scholarly journals Characterization of l-carnitine transport by rat kidney brush-border-membrane vesicles

1995 ◽  
Vol 309 (2) ◽  
pp. 643-647 ◽  
Author(s):  
B Stieger ◽  
B O′Neill ◽  
S Krähenbühl
Keyword(s):  
Membrane Potential ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Rat Kidney ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Transport Systems ◽  
Renal Brush Border Membrane ◽  
Carnitine Transport

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.

Potential-dependent D-glucose uptake by renal brush border membrane vesicles in the absence of sodium

1982 ◽  
Vol 242 (4) ◽  
pp. F340-F345
Author(s):  
S. Hilden ◽  
B. Sacktor
Keyword(s):  
Membrane Potential ◽  
Glucose Uptake ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Transport Systems ◽  
Uptake System ◽  
Renal Brush Border Membrane ◽  
Renal Brush Border

The uptake of D-glucose by renal brush border membrane vesicles was studied in the absence of Na+. Uptake of the sugar was membrane potential dependent (inside negative), inhibited by phlorizin, sugar and stereospecific, accelerated by exchange diffusion, saturable, and temperature dependent. The binding of phlorizin in the absence of Na+ was also increased by a membrane potential (inside negative). Thus, the properties of this membrane potential-dependent, Na+-independent sugar transport system resembled those described for the Na+-D-glucose cotransport system. In the absence of Na+ but in the presence of a valinomycin-induced K+ diffusion potential the apparent Km for D-glucose was 43 mM. This contrasted with an apparent Km of 1.8 mM for the Na+ chemical gradient system. Therefore, the Na+-independent uptake system represented a low-affinity transport mechanism. It is suggested that the same carrier mediated the Na+-independent and Na+-dependent transport systems. A hypothetical model for the membrane potential-dependent stimulation of D-glucose uptake in the absence of Na+ is proposed.

scholarly journals Chloride and membrane potential dependence of sodium ion-proline symport.

1991 ◽  
Vol 2 (4) ◽  
pp. 885-893
Author(s):  
R W Chesney ◽  
I Zelikovic ◽  
A Budreau ◽  
D Randle
Keyword(s):  
Membrane Potential ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Initial Rate ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Transport Systems ◽  
Gamma Aminobutyric Acid ◽  
Renal Brush Border Membrane

Proline accumulation by renal proximal tubule brush border membrane vesicles is Na+ dependent, but little is known about the role of anions or membrane potential on proline uptake. Recent studies in a variety of transport systems, including rat renal brush border membrane vesicles, indicate that halide anions chloride (Cl-) and bromide (Br-) are essential for glycine, beta-alanine, gamma-aminobutyric acid, and taurine uptake, so the possibility that Na(+)-proline symport is Cl- dependent was explored. Also, the role of membrane potential on transport was assessed by determining the effect of external anions with different membrane permeabilities. The ratio of initial rate Cl- stimulated to thiocyanate (SCN)(-)-stimulated uptake values serves to measure Cl- dependence. The initial rate of proline uptake to equilibrium value was 3.11 +/- 0.5 (SE) in the presence of Cl- versus SCN-. The ratio for D-glucose, whose uptake is governed only by electrogenic status of the membrane, was 0.61 +/- 0.47 (P less than 0.001 versus proline). In another series of experiments, uptake values for various anions as a percent of equilibrium (I/E x 100) were: SCN-, 84.9 +/- 10.9; NO3, 49.9 +/- 11.0; SO4(2-), 27.3 +/- 4.4; F-, 68.5 +/- 18.3; Cl-, 164.1 +/- 44.6; Br-, 150.6 +/- 30.2; I-, 56.7 +/- 13.5. The stoichiometry of uptake by Hill plot analysis of proline uptake in the presence of varying concentrations of Na+ (0 to 100 mM) and Cl- (0 to 100 mM) was 2Na+:1Cl-:1 proline.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathways for carboxylic acid transport by rabbit renal brush border membrane vesicles

1982 ◽  
Vol 243 (5) ◽  
pp. F456-F462 ◽  
Author(s):  
E. Nord ◽  
S. H. Wright ◽  
I. Kippen ◽  
E. M. Wright
Keyword(s):  
Dicarboxylic Acid ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Transport Systems ◽  
Monocarboxylic Acids ◽  
Filtration Method ◽  
Polycarboxylic Acids ◽  
Renal Brush Border Membrane

Brush border membrane vesicles were purified from rabbit renal cortex using a calcium-precipitation procedure, and the uptake of carboxylic acids was determined by a rapid-filtration method. L-Lactate, pyruvate (monocarboxylic acids), and succinate (dicarboxylic acid) demonstrated features of Na+ cotransport: enhanced initial rate (1 s) of uptake with an inward Na+ gradient compared with the Na+ -free control condition and transient accumulation of substrate within the vesicles. Kinetic parameters derived for L-lactate and succinate show that each substrate is transported via single pathway and that the two substrates exhibit marginal cross-inhibition. A range of monocarboxylic acids including pyruvate and ketone bodies appear to interact with the monocarboxylic acid carrier. The kinetics of Nat-dependent pyruvate uptake suggest at least two transport pathways-namely, that this monocarboxylate shares both the mono- and dicarboxylic acid carriers. We conclude that isolated rabbit renal microvillus membranes possess independent transport systems for mono- and polycarboxylic acids.

Characterization of organic cation transport by avian renal brush-border membrane vesicles

1995 ◽  
Vol 269 (5) ◽  
pp. R1050-R1059 ◽  
Author(s):  
A. R. Villalobos ◽  
E. J. Braun
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Organic Cation ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Organic Cations ◽  
Michaelis Constant ◽  
Renal Brush Border Membrane ◽  
Avian Kidney

Organic cations are actively secreted by the renal proximal tubule. Studies on perfused tubules and isolated membranes from mammals and reptiles have demonstrated that organic cations (OC) are transported across the luminal (brush-border) membrane by OC/H+ exchange. Our objective was to determine whether a similar mechanism was present in the avian kidney. Uptake of [14C]tetraethylammonium (TEA) was assayed under various ionic conditions by rapid filtration in brush-border membrane vesicles (BBMV) isolated from chicken kidney (Gallus domesticus). An outwardly directed proton gradient (pHin = 6.0: pHout = 7.5) stimulated concentrative TEA uptake. TEA/H+ exchange was saturable, having a maximal rate of uptake of approximately 25 nmol.mg protein-1.min-1 and a Michaelis constant for TEA of approximately 500 microM. TEA transport could be indirectly coupled to sodium transport. Unlabeled TEA, N'-methylnicotinamide (NMN), choline, cimetidine, mepiperphenidol, quinidine, quinine, and ranitidine markedly cis-inhibited uptake of [14C]TEA. However, the organic anions probenecid and p-aminohippurate poorly inhibited uptake. Unlabeled TEA and NMN also trans-stimulated [14C]TEA uptake. Thus, in avian renal BBMV, organic cations are transported by an OC/H+ exchange mechanism qualitatively similar to that present in mammals.

scholarly journals Multiple sodium-dependent nucleoside transport systems in bovine renal brush-border membrane vesicles

1991 ◽  
Vol 274 (1) ◽  
pp. 27-33 ◽  
Author(s):  
T C Williams ◽  
S M Jarvis
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Nucleoside Transport ◽  
Transport Systems ◽  
Facilitated Diffusion ◽  
Nucleoside Transporter ◽  
Renal Brush Border Membrane ◽  
Renal Brush Border

Na(+)-dependent nucleoside transport was examined in bovine renal brush-border membrane vesicles. Two separate Na+/nucleoside cotransporters were shown to be present: (1) a system specific for purine nucleosides and uridine, designated as the N1 carrier, and (2) an Na(+)-dependent nucleoside transporter that accepts pyrimidine nucleosides, adenosine and analogues of adenosine, designated as the N2 system. Both systems exhibit a high affinity for nucleosides (apparent Km values approximately 10 microM), are insensitive to inhibition by facilitated-diffusion nucleoside transport inhibitors, are rheogenic and exhibit a high specificity for Na+. Na+ increases the affinity of the influx of guanosine and thymidine, nucleosides that serve as model permeants for the N1 and N2 nucleoside transporters respectively. The Na+/nucleoside coupling stoichiometry is consistent with 1:1 for both carriers.

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