Urate transport in the proximal tubule: in vivo and vesicle studies

1985 ◽  
Vol 249 (6) ◽  
pp. F789-F798 ◽  
Author(s):  
A. M. Kahn ◽  
E. J. Weinman
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Anion Exchanger ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Transport Processes ◽  
Basolateral Membrane Vesicles ◽  
Urate Transport ◽  
Rat Proximal Tubule

The transport of urate in the mammalian nephron is largely confined to the proximal tubule. Depending on the species, net reabsorption or net secretion is observed. The rat, like the human and the mongrel dog, demonstrates net reabsorption of urate and has been the most extensively studied species. The unidirectional reabsorption and secretion of urate in the rat proximal tubule occur via a passive and presumably paracellular route and by a mediated transcellular route. The reabsorption of urate, and possibly its secretion, can occur against an electrochemical gradient. A variety of drugs and other compounds affect the reabsorption and secretion of urate. The effects of these agents depend on their site of application (luminal or blood), concentration, and occasionally their participation in transport processes that do not have affinity for urate. Recent studies with renal brush border and basolateral membrane vesicles from the rat and brush border vesicles from the dog have determined the mechanisms for urate transport across the luminal and antiluminal membranes of the proximal tubule cell. Brush border membrane vesicles contain an anion exchanger with affinity for urate, hydroxyl ion, bicarbonate, chloride, lactate, p-aminohippurate (PAH), and a variety of other organic anions. Basolateral membrane vesicles contain an anion exchanger with affinity for urate and chloride but not for PAH. Both membrane vesicle preparations also permit urate translocation by simple diffusion. A model for the transcellular reabsorption and secretion of urate in the rat proximal tubule is proposed. This model is based on the vesicle studies, and it can potentially explain the majority of urate transport data obtained with in vivo techniques.

Na+ gradient-dependent glycine uptake in basolateral membrane vesicles from the dog kidney

1985 ◽  
Vol 249 (3) ◽  
pp. F338-F345
Author(s):  
S. J. Schwab ◽  
M. R. Hammerman
Keyword(s):  
Amino Acids ◽  
Membrane Potential ◽  
Brush Border ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Transport Processes ◽  
Basolateral Membrane Vesicles ◽  
Glycine Uptake ◽  
Dog Kidney ◽  
Dependent Transport

The imposition of a Na+ gradient (extravesicular greater than intravesicular) stimulated the uptake of [3H]glycine measured over time in basolateral membrane vesicles from dog kidney over that measured in the presence of a choline+ gradient or measured under Na+-equilibrated conditions. Na+ gradient-dependent uptake of [3H]glycine was stimulated by an intravesicular-negative membrane potential. Efflux of [3H]glycine was enhanced by an intravesicular-positive membrane potential. Substrate velocity analysis of net Na+-dependent [3H]glycine uptake over the range of amino acid concentrations from 10 to 500 microM demonstrated a single saturable transport system with apparent Km = 84 microM and apparent Vmax = 143 pmol [3H]glycine X mg protein-1 X 15 s-1. Counterflow of [3H]glycine was demonstrated in the presence of Na+ when basolateral vesicles were preloaded with glycine but not with L-alanine or L-proline. These findings are consistent with carrier-mediated, electrogenic cotransport of Na+ and glycine in basolateral vesicles. Unlike the case for [3H]glycine, Na+ gradient-dependent uptake of neither L-[3H]alanine nor L-[3H]proline was observed in basolateral vesicles. Na+ gradient-dependent uptake of all three amino acids was demonstrated in brush border vesicles from the dog kidney. We conclude that variability exists between basolateral and brush border membranes in terms of the presence or absence of Na+-dependent transport systems for specific amino acids. This variability probably reflects differences between the functional significances of the Na+-dependent transport processes in the two membranes.

Carrier-mediated concentrative urate transport in rat renal membrane vesicles

1985 ◽  
Vol 248 (4) ◽  
pp. F574-F584 ◽  
Author(s):  
R. G. Abramson ◽  
M. S. Lipkowitz
Keyword(s):  
Chemical Equilibrium ◽  
Brush Border ◽  
Anion Exchanger ◽  
Driving Force ◽  
Renal Cortex ◽  
Copper Chloride ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Basolateral Membrane Vesicles ◽  
The Media

[2-14C]Urate uptake and efflux were studied in brush border and basolateral membrane vesicles of rat renal cortex that were exposed to 20 microM copper chloride. In the presence of inwardly directed NaCl gradients urate uptake was maintained at levels in excess of chemical equilibrium. Comparison of glucose and chloride uptakes revealed that equilibrium glucose uptake was not affected by copper, but chloride failed to reach equilibrium in copper-exposed vesicles. It is suggested that the persistence of an electrolyte gradient could provide a driving force to raise the concentration of free intravesicular urate above that in the media. Preincubation of vesicles with unlabeled urate failed to diminish uptake of added urate; rather, urate uptake was trans stimulated. Uptake of labeled urate was also significantly accelerated when an outward gradient for unlabeled urate was created. Pyrazinoic and oxonic acids also trans stimulated urate uptake. The demonstration of accelerated homeo- and heteroexchange diffusion indicates that transport is carrier mediated in both brush border and basolateral vesicles. Outwardly directed hydroxyl gradients failed to influence urate uptake in either the presence or absence of copper or NaCl. Thus, this carrier, which is active only in the presence of trace amounts of copper, is distinct from a urate/anion exchanger.

Indirect Na+ dependency of urate and p-aminohippurate transport in pig basolateral membrane vesicles

1991 ◽  
Vol 261 (2) ◽  
pp. F265-F272 ◽  
Author(s):  
D. Werner ◽  
F. Roch-Ramel
Keyword(s):  
Proximal Tubule ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Organic Anions ◽  
Transport Processes ◽  
Basolateral Membrane Vesicles ◽  
Pig Kidney ◽  
Different Characteristics ◽  
Stimulation Of

Membrane vesicles were used to study the basolateral transport of urate and p-aminohippurate (PAH) in the proximal tubule of the pig kidney. Consistent with a cooperation between a Na(+)-2-oxoglutarate cotransporter and a 2-oxoglutarate-urate or a 2-oxoglutarate-PAH exchanger, urate and PAH uptakes were stimulated in presence of extravesicular 2-oxoglutarate when an inwardly directed Na+ gradient was applied. Both transports exhibited, however, different characteristics. The optimal 2-oxoglutarate concentration for stimulating uptakes was 10 microM for PAH and 150 microM for urate. Extravesicular chloride was required to observe a stimulation of PAH uptake but not of urate uptake. Transports of both PAH and urate exhibited different affinity sequences for various organic anions. Stimulated PAH uptake was inhibited by probenecid greater than cold PAH greater than urate = pyrazinoate greater than lactate, whereas stimulated urate uptake was inhibited by probenecid greater than cold urate greater than PAH and not by pyrazinoate or lactate. These results are consistent with independent transport processes for urate and PAH in pig basolateral membrane vesicles, both being indirectly driven by an inwardly directed Na+ gradient.

scholarly journals Characterization of sodium-dependent and sodium-independent nucleoside transport systems in rabbit brush-border and basolateral plasma-membrane vesicles from the renal outer cortex

1989 ◽  
Vol 264 (1) ◽  
pp. 223-231 ◽  
Author(s):  
T C Williams ◽  
A J Doherty ◽  
D A Griffith ◽  
S M Jarvis
Keyword(s):  
Brush Border ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Nucleoside Transport ◽  
Transport Systems ◽  
Facilitated Diffusion ◽  
Basolateral Membrane Vesicles ◽  
Plasma Membrane Vesicles ◽  
Outer Cortex ◽  
Overshoot Phenomenon

The transport of uridine into rabbit renal outer-cortical brush-border and basolateral membrane vesicles was compared at 22 degrees C. Uridine was taken up into an osmotically active space in the absence of metabolism for both types of membrane vesicles. Uridine influx by brush-border membrane vesicles was stimulated by Na+, and in the presence of inwardly directed gradients of Na+ a transient overshoot phenomenon was observed, indicating active transport. Kinetic analysis of the saturable Na+-dependent component of uridine flux indicated that it was consistent with Michaelis-Menten kinetics (Km 12 +/- 3 microM, Vmax. 3.9 +/- 0.9 pmol/s per mg of protein). The sodium:uridine coupling stoichiometry was found to be consistent with 1:1 and involved the net transfer of positive charge. In contrast, uridine influx by basolateral membrane vesicles was not dependent on the cation present and was inhibited by nitrobenzylthioinosine (NBMPR). NBMPR-sensitive uridine transport was saturable (Km 137 +/- 20 microM, Vmax. 5.2 +/- 0.6 pmol/s per mg of protein). Inhibition of uridine flux by NBMPR was associated with high-affinity binding of NBMPR to the basolateral membrane (Kd 0.74 +/- 0.46 nM). Binding of NBMPR to these sites was competitively blocked by adenosine and uridine. These results indicate that uridine crosses the brush-border surface of rabbit proximal renal tubule cells by Na+-dependent pathways, but permeates the basolateral surface by NBMPR-sensitive facilitated-diffusion carriers.

Na+-independent D-glucose transport in rabbit renal basolateral membranes

1988 ◽  
Vol 254 (5) ◽  
pp. F711-F718 ◽  
Author(s):  
P. T. Cheung ◽  
M. R. Hammerman
Keyword(s):  
Glucose Uptake ◽  
Glucose Transport ◽  
Brush Border ◽  
Glucose Transporter ◽  
Cytochalasin B ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Rabbit Kidney ◽  
Basolateral Membrane Vesicles ◽  
Proximal Tubular

To define the mechanism by which glucose is transported across the basolateral membrane of the renal proximal tubular cell, we measured D-[14C]glucose uptake in basolateral membrane vesicles from rabbit kidney. Na+-dependent D-glucose transport, demonstrable in brush-border vesicles, could not be demonstrated in basolateral membrane vesicles. In the absence of Na+, the uptake of D-[14C]glucose in basolateral vesicles was more rapid than that of L-[3H]glucose over a concentration range of 1-50 mM. Subtraction of the latter from the former uptakes revealed a saturable process with apparent Km of 9.9 mM and Vmax of 0.80 nmol.mg protein-1.s-1. To characterize the transport component of D-glucose uptake in basolateral vesicles, we measured trans stimulation of 2 mM D-[14C]glucose entry in the absence of Na+. Trans stimulation could be effected by preloading basolateral vesicles with D-glucose, 2-deoxy-D-glucose, or 3-O-methyl-D-glucose, but not with L-glucose or alpha-methyl-D-glucoside. Trans-stimulated D-[14C]glucose uptake was inhibited by 0.1 mM phloretin or cytochalasin B but not phlorizin. In contrast, Na+-dependent D-[14C]glucose transport in brush-border vesicles was inhibited by phlorizin but not phloretin or cytochalasin B. Our findings are consistent with the presence of a Na+-independent D-glucose transporter in the proximal tubular basolateral membrane with characteristics similar to those of transporters present in nonepithelial cells.

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