Na+-gradient-dependent stimulation of renal transport of rho-aminohippurate.
Ontology highlight
ABSTRACT:
SUBMITTER: Sheikh MI
PROVIDER: S-EPMC1153953 | biostudies-other | 1982 Oct
REPOSITORIES: biostudies-other
Similar Datasets
Project description:The transport properties for phenylalanine and glucose in luminal-membrane vesicles from outer cortex (pars convoluta) and outer medulla (pars recta) of rabbit kidney were studied by a spectrophotometric method. Uptake of phenylalanine as well as of glucose by the two types of membrane vesicles was found to be Na+-dependent, electrogenic and stereospecific. Na+-dependent transport of L-phenylalanine by outer-cortical membrane vesicles could be accounted for by one transport system (KA congruent to 1.5 mM). By contrast, in the outer-medullary preparation, L-phenylalanine transport occurred via two transport systems, namely a high-affinity system with K1A congruent to 0.33 mM and a low-affinity system with K2A congruent to 7 mM respectively. Na+-dependent uptake of D-glucose by pars convoluta and pars recta membrane vesicles could be described by single, but different, transport systems, namely a low-affinity system with KA congruent to 3.5 mM and a high-affinity system with KA congruent to 0.30 mM respectively. Attempts to calculate the stoichiometry of the different Na+/D-glucose transport systems by using Hill-type plots revealed that the ratio of the Na+/hexose co-transport probably is 1:1 in the case of pars convoluta and 2:1 in membrane vesicles from pars recta. The Na+/L-phenylalanine stoichiometry of the pars convoluta transporter probably is 1:1. Both the high-affinity and the low-affinity Na+-dependent L-phenylalanine transport system of pars recta membrane vesicles seem to operate with a 1:1 stoichiometry. The physiological importance of the arrangement of low-affinity and high-affinity transport systems along the kidney proximal tubule is discussed.
| S-EPMC1153589 | biostudies-other
Project description:L-Carnitine transport was characterized in Xenopus laevis oocytes before and after injection of mRNA isolated from rat renal cortex. Non-injected oocytes revealed endogenous Na(+)-dependent transport of L-carnitine. After injection of 15 ng of rat kidney mRNA, the Na(+)-dependent L-carnitine transport increased 2-3-fold, reaching maximal activity after 5-6 days. The expressed carnitine transport was maximal at pH 7.5, whereas the endogenous transport showed no clear maximum between pH 6.0 and 8.5. Kinetic analysis revealed apparent Km values for L-carnitine of 66 microM for the endogenous and 149 microM for the expressed transport. Trimethyl-lysine and D-carnitine inhibited both the endogenous and the expressed transport. In contrast, L-acetylcarnitine, L-isovalerylcarnitine, L-palmitoylcarnitine and butyrobetaine inhibited predominantly the expressed transport, whereas glycinebetaine had no inhibitory effect on either transport system. Size-fractionated rat renal-cortex mRNA (median size 2 kb) induced a 3-fold higher L-carnitine transport than did unfractionated mRNA. These studies demonstrate that Xenopus laevis oocytes exhibit Na(+)-dependent L-carnitine transport and provide the basis for expression-cloning of a rat renal Na(+)-dependent L-carnitine transport system.
| S-EPMC1135744 | biostudies-other
Project description:A monoclonal antibody FD19 which removes reconstitutable Na(+)-dependent amino acid transport activity from solubilized bovine renal brush-border membrane vesicles was found to react specifically with the enzyme aminopeptidase N. Cleavage of aminopeptidase N from the membranes with papain inhibited Na(+)-dependent amino acid transport activity without affecting that of alpha-methyl D-glucoside. Removal of aminopeptidase substantially increased the Km values for the Na(+)-dependent transport of alanine, glutamine, leucine and phenylalanine without affecting the Vmax. Both Na(+)-dependent amino acid transport and aminopeptidase activity in intact vesicles were competitively inhibited by amino acids with very similar specificity. These results suggest that the amino acid-binding sites of aminopeptidase N and the transporter interact in some way to increase the Km of the transport process for its substrates. However, independent direct inactivation of the transport system by papain cannot be ruled out.
| S-EPMC1132382 | biostudies-other
Project description:Tolerance to high soil [Na(+)] involves processes in many different parts of the plant, and is manifested in a wide range of specializations at disparate levels of organization, such as gross morphology, membrane transport, biochemistry and gene transcription. Multiple adaptations to high [Na(+)] operate concurrently within a particular plant, and mechanisms of tolerance show large taxonomic variation. These mechanisms can occur in all cells within the plant, or can occur in specific cell types, reflecting adaptations at two major levels of organization: those that confer tolerance to individual cells, and those that contribute to tolerance not of cells per se, but of the whole plant. Salt-tolerant cells can contribute to salt tolerance of plants; but we suggest that equally important in a wide range of conditions are processes involving the management of Na(+) movements within the plant. These require specific cell types in specific locations within the plant catalysing transport in a coordinated manner. For further understanding of whole plant tolerance, we require more knowledge of cell-specific transport processes and the consequences of manipulation of transporters and signalling elements in specific cell types.
| S-EPMC4242248 | biostudies-literature
Project description:The stoichiometric properties of Na+- and H+-dependent L-alanine transporters recently identified in luminal-membrane vesicles prepared from proximal convoluted tubules (pars convoluta) and proximal straight tubules (pars recta) of rabbit kidney were studied. We provide indirect evidence suggesting that one Na+ and one H+ ion are co-transported with the L-alanine molecule via Na+-dependent and H+-dependent transport systems located in vesicles from pars convoluta. Furthermore, our experimental data suggest that both the high-affinity and the low-affinity Na+-dependent L-alanine transport systems of pars recta vesicles operate with a 1:1 stoichiometry.
| S-EPMC1135403 | biostudies-other
Project description:The short-term protein-synthesis-independent stimulation of alanine transport in hepatocytes was further investigated. Cyclic AMP increased the Vmax. of alanine transport. Amino acid transport via systems A, ASC and N was stimulated. A good correlation was found between the initial rate of transport and the cell membrane potential as calculated from the distribution of Cl-. Cyclic AMP increased the rate of alanine transport, stimulated Na+/K+ ATPase (Na+/K+-transporting ATPase) activity and caused membrane hyperpolarization. The time courses and cyclic AMP dose-dependencies of all three effects were similar. Ouabain abolished the effect of cyclic AMP on Cl- distribution and on transport of alanine. The effect of cyclic AMP on alanine transport and Cl- distribution was mimicked by the antibiotic nigericin; the effect of nigericin was also abolished by ouabain. It is concluded that the effect of cyclic AMP on transport is mediated via membrane hyperpolarization. It is suggested that the primary action of cyclic AMP is to increase the activity of an electroneutral Na+/K+-exchange system in the liver cell plasma membrane, thus hyperpolarizing the membrane by stimulating the electrogenic Na+/K+ ATPase.
| S-EPMC1147625 | biostudies-other
Project description:1. A simple and rapid method for the reconstitution of Na+-dependent neutral amino acid transport activity from bovine renal brush border membranes is described. 2. The neutral detergent decanoyl-N-methylglucamide ('MEGA-10') was employed to solubilize the membrane protein. This obviated the necessity for a prolonged dialysis step. 3. The properties of amino acid transport in these vesicles were similar to those observed in native membranes. 4. This should be a useful procedure in the eventual identification and isolation of amino acid transport proteins.
| S-EPMC1148024 | biostudies-other
Project description:Extracellular ?-synuclein (?-syn) assemblies can be up-taken by neurons; however, their interaction with the plasma membrane and proteins has not been studied specifically. Here we demonstrate that ?-syn assemblies form clusters within the plasma membrane of neurons. Using a proteomic-based approach, we identify the ?3-subunit of Na+/K+-ATPase (NKA) as a cell surface partner of ?-syn assemblies. The interaction strength depended on the state of ?-syn, fibrils being the strongest, oligomers weak, and monomers none. Mutations within the neuron-specific ?3-subunit are linked to rapid-onset dystonia Parkinsonism (RDP) and alternating hemiplegia of childhood (AHC). We show that freely diffusing ?3-NKA are trapped within ?-syn clusters resulting in ?3-NKA redistribution and formation of larger nanoclusters. This creates regions within the plasma membrane with reduced local densities of ?3-NKA, thereby decreasing the efficiency of Na+ extrusion following stimulus. Thus, interactions of ?3-NKA with extracellular ?-syn assemblies reduce its pumping activity as its mutations in RDP/AHC.
| S-EPMC4601662 | biostudies-literature
Project description:Our previous work in 293T cells and AF17(-/-) mice suggests that AF17 upregulates expression and activity of the epithelial Na(+) channel (ENaC), possibly by relieving Dot1a-AF9-mediated repression. However, whether and how AF17 directly regulates Dot1a cellular distribution and ENaC function in renal collecting duct cells remain unaddressed. Here, we report our findings in mouse cortical collecting duct M-1 cells that overexpression of AF17 led to preferential distribution of Dot1a in the cytoplasm. This effect could be blocked by nuclear export inhibitor leptomycin B. siRNA-mediated depletion of AF17 caused nuclear accumulation of Dot1a. AF17 overexpression elicited multiple effects that are reminiscent of aldosterone action. These effects include 1) increased mRNA and protein expression of the three ENaC subunits (?, ? and ?) and serum- and glucocorticoid inducible kinase 1, as revealed by real-time RT-qPCR and immunoblotting analyses; 2) impaired Dot1a-AF9 interaction and H3 K79 methylation at the ?ENaC promoter without affecting AF9 binding to the promoter, as evidenced by chromatin immunoprecipitation; and 3) elevated ENaC-mediated Na(+) transport, as analyzed by measurement of benzamil-sensitive intracellular [Na(+)] and equivalent short circuit current using single-cell fluorescence imaging and an epithelial Volt-ohmmeter, respectively. Knockdown of AF17 elicited opposite effects. However, combination of AF17 overexpression or depletion with aldosterone treatment did not cause an additive effect on mRNA expression of the ENaC subunits. Taken together, we conclude that AF17 promotes Dot1a nuclear export and upregulates basal, but not aldosterone-stimulated ENaC expression, leading to an increase in ENaC-mediated Na(+) transport in renal collecting duct cells.
| S-EPMC3210795 | biostudies-literature
Project description:The kinetics of sodium-stimulated phosphate flux and phosphate-stimulated sodium flux in human red cells have been previously described (Shoemaker, D.G., C.A. Bender, and R.B. Gunn. 1988. J. Gen. Physiol. 92:449-474). However, despite the identification of multiple isoforms in three gene families (Timmer, R.T., and R.B. Gunn. 1998. Am. J. Physiol. Cell Physiol. 274:C757-C769), the molecular basis for the sodium-phosphate cotransporter in erythrocytes is unknown. Most cells express multiple isoforms, thus disallowing explication of isoform-specific kinetics and function. We have found that erythrocyte membranes express one dominant isoform, hBNP-1, to which the kinetics can thus be ascribed. In addition, because the erythrocyte Na-PO(4) cotransporter can also mediate Li-PO(4) cotransport, it has been suggested that this transporter functions as the erythrocyte Na-Li exchanger whose activity is systematically altered in patients with bipolar disease and patients with essential hypertension. To determine the molecular basis for the sodium-phosphate cotransporter, we reasoned that if the kinetics of phosphate transport in a nucleated erythroid-like cell paralleled those of the Na-activated pathway in anucleated erythrocytes and yet were distinct from those known for other Na-PO(4) cotransporters, then the expressed genes may be the same in both cell types. In this study, we show that the kinetics of sodium phosphate cotransport were similar in anuclear human erythrocytes and K562 cells, a human erythroleukemic cell line. Although the erythrocyte fluxes were 750-fold smaller, the half-activation concentrations for phosphate and sodium and the relative cation specificities for activation of (32)PO(4) influx were similar. Na-activation curves for both cell types showed cooperativity consistent with the reported stoichiometry of more than one Na cotransported per PO(4). In K562 cells, external lithium activation of phosphate influx was also cooperative. Inhibition by arsenate, K(I) = 2.6-2.7 mM, and relative inhibition by amiloride, amiloride analogs, phosphonoformate, and phloretin were similar. These characteristics were different from those reported for hNaPi-3 and hPiT-1 in other systems. PCR analysis of sodium-phosphate cotransporter isoforms in K562 cells demonstrated the presence of mRNAs for hPiT-1, hPiT-2, and hBNP-1. The mRNAs for hNaPi-10 and hNaPi-3, the other two known isoforms, were absent. Western analysis of erythrocytes and K562 cells with isoform-specific antibodies detected the presence of only hBNP-1, an isoform expressed in brain neurons and glia. The similarities in the kinetics and the expression of only hBNP-1 protein in the two cell types is strong evidence that hBNP-1 is the erythrocyte and K562 cell sodium-phosphate cotransporter.
| S-EPMC2233690 | biostudies-literature