scholarly journals Na(+)- and H(+)-gradient-dependent transport of alpha-aminoisobutyrate by luminal membrane vesicles from rabbit proximal tubule.

1991 ◽  
Vol 436 (1) ◽  
pp. 149-167 ◽  
Author(s):  
H Jessen ◽  
H Vorum ◽  
K E Jørgensen ◽  
M I Sheikh
Keyword(s):  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Luminal Membrane ◽  
Dependent Transport

scholarly journals l-tryptophan uptake by segment-specific membrane vesicles from the proximal tubule of rabbit kidney

1992 ◽  
Vol 286 (1) ◽  
pp. 103-110 ◽  
Author(s):  
H Jessen ◽  
M I Sheikh
Keyword(s):  
Proximal Tubule ◽  
Basolateral Membrane ◽  
Membrane Vesicles ◽  
Rabbit Kidney ◽  
Basolateral Membrane Vesicles ◽  
Luminal Membrane ◽  
Transport Component ◽  
Pars Recta ◽  
Dependent Transport ◽  
Pars Convoluta

1. The mechanism of the renal transport of L-tryptophan by basolateral and luminal membrane vesicles prepared from either the pars convoluta or the pars recta of the rabbit proximal tubule was studied. The uptake of L-tryptophan by basolateral membrane vesicles from the pars convoluta was found to be an Na(+)-dependent transport event. The Na(+)-conditional influx of the amino acid was stimulated in the presence of an inwardly directed H+ gradient. Lowering the pH without an H+ gradient had no effect, indicating that L-tryptophan is co-transported with H+. 3. On the other hand, no transient accumulation of L-tryptophan was observed in the presence or absence of Na+ in basolateral membrane vesicles from the pars recta. 4. In luminal membrane vesicles from the pars recta, the transient Na(+)-dependent accumulation of L-tryptophan occurred via a dual transport system. In addition, an inwardly directed H+ gradient could drive the uphill transport of L-tryptophan into these vesicles in both the presence and the absence of an Na+ gradient. 5. By contrast, the uptake of L-tryptophan by luminal membrane vesicles from the pars convoluta was a strictly Na(+)-dependent and electrogenic transport process, mediated by a single transport component. 6. Investigation of the coupling ratio in luminal membrane vesicles suggested that 1 Na+:1 L-tryptophan are co-transported in the pars convoluta. In the pars recta, examination of the stoichiometry indicated that approx. 1 H+ and 2 Na+ (high affinity) or 1 Na+ (low affinity) are involved in the uptake of L-tryptophan.

NHE3 activity and trafficking depend on the state of actin organization in proximal tubule

2001 ◽  
Vol 280 (2) ◽  
pp. F283-F290 ◽  
Author(s):  
C. Chalumeau ◽  
D. Du Cheyron ◽  
N. Defontaine ◽  
O. Kellermann ◽  
M. Paillard ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Cortical Cell ◽  
Membrane Vesicles ◽  
Cytochalasin D ◽  
The State ◽  
Protein Abundance ◽  
Transport Activity ◽  
Cortical Cells ◽  
Actin Organization ◽  
Luminal Membrane

The present study was addressed to define the contribution of cytoskeleton elements in the kidney proximal tubule Na+/H+ exchanger 3 (NHE3) activity under basal conditions. We used luminal membrane vesicles (LMV) isolated from suspensions of rat cortical tubules pretreated with either colchicine (Colch) or cytochalasin D (Cyto D). Colch pretreatment of suspensions (200 μM for 60 min) moderately decreased LMV NHE3 activity. Cyto D pretreatment (1 μM for 60 min) elicited an increase in LMV NHE3 transport activity but did not increase Na-glucose cotransport activity. Cyto D pretreatment of suspensions did not change the apparent affinity of NHE3 for internal H+. In contrast, after Cyto D pretreatment of the suspensions, NHE3 protein abundance was increased in LMV and remained unchanged in cortical cell homogenates. The effect of Cyto D on NHE3 was further assessed with cultures of murine cortical cells. The amount of surface biotinylated NHE3 increased on Cyto D treatment, whereas NHE3 protein abundance was unchanged in cell homogenates. In conclusion, under basal conditions NHE3 activity depends on the state of actin organization possibly involved in trafficking processes between luminal membrane and intracellular compartment.

scholarly journals A kinetically defined Na+/H+ antiporter within a mathematical model of the rat proximal tubule.

1995 ◽  
Vol 105 (5) ◽  
pp. 617-641 ◽  
Author(s):  
A M Weinstein
Keyword(s):  
Kinetic Model ◽  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Model Calculations ◽  
Kinetic Formulation ◽  
Luminal Membrane ◽  
Least Squares Fit ◽  
Velocity Effect ◽  
Rat Proximal Tubule

The luminal membrane antiporter of the proximal tubule has been represented using the kinetic formulation of E. Heinz (1978. Mechanics and Engergetics of Biological Transport. Springer-Verlag, Berlin) with the assumption of equilibrium binding and 1:1 stoichiometry. Competitive binding and transport of NH+4 is included within this model. Ion affinities and permeation velocities were selected in a least-squares fit to the kinetic parameters determined experimentally in renal membrane vesicles (Aronson, P.S., M.A. Suhm, and J. Nee. 1983. Journal of Biological Chemistry. 258:6767-6771). The modifier role of internal H+ to enhance transport beyond the expected kinetics (Aronson, P.S., J. Nee, and M. A. Suhm. 1982. Nature. 299:161-163) is represented as a velocity effect of H+ binding to a single site. This kinetic formulation of the Na+/H+ antiporter was incorporated within a model of the rat proximal tubule (Weinstein, A. M. 1994. American Journal of Physiology. 267:F237-F248) as a replacement for the representation by linear nonequilibrium thermodynamics (NET). The membrane density of the antiporter was selected to yield agreement with the rate of tubular Na+ reabsorption. Simulation of 0.5 cm of tubule predicts that the activity of the Na+/H+ antiporter is the most important force for active secretion of ammonia. Model calculations of metabolic acid-base disturbances are performed and comparison is made among antiporter representations (kinetic model, kinetic model without internal modifier, and NET formulation). It is found that the ability to sharply turn off Na+/H+ exchange in cellular alkalosis substantially eliminates the cell volume increase associated with high HCO3- conditions. In the tubule model, diminished Na+/H+ exchange in alkalosis blunts the axial decrease in luminal HCO3- and thus diminishes paracellular reabsorption of Cl-. In this way, the kinetics of the Na+/H+ antiporter could act to enhance distal delivery of Na+, Cl-, and HCO3- in acute metabolic alkalosis.

Axial heterogeneity of apical water permeability along rabbit kidney proximal tubule

1991 ◽  
Vol 260 (1) ◽  
pp. R186-R191 ◽  
Author(s):  
F. Van Der Goot ◽  
B. Corman
Keyword(s):  
Light Scattering ◽  
Proximal Tubule ◽  
Water Permeability ◽  
Membrane Surface ◽  
Morphological Difference ◽  
Membrane Vesicles ◽  
Rabbit Kidney ◽  
Elastic Light Scattering ◽  
Membrane Area ◽  
Luminal Membrane

In the rabbit nephron, the luminal membrane surface area of the proximal convoluted tubule (PCT) is more than twice that of the proximal straight tubule (PST). What seemed to be an increase in histological specialization in solute and water transport is curiously reflected by a lower transepithelial water permeability per unit of apical membrane area in PCT than in PST. To evaluate what change in luminal membrane water permeability corresponds to this morphological difference, the osmotic permeabilities (Pf) of brush-border membrane vesicles isolated from PCT and PST of rabbit kidney were compared. D-Glucose uptake rates indicated proper separation of two populations of vesicles. Vesicle size measured by quasi-elastic light scattering was 123 +/- 7 nm and 125 +/- 6 nm for vesicles isolated from PCT and PST, respectively. Pf obtained by stop-flow light scattering techniques was of 106 +/- 6 microns/s in PCT vesicles and 191 +/- 7 microns/s in PST vesicles (T = 26 degrees C). In the presence of the sulfhydryl reagent HgCl2, the water permeabilities of both types of membrane dropped to comparable values. These data, which show an 80% increase in apical water permeability along the length of the proximal tubule, suggest that the number of proteic water channels per unit of membrane area is greater in PST than in PCT.

Electrogenic uptake of d-imino acids by luminal membrane vesicles from rabbit kidney proximal tubule

1989 ◽  
Vol 984 (2) ◽  
pp. 231-237 ◽  
Author(s):  
Hans Røigaard-Petersen ◽  
Christian Jacobsen ◽  
Henrik Jessen ◽  
Steen Mollerup ◽  
M. Iqbal Sheikh
Keyword(s):  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Rabbit Kidney ◽  
Kidney Proximal Tubule ◽  
Luminal Membrane ◽  
Imino Acids
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