Dietary Acid and Alkali Loading Do Not Alter Taurine Uptake by Renal Proximal Tubule Brush Border Membrane Vesicles in Kittens

1991 ◽  
Vol 121 (2) ◽  
pp. 215-222 ◽  
Author(s):  
Taesun Park ◽  
Quinton R. Rogers ◽  
James G. Morris ◽  
James P. G. Morris
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Renal Proximal Tubule ◽  
Brush Border Membrane Vesicles ◽  
Dietary Acid ◽  
Taurine Uptake

Characteristics of the Na+-H+ antiporter in the intact renal proximal tubular cell

1986 ◽  
Vol 250 (3) ◽  
pp. F539-F550 ◽  
Author(s):  
E. P. Nord ◽  
D. Goldfarb ◽  
N. Mikhail ◽  
P. Moradeshagi ◽  
A. Hafezi ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Intact Cell ◽  
Membrane Vesicles ◽  
Renal Proximal Tubule ◽  
Brush Border Membrane Vesicles ◽  
Intact Cells ◽  
Proximal Tubular ◽  
Internal Site

The characteristics of the proximal tubular Na+-H+ antiporter were determined in isolated proximal tubular cells to ascertain whether the features of this transport system in intact cells are comparable with those previously described for isolated brush-border membrane vesicles. A method is described for the rapid isolation of a purified preparation of cells that demonstrate morphological and functional characteristics of the renal proximal tubule. The cells maintain their polarity while in suspension, and adenylate cyclase activity is enhanced by parathyroid hormone but not by arginine vasopressin. The cells display gluconeogenic function and Na+-dependent alpha-methyl-D-glucose and organic phosphate cotransport, processes that confirm their proximal tubule origin. O2 consumption rates and cytosolic adenosine triphosphate levels indicate functional integrity. Na+-H+ antiport activity was defined in these cells by measuring amiloride-sensitive Na+ uptake. At intracellular pH = 6.4 vs. extracellular pH = 7.4, KtNa was 10.1 +/- 2.8 mM, and maximal sodium flux was 0.89 +/- 0.13 nmol X 10(6) cells-1 X K0.5 for amiloride and ethyl-isopropyl amiloride, measured at an external Na+ concentration of 1 mM, was observed at 2.5 X 10(-5) M and 2.9 X 10(-6) M, respectively. The external and internal loci of the exchanger displayed asymmetric affinity for the hydrogen ion: the apparent pK for the external site was 7.20-7.26 vs. less than 6.5 for the internal site. The internal site demonstrated features of positive cooperativity. In summary, the Na+-H+ antiporter present in the luminal membrane of the renal proximal tubule has been characterized in the intact cell and displays functional and kinetic parameters closely resembling those described in isolated brush-border membrane vesicles.

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.

Ischemic injury induces ADF relocalization to the apical domain of rat proximal tubule cells

2001 ◽  
Vol 280 (5) ◽  
pp. F886-F894 ◽  
Author(s):  
Sharon L. Ashworth ◽  
Ruben M. Sandoval ◽  
Melanie Hosford ◽  
James R. Bamburg ◽  
Bruce A. Molitoris
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Apical Membrane ◽  
Critical Role ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Actin Binding ◽  
Proximal Tubule Cell ◽  
Apical Domain

Breakdown of proximal tubule cell apical membrane microvilli is an early-occurring hallmark of ischemic acute renal failure. Intracellular mechanisms responsible for these apical membrane changes remain unknown, but it is known that actin cytoskeleton alterations play a critical role in this cellular process. Our laboratory previously demonstrated that ischemia-induced cell injury resulted in dephosphorylation and activation of the actin-binding protein, actin depolymerizing factor [(ADF); Schwartz, N, Hosford M, Sandoval RM, Wagner MC, Atkinson SJ, Bamburg J, and Molitoris BA. Am J Physiol Renal Fluid Electrolyte Physiol 276: F544–F551, 1999]. Therefore, we postulated that ischemia-induced ADF relocalization from the cytoplasm to the apical microvillar microfilament core was an early event occurring before F-actin alterations. To directly investigate this hypothesis, we examined the intracellular localization of ADF in ischemic rat cortical tissues by immunofluorescence and quantified the concentration of ADF in brush-border membrane vesicles prepared from ischemic rat kidneys by using Western blot techniques. Within 5 min of the induction of ischemia, ADF relocalized to the apical membrane region. The length of ischemia correlated with the time-related increase in ADF in isolated brush-border membrane vesicles. Finally, depolymerization of microvillar F-actin to G-actin was documented by using colocalization studies for G- and F-actin. Collectively, these data indicate that ischemia induces ADF activation and relocalization to the apical domain before microvillar destruction. These data further suggest that ADF plays a critical role in microvillar microfilament destruction and apical membrane damage during ischemia.

Sulphate and phosphate transport in the renal proximal tubule

1982 ◽  
Vol 299 (1097) ◽  
pp. 549-558 ◽  
Keyword(s):  
Cell Membrane ◽  
Proximal Tubule ◽  
Brush Border ◽  
Inorganic Phosphate ◽  
Brush Border Membrane ◽  
Ph Dependence ◽  
Membrane Vesicles ◽  
Dicarboxylic Acids ◽  
Phosphate Transport ◽  
Brush Border Membrane Vesicles

Experiments performed on microperfused proximal tubules and brush-border membrane vesicles revealed that inorganic phosphate is actively reabsorbed in the proximal tubule involving a 2 Na + -HPO 2- 4 or H 2 PO 4 - co-transport step in the brush-border membrane and a sodium-independent exit step in the basolateral cell membrane. Na + - phosphate co-transport is competitively inhibited by arsenate. The transtubular transport regulation is mirrored by the brush-border transport step: it is inhibited by parathyroid hormone intracellularly mediated by cyclic AMP. Transepithelial inorganic phosphate (P i ) transport and Na + -dependent P i transport across the brush-border membrane correlates inversely with the P i content of the diet. Intraluminal acidification as well as intracellular alkalinization led to a reduction of transepithelial P i transport. Data from brush-border membrane vesicles indicate that high luminal H + concentrations reduce the affinity for Na + of the Na + -phosphate co-transport system, and that this mechanism might be responsible for the pH dependence of phosphate reabsorption. Contraluminal influx of P i from the interstitium into the cell could be partly inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). It is not, however, changed when dicarboxylic acids are present or when the pH of the perfusate is reduced to pH 6. Sulphate is actively reabsorbed, involving electroneutral 2 Na + -SO 2 - 4 co-transport through the brush-border membrane. This transport step is inhibited by thiosulphate and molybdate, but not by phosphate or tungstate. The transtubular active sulphate reabsorption is not pH dependent, but is diminished by the absence of bicarbonate. The transport of sulphate through the contraluminal cell side is inhibited by DIDS and diminished when the capillary perfusate contains no bicarbonate or chloride. The latter data indicate the presence of an anion exchange system in the contraluminal cell membrane like that in the erythrocyte membrane.

Active transport of taurine in rabbit jejunal brush-border membrane vesicles

1989 ◽  
Vol 257 (1) ◽  
pp. G65-G72 ◽  
Author(s):  
Y. Miyamoto ◽  
C. Tiruppathi ◽  
V. Ganapathy ◽  
F. H. Leibach
Keyword(s):  
Amino Acids ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Uptake System ◽  
Absolute Requirement ◽  
Uptake Process ◽  
Transport Inhibitors ◽  
Taurine Uptake

The characteristics of taurine uptake in rabbit jejunal brush-border membrane vesicles were investigated. Taurine was transiently accumulated inside the vesicles against a concentration gradient when an inwardly directed NaCl gradient was imposed across the membrane. Uptake of taurine showed an absolute requirement for both Na+ and Cl-. The NaCl gradient-dependent taurine uptake was stimulated by a valinomycin-induced, inside-negative, K+-diffusion potential, suggesting that the uptake process was electrogenic. The uptake system exclusively interacted with beta-amino acids of small size, but had no affinity for alpha-amino acids. Kinetic analysis revealed that the system exhibited high affinity for taurine (Kt = 14.4 +/- 0.5 microM). Taurine uptake was greatly influenced by extravesicular concentrations of Na+ and Cl-. The Cl- stoichiometry was found to be one. In the presence of Cl-, taurine uptake was sigmoidally related to Na+ concentration, and the Na+ stoichiometry was calculated to be three. Thus three Na+ and one Cl- were involved per transport of one taurine molecule. The uptake process was not affected by other transport inhibitors such as amiloride, harmaline, furosemide, and 4,4'-diisothiocyanostilbene-2,2'-disulfonate.

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