isotopic exchange of the co-transported species (lactate or Na) was analyzed in detail. Analysis of the data suggests that Na and lactate interact sequentially with the carrier. The observed apparent symmetry between the activating effect of low Na concentrations and the inhibiting effect of high Na concentrations on the lactate exchange process suggests that the carrier functions according to a glide symmetry model where the two solutes bind to the carrier according to an iso-ordered Bi Bi process. This conclusion is strengthened by the properties of the 22Na exchange process catalyzed by the lactate carrier. Direct measurement under equilibrium conditions of the coupled Na+/lactate transport indicated a stoichiometry of 2:1. These data, along with those obtained in a previous study (Mengual R., and Sudaka P. (1983) J. Membr. Biol. 71, 163-171) allow us to propose a mechanism for the Na+-lactate cotransport, involving a transport system that functions according to an iso-ordered Bi Bi process where binding and debinding of Na+ occur first, followed by the lactate molecule.

Isolation of the sodium-dependent d-glucose transport protein from brush-border membranes

Rabbit kidney brush-border membrane vesicles were exposed to bacterial protease which cleaves off a large number of externally oriented proteins. Na +-dependent d-glucose transport is left intact in the protease-treated vesicles. The protease-treated membrane was solubilized with deoxycholate and the deoxycholate-extracted proteins were further resolved by passage through Con A-Sepharose columns. Sodium-dependent d-glucose activity was found to reside in a fraction containing a single protein band of M r ≅ 165000 which is apparently a dimer of M r ≅ 85 000. When reconstituted and tested for transport, this protein showed Na +-dependent, stereo-specific and phlorizin-inhibitable glucose transport. Transport activity is completely recovered and is 20-fold increased in specific activity. A similar isolate was obtained from rabbit small intestinal brush-border membranes and kidneys from several other species of animals.

Influence of sodium ions on detergent solubilization of pig brush border D-glucose transport system for reconstitution experiments

The D-glucose uptake by liposomes resulting from the association of egg lecithins with solubilized membrane proteins was measured in order to assess their sodium dependent D-glucose transport activity. Membrane proteins were extracted by Triton X-100 solubilization of pig kidney brush border membrane vesicles, which were suspended either in KCl medium or in NaCl medium. When measured by equilibrium isotope exchange procedure in sodium conditions, the D-glucose uptake by sodium detergent extract associated to liposomes occurred with a higher velocity than that obtained with liposomes reconstituted from potassium detergent extract. No differences were observed in the permeability or in the protein content of two types of liposomes. These results are discussed in terms of activation of D-glucose transport system induced by sodium ions before membrane protein solubilization.

Participation of alkaline phosphatase in the active transport of phosphates in brush border membrane vesicles

Hamster and rat kidney brush border membrane vesicles were compared for their ability to transport phosphate in vitro . In presence of 0.1 mM inorganic phosphate, the Na + dependent uptake was greater in rat than in hamster but the Km values for uptake were respectively 0.32 mM and 0.12 mM for hamster and rat. In presence of glycerophosphate, as sole source of phosphate, only hydrolysed phosphate was transported but in a much greater amount (× 10) than the one expected from the actual concentration of inorganic phosphate released by the action of alkaline phosphatase during the course of the experiments. Although the Na + dependent uptake of phosphate from glycerophosphate relied on alkaline phosphatase action, the extent of transport did not seem to be correlated to the amount of catalytic activity present, pointing to a concerted action between alkaline phosphatase and the phosphate carrier.

Transport of glutamine by rat kidney brush-border membrane vesicles.

Transport of glutamine by brush-border vesicles prepared from the renal cortex was studied. The transport system had both Na+-dependent and Na+-independent components. The presence of Na+ in the incubation resulted in an 'overshoot' at 30s at which time the rates of transport were approx. 8 times the values obtained in the absence of Na+. Variation of the glutamine concentration showed that the system obeyed Michaelis-Menten kinetics with Km and Vmax. values for the Na+-dependent system of 0.86 mM and 9.6 nmol/min per mg of protein respectively. Vesicles obtained from chronically acidotic rats showed similar kinetic characteristics. The Km and Vmax. values for the Na+-dependent system were 0.76 mM and 9.6 nmol/min per mg of protein respectively. There was increased uptake of glutamine by vesicles from acidotic rats and this increase was associated with increased activity of gamma-glutamyltransferase in these preparations. Vesicles from acidotic rats, however, showed no increase in glucose transport and no increase in the activity of maltase, another brush-border enzyme.

L-proline transport by newborn rat kidney brush-border membrane vesicles

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.

On the maleic acid induced Fanconi syndrome: Effects on transport by isolated rat kidney brushborder membrane vesicles

The association of maleic acid with isolated rat kidney brushborder membranes and the effect of maleic acid on uptake of amino acids and α-methyl-D-glucoside by brushborder membrane vesicles has been studied. Although maleic acid associates with the membrane, no alteration of sodium dependent transport of these substrates into the vesicles was observed. These findings indicate that the maleic acid induced Fanconi syndrome in the rat with aminoaciduria and glycosuria is not due to a direct, adverse effect on the renal tubule brushborder membrane per se .

Gills and kidneys in ureosmotic regulation in euryhaline skates.

Gills and kidneys in ureosmotic regulation in euryhaline skates.

Osmoregulation and urea metabolism in the little skate Raja erinacea.

Osmoregulation and urea metabolism in the little skate Raja erinacea.