Facilitated diffusion of urate in avian brush-border membrane vesicles

2002 ◽  
Vol 283 (4) ◽  
pp. C1155-C1162 ◽  
Author(s):  
Steven M. Grassl
Keyword(s):  
Membrane Potential ◽  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Facilitated Diffusion ◽  
Transport Pathways ◽  
Proximal Tubule Cells ◽  
Avian Kidney

Membrane transport pathways mediating transcellular secretion of urate across the proximal tubule were investigated in brush-border membrane vesicles (BBMV) isolated from avian kidney. An inside-positive K diffusion potential induced a conductive uptake of urate to levels exceeding equilibrium. Protonophore-induced dissipation of membrane potential significantly reduced voltage-driven urate uptake. Conductive uptake of urate was inhibitor sensitive, substrate specific, and a saturable function of urate concentration. Urate uptake was trans-stimulated by urate and cis-inhibited by p-aminohippurate (PAH). Conductive uptake of PAH was cis-inhibited by urate. Urate uptake was unaffected by an outward α-ketoglutarate gradient. In the absence of a membrane potential, urate uptake was similar in the presence and absence of an imposed inside-alkaline pH gradient or an outward Cl gradient. These observations suggest a uniporter-mediated facilitated diffusion of urate as a pathway for passive efflux across the brush border membrane of urate-secreting proximal tubule cells.

Ca2+ transport pathways in brush-border membrane vesicles of crustacean antennal glands

1993 ◽  
Vol 264 (6) ◽  
pp. R1206-R1213 ◽  
Author(s):  
G. A. Ahearn ◽  
P. Franco
Keyword(s):  
Membrane Potential ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Carrier System ◽  
Transport Pathways ◽  
45Ca Uptake ◽  
Negative Membrane Potential ◽  
Antennal Glands

Calcium uptake by brush-border membrane vesicles of Atlantic lobster (Homarus americanus) kidneys (antennal glands) in independent experiments was stimulated by outwardly directed Na or H gradients. In the absence of external amiloride, 45Ca uptake was strongly stimulated by an outwardly directed Na gradient, and this stimulation was enhanced by the addition of an inside-negative membrane potential. External amiloride (2 mM) reduced 45Ca uptake sixfold and lowered sensitivity to membrane potential. 45Ca influx kinetics (2.5-s uptake) in the presence of an outwardly directed H gradient and inside-negative membrane potential were composed of three components: 1) an amiloride-sensitive carrier system, 2) an amiloride-insensitive carrier system, and 3) a verapamil- and membrane potential-sensitive process that may represent diffusional transfer through a calcium channel. It was concluded that 45Ca entry by the amiloride-sensitive process occurred by a previously described electrogenic 2 Na-1 H antiport mechanism [Ahearn, G., and L. Clay. Am. J. Physiol. 257 (Regulatory Integrative Comp. Physiol. 26): R484-R493, 1989; Am. J. Physiol. 259 (Renal Fluid Electrolyte Physiol. 28): F758-F767, 1990; Ahearn, G., P. Franco, and L. Clay. J. Membr. Biol. 116: 215-226, 1990]. 45Ca influx by the amiloride-insensitive mechanism occurred by an apparent electroneutral 1 Ca-2 Na exchange. Transport stoichiometry of the latter mechanism was tentatively established by experiments determining intravesicular Na binding properties and by its apparent lack of response to a membrane potential. At physiological Na, Ca, and H concentrations in the antennal gland lumen and epithelial cytosol, these three calcium transport pathways individually may make significant contributions to net calcium reabsorption to the blood.

Urate/α-ketoglutarate exchange in avian basolateral membrane vesicles

2002 ◽  
Vol 283 (4) ◽  
pp. C1144-C1154 ◽  
Author(s):  
Steven M. Grassl
Keyword(s):  
Proximal Tubule ◽  
Brush Border Membrane ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Basolateral Membrane Vesicles ◽  
Transport Pathways ◽  
Proximal Tubule Cells ◽  
Flux Measurements ◽  
Avian Kidney ◽  
Sufficient Magnitude

Membrane transport pathways for transcellular secretion of urate across the proximal tubule were investigated in avian kidney. The presence of coupled urate/α-ketoglutarate exchange was investigated in basolateral membrane vesicles (BLMV) by [14C]urate and [α-3H]ketoglutarate flux measurements. An inward Na gradient induced accumulation of α-ketoglutarate of sufficient magnitude to suggest a Na-dicarboxylate cotransporter. An inward Na gradient also induced concentrative accumulation of urate in the presence of α-ketoglutarate but not in its absence, suggesting urate/α-ketoglutarate exchange. α-Ketoglutarate-dependent stimulation of urate uptake was not observed in brush-border membrane vesicles. An outward urate gradient induced concentrative accumulation of α-ketoglutarate. α-Ketoglutarate-coupled urate uptake was specific for α-ketoglutarate, Cl dependent, and insensitive to membrane potential. α-Ketoglutarate-coupled urate uptake was inhibited by increasing p-aminohippurate (PAH) concentrations, and α-ketoglutarate-coupled PAH uptake was observed. α-Ketoglutarate-coupled PAH uptake was inhibited by increasing urate concentrations, and an outward urate gradient induced concentrative accumulation of PAH. These results suggest a Cl-dependent, α-ketoglutarate-coupled anion exchange mechanism as a pathway for active urate uptake across the basolateral membrane of urate-secreting proximal tubule cells.

Nicotinic acid transport by brush border membrane vesicles from rabbit kidney

1981 ◽  
Vol 240 (3) ◽  
pp. F185-F191 ◽  
Author(s):  
E. F. Boumendil-Podevin ◽  
R. A. Podevin
Keyword(s):  
Membrane Potential ◽  
Nicotinic Acid ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Isonicotinic Acid ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Rabbit Kidney ◽  
Internal Space ◽  
Acid Uptake

The transport of nicotinic acid was investigated in brush border membrane vesicles isolated from rabbit kidney. The imposition of a Na+ gradient (out to in) induced a transient stimulation of nicotinic acid uptake above its final equilibrium value. This stimulation was specific for Na+. The uptake of nicotinic acid by the brush border membranes represented transport into an internal space and occurred in the absence of significant nicotinic acid degradation. The Na+ gradient-dependent uptake of nicotinic acid was saturable, apparent Km = 0.3 mM. Uptake of nicotinic acid was inhibited by its two isomers: picolinic and isonicotinic acid. In contrast, pyridine derivatives with two carboxyl groups or an amide group in addition to the carboxyl group were without inhibitory effect. Evaluation of changes in membrane potential using the lipophilic cation triphenylmethylphosphonium demonstrated that conditions that transiently generated either an interior-positive or an interior-negative membrane potential failed to affect the Na+-dependent transport of nicotinic acid. These findings provide evidence of the existence on the luminal membrane of a Na+ gradient-dependent and electroneutral transport system for nicotinic acid.

Ionic permeabilities of rat renal cortical brush-border membrane vesicles

1987 ◽  
Vol 252 (4) ◽  
pp. F700-F711
Author(s):  
M. S. Lipkowitz ◽  
R. G. Abramson
Keyword(s):  
Membrane Potential ◽  
Glucose Uptake ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Electrolyte Concentration ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Prolonged Incubation ◽  
New Methods ◽  
Electrochemical Equilibrium

It is generally assumed that electrolytes equilibrate readily across renal cortical brush-border membrane vesicles (BBMV). This assumption was tested by use of two new methods in rat BBMV prepared with free-flow electrophoresis (FFE), Mg aggregation, or Ca aggregation. Intravesicular KCl and RbCl concentrations, as well as the conductance of Cl relative to K (GCl/GK) and GNa/GK were determined with the fluorescent, potential-sensitive probe 3,3'-dipropylthiadicarbocyanine iodide [diS-C3-(5)]; intravesicular KCl concentration was also approximated utilizing the response of Na-dependent [3H]glucose uptake to variations in the membrane potential. These studies demonstrated that KCl fails to attain electrochemical equilibrium in BBMV prepared by the three methods, despite prolonged incubation at 22 degrees C; a significant, inwardly directed electrolyte gradient was sustained in all cases. The intravesicular electrolyte concentration was lower in BBMV prepared with FFE than in those prepared with Mg or Ca. GCl/GK was lowest in BBMV prepared with FFE and highest in those prepared with Ca; GNa/GK was comparable in all preparations. The apparent impermeance of BBMV may impact significantly in interpreting data from studies that require knowledge of the precise concentration of intravesicular electrolytes.

scholarly journals The Escherichia coli Enterotoxin STb Permeabilizes Piglet Jejunal Brush Border Membrane Vesicles

2007 ◽  
Vol 75 (5) ◽  
pp. 2208-2213 ◽  
Author(s):  
Carina Gonçalves ◽  
Vincent Vachon ◽  
Jean-Louis Schwartz ◽  
J. Daniel Dubreuil
Keyword(s):  
Escherichia Coli ◽  
Membrane Potential ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Ionic Selectivity ◽  
Intact Membrane ◽  
Target Membrane ◽  
First Time

ABSTRACT The membrane-permeabilizing ability of the Escherichia coli enterotoxin STb was evaluated using brush border membrane vesicles isolated from piglet jejunum and a membrane-potential-sensitive fluorescent probe, 3,3′-dipropylthiadicarbocyanine iodide. A strong membrane potential was generated by the efflux of K+ ions from the vesicles in the presence of the potassium ionophore valinomycin. Under these conditions, preincubation of the vesicles with STb efficiently depolarized the membrane in a dose-dependent and saturable manner. This activity was independent of pH, however, at least between pH 5.5 and 8.0. On the other hand, in the absence of valinomycin, STb had no significant influence on the measured fluorescence levels, indicating that it was unable to modify the ionic selectivity of the intact membrane. In agreement with the fact that the integrity of the disulfide bridges of STb is known to be essential for its biological activity, a reduced and alkylated form of the toxin was unable to depolarize the membrane in the presence of valinomycin. Furthermore, two previously described poorly active STb mutants, M42S and K22A-K23A, showed no membrane-permeabilizing capacity. These results demonstrate for the first time that STb can permeabilize its target membrane and suggest that it does so by forming nonspecific pores.

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