scholarly journals Developmental changes in rabbit proximal straight tubule paracellular permeability

2002 ◽  
Vol 283 (3) ◽  
pp. F525-F531 ◽  
Author(s):  
Raymond Quigley ◽  
Michel Baum
Keyword(s):  
Proximal Tubule ◽  
Chloride Transport ◽  
Chloride Concentration ◽  
Chloride Ions ◽  
Proximal Tubules ◽  
Chloride Permeability ◽  
Proximal Straight Tubule ◽  
Nephron Segment ◽  
Proximal Tubular

The early proximal tubule preferentially reabsorbs organic solutes and bicarbonate over chloride ions, resulting in a luminal fluid with a higher chloride concentration than that in blood. From this late proximal tubular fluid, one-half of NaCl reabsorption by the adult proximal tubule is active and transcellular and one-half is passive and paracellular. The purpose of the present in vitro microperfusion study was to determine the characteristics of passive chloride transport and permeability properties of the adult and neonatal proximal straight tubules (PST). In tubules perfused with a late proximal tubular fluid, net passive chloride flux was 131.7 ± 37.7 pmol · mm−1 · min−1in adult tubules and −17.1 ± 23.3 pmol · mm−1 · min−1 in neonatal proximal tubules ( P < 0.01). Chloride permeability was 10.94 ± 5.21 × 10−5 cm/s in adult proximal tubules and −1.26 ± 1.84 × 10−5 cm/s in neonatal proximal tubules ( P< 0.05). Thus neonatal PST have a chloride permeability not different from zero and have no net passive chloride transport. Bicarbonate permeability is also less in neonates than adults in this segment (−0.07 ± 0.03 × 10−5 vs. 0.93 ± 0.27 × 10−5 cm/s, P < 0.01). Neonatal PST have higher sodium-to chloride and bicarbonate-to-chloride permeability ratios than adult PST. However, mannitol and sucrose permeabilities were not different in adult proximal tubules and neonatal PST. Transepithelial resistance was measured using current injection and cable analysis. The resistance was 6.7 ± 0.7 Ω · cm2 in adult tubules and 11.3 ± 1.4 Ω · cm2 in neonatal PST ( P < 0.01). In conclusion, there are significant maturational changes in the characteristics of the PST paracellular pathway affecting transport in this nephron segment.

scholarly journals Maturation of rat proximal tubule chloride permeability

2005 ◽  
Vol 289 (6) ◽  
pp. R1659-R1664 ◽  
Author(s):  
Michel Baum ◽  
Raymond Quigley
Keyword(s):  
Chloride Transport ◽  
Proximal Convoluted Tubule ◽  
Proximal Tubules ◽  
Chloride Permeability ◽  
Postnatal Maturation ◽  
Straight Tubule ◽  
Maturational Change ◽  
Proximal Straight Tubule ◽  
Lower Chloride

We have previously shown that neonate rabbit tubules have a lower chloride permeability but comparable mannitol permeability compared with adult proximal tubules. The surprising finding of lower chloride permeability in neonate proximals compared with adults impacts net chloride transport in this segment, which reabsorbs 60% of the filtered chloride in adults. However, this maturational difference in chloride permeability may not be applicable to other species. The present in vitro microperfusion study directly examined the chloride and mannitol permeability using in vitro perfused rat proximal tubules during postnatal maturation. Whereas there was no maturational change in mannitol permeability, chloride permeability was 6.3 ± 1.3 × 10−5 cm/s in neonate rat proximal convoluted tubule and 16.1 ± 2.3 × 10−5 cm/s in adult rat proximal convoluted tubule ( P < 0.01). There was also a maturational increase in chloride permeability in the rat proximal straight tubule (5.1 ± 0.6 × 10−5 cm/s vs. 9.3 ± 0.6 × 10−5 cm/s, P < 0.01). There was no maturational change in bicarbonate-to-chloride permeabilities ( PHCO3/ PCl) in the rat proximal straight tubules (PST) and proximal convoluted tubules (PCT) or in the sodium-to-chloride permeability ( PNa/ PCl) in the proximal straight tubule; however, there was a significant maturational decrease in proximal convoluted tubule PNa/ PCl with postnatal development (1.31 ± 0.12 in neonates vs. 0.75 ± 0.06 in adults, P < 0.001). There was no difference in the transepithelial resistance measured by current injection and cable analysis in the PCT, but there was a maturational decrease in the PST (7.2 ± 0.8 vs. 4.6 ± 0.1 Ω·cm2, P < 0.05). These studies demonstrate there are maturational changes in the rat paracellular pathway that impact net NaCl transport during development.

Effect of luminal chloride on cell pH in rabbit proximal tubule

1988 ◽  
Vol 254 (5) ◽  
pp. F677-F683 ◽  
Author(s):  
M. Baum
Keyword(s):  
Proximal Tubule ◽  
Intracellular Ph ◽  
Apical Membrane ◽  
Chloride Transport ◽  
Disulfonic Acid ◽  
Bathing Solution ◽  
Ph Change ◽  
Base Exchange ◽  
Proximal Tubular

The present in vitro microperfusion study examined whether apical membrane chloride transport is mediated by chloride-base exchange in the rabbit proximal convoluted (PCT) and proximal straight tubule (PST) by examining the effect of the addition of luminal chloride on intracellular pH. Intracellular pH was measured fluorometrically using the pH-sensitive dye 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. In PCT initially perfused without chloride, changing the luminal perfusate to a high chloride (148 mM)-low bicarbonate (5 mM) solution simulating late proximal tubular fluid produced a cell acidification (7.56 +/- 0.06 to 7.52 +/- 0.06, P less than 0.02) when 1 mM formate was present in the perfusate and bathing solution. This acidification was inhibited by 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. This chloride-base exchange was not observed in the absence of formate, and neither acetate nor lactate produced the cell acidification observed with formate. Because the Na+-H+ antiporter could blunt a pH change, 2 mM amiloride was added to the luminal perfusate. While addition of luminal chloride produced a small cell acidification in the absence of formate (7.63 +/- 0.06 to 7.60 +/- 0.05, P less than 0.05), a much greater cell acidification was observed in the presence of 1 mM formate (7.69 +/- 0.05 to 7.58 +/- 0.06, P less than 0.01). Chloride-base exchange was only detected in the presence of formate in the PST. These studies demonstrate apical membrane chloride-base exchange in the presence of formate in the rabbit proximal tubule consistent with chloride-formate exchange.

In vivo proximal tubular fluid-to-plasma chloride concentration gradient in the rabbit

1982 ◽  
Vol 242 (6) ◽  
pp. F575-F579
Author(s):  
R. C. Vari ◽  
C. E. Ott
Keyword(s):  
Proximal Tubule ◽  
Concentration Gradient ◽  
Concentration Ratio ◽  
Mammalian Species ◽  
Chloride Concentration ◽  
Proximal Tubules ◽  
Plasma Chloride ◽  
Tubule Fluid

It has been reported that the concentration of chloride in the proximal tubule is greater than that in plasma in several mammalian species. Much of the theory concerning fluid and electrolyte reabsorption in the proximal tubule is based on data taken from in vitro isolated proximal tubules of the rabbit nephron. This study measured in vivo the rabbit proximal tubule fluid-to-ultrafiltrate chloride concentration ratio [(TF/UF)Cl] and its relationship to proximal tubule length as estimated by the tubule fluid-to-plasma inulin concentration ratio [(TF/P)In]. From six rabbits, 19 random proximal tubules were micropunctured and analyzed for inulin and chloride concentrations, the latter being measured by microelectrometric titration. Plasma ultrafiltrate was determined by correcting plasma chloride concentration for protein concentration. The average single nephron filtration rate was 20.2 +/- 0.8 nl/min. The (TF/UF)Cl ratio was 1.10 +/- 0.03, which was significantly different from unity. Furthermore, regression analysis yielded no significant correlation between the (TF/UF(Cl and (TF/P)In ratio. This study demonstrates that a tubule lumen-to-plasma chloride concentration gradient exists in the in vivo proximal tubule of the rabbit that is apparently established early and is not correlated with proximal tubule length.

Erythrocytes alter the pattern of renal hypoxic injury: predominance of proximal tubular injury with moderate hypoxia

1989 ◽  
Vol 76 (1) ◽  
pp. 19-29 ◽  
Author(s):  
Zoltan H. Endre ◽  
Peter J. Ratcliffe ◽  
John D. Tange ◽  
David J. P. Ferguson ◽  
George K. Radda ◽  
...  
Keyword(s):  
Oxygen Delivery ◽  
Rat Kidney ◽  
Proximal Tubules ◽  
Thick Ascending Limb ◽  
Tubular Injury ◽  
Total Oxygen ◽  
Hypoxic Injury ◽  
Nephron Segment ◽  
Proximal Tubular

1. The distribution of morphological injury was assessed qualitatively and quantitatively in the perfused rat kidney in vitro at controlled rates of oxygen delivery in the presence of low concentrations of erythrocytes. 2. In control kidneys (total oxygen delivery approximately 32 μmol/min per kidney) no injury was seen in the medullary thick ascending limb of Henle's loop (MTAL) whilst 11 ± 5 (sd)% of proximal tubules sustained damage. 3. Mild hypoxia (total oxygen delivery approximately 28 μmol/min per kidney) produced little or no injury to MTAL, namely 6 ± 4(sd)% and 3 ± 3% of tubules damaged, respectively. In contrast, both groups sustained extensive damage to proximal tubules, averaging 46 ± 13% (P < 0.01 vs control) and 84 ± 14% (P < 0.001 vs control), respectively. This damage was equally distributed between the superficial and deep cortex. 4. Comparison with morphometric data obtained previously from cell-free-perfused rat kidneys [P. J. Ratcliffe, Z. H. Endre, S. J. Scheinman, J. D. Tange, J. G. G. Ledingham & G. K. Radda (1988) Clinical Science74, 437–448] showed that (a) erythrocytes prevent hypoxic damage to the MTAL at mild and moderate levels of hypoxia; (b) when oxygen delivery rates are matched between cell-free- and erythrocyte-perfused kidneys, proximal tubular injury is greater in the presence of erythrocytes; (c) when arterial partial pressure of oxygen is matched between cell-free- and erythrocyte-perfused kidneys, the degree of proximal tubular injury is similar. 5. The data suggest that the proximal tubule and not the MTAL is the nephron segment most at risk of hypoxic injury in vitro.

scholarly journals Review: Evidence for a functional intracellular angiotensin system in the proximal tubule of the kidney

2012 ◽  
Vol 302 (5) ◽  
pp. R494-R509 ◽  
Author(s):  
Brianne Ellis ◽  
Xiao C. Li ◽  
Elisa Miguel-Qin ◽  
Victor Gu ◽  
Jia L. Zhuo
Keyword(s):  
Blood Pressure ◽  
Proximal Tubule ◽  
Renin Angiotensin System ◽  
Proximal Tubules ◽  
Renal Physiology ◽  
The Novel ◽  
Ang Ii ◽  
Angiotensin System ◽  
Proximal Tubular

ANG II is the most potent and important member of the classical renin-angiotensin system (RAS). ANG II, once considered to be an endocrine hormone, is now increasingly recognized to also play novel and important paracrine (cell-to-cell) and intracrine (intracellular) roles in cardiovascular and renal physiology and blood pressure regulation. Although an intracrine role of ANG II remains an issue of continuous debates and requires further confirmation, a great deal of research has recently been devoted to uncover the novel actions and elucidate underlying signaling mechanisms of the so-called intracellular ANG II in cardiovascular, neural, and renal systems. The purpose of this article is to provide a comprehensive review of the intracellular actions of ANG II, either administered directly into the cells or expressed as an intracellularly functional fusion protein, and its effects throughout a variety of target tissues susceptible to the impacts of an overactive ANG II, with a particular focus on the proximal tubules of the kidney. While continuously reaffirming the roles of extracellular or circulating ANG II in the proximal tubules, our review will focus on recent evidence obtained for the novel biological roles of intracellular ANG II in cultured proximal tubule cells in vitro and the potential physiological roles of intracellular ANG II in the regulation of proximal tubular reabsorption and blood pressure in rats and mice. It is our hope that the new knowledge on the roles of intracellular ANG II in proximal tubules will serve as a catalyst to stimulate further studies and debates in the field and to help us better understand how extracellular and intracellular ANG II acts independently or interacts with each other, to regulate proximal tubular transport and blood pressure in both physiological and diseased states.

scholarly journals Metabolic substrates alter attachment and differentiated functions of proximal tubule cell culture.

1994 ◽  
Vol 4 (11) ◽  
pp. 1908-1911
Author(s):  
M J Tang ◽  
R L Tannen
Keyword(s):  
Proximal Tubule ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Culture Media ◽  
Proximal Tubules ◽  
Proximal Tubule Cell ◽  
Metabolic Substrates ◽  
Standard Culture ◽  
Leucine Amino Peptidase ◽  
Proximal Tubular

Proximal tubules cultured in vitro gradually lose their differentiated functions. Because standard culture media lacks several substrates important for renal proximal tubule oxidative metabolism, whether a mixture of substrates including butyrate, alanine, and lactate (BAL) would modify growth and/or differentiated function of proximal tubular cells in culture was examined. Tubules cultured in media supplemented with 2 mM butyrate, alanine, and lactate exhibited enhanced attachment but did not exhibit an altered growth rate. Higher levels of phosphoenolpyruvate carboxykinase and leucine-amino peptidase were sustained, although these activities were still diminished in comparison with that in fresh tubules. Sodium-dependent glucose uptake and dome formation--other reflections of epithelial cell differentiated function--also were enhanced. These studies demonstrate that the substrates used to culture proximal tubules can modify both their attachment and their manifestation of differentiated function in culture.

Proximal tubule dysfunction in cystine-loaded tubules: effect of phosphate and metabolic substrates

1996 ◽  
Vol 271 (3) ◽  
pp. F717-F722
Author(s):  
G. Bajaj ◽  
M. Baum
Keyword(s):  
Oxygen Consumption ◽  
Proximal Tubule ◽  
Tricarboxylic Acid Cycle ◽  
Dimethyl Ester ◽  
Proximal Tubules ◽  
Intracellular Atp ◽  
Metabolic Substrates ◽  
Rate Of Oxygen Consumption ◽  
Intracellular Phosphate

Intracellular cystine loading by use of cystine dimethyl ester (CDME) results in a generalized inhibition in proximal tubule transport due, in part, to a decrease in intracellular ATP. The present study examined the importance of phosphate and metabolic substrates in the proximal tubule dysfunction produced by cystine loading. Proximal tubule intracellular phosphorus was 1.8 +/- 0.1 in control tubules and 1.1 +/- 0.1 nmol/mg protein in proximal tubules incubated in vitro with CDME P < 0.001). Infusion of sodium phosphate in rabbits and subsequent incubation of proximal tubules with a high-phosphate medium attenuated the decrease in proximal tubule respiration and prevented the decrease in intracellular ATP with cystine loading. Tricarboxylic acid cycle intermediates have been shown to preserve oxidative metabolism in phosphate-depleted proximal tubules. In proximal tubules incubated with either 1 mM valerate or butyrate, there was a 42 and 34% reduction (both P < 0.05) in the rate of oxygen consumption with cystine loading. However, tubules incubated with 1 mM succinate or citrate had only a 13 and 14% P = NS) reduction in the rate of oxygen consumption, respectively. These data are consistent with a limitation of intracellular phosphate in the pathogenesis of the proximal tubule dysfunction with cystine loading.

Identification of an apical \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{Cl}^{-}{/}\mathrm{HCO}_{3}^{-}\) \end{document} exchanger in rat kidney proximal tubule

2003 ◽  
Vol 285 (3) ◽  
pp. C608-C617 ◽  
Author(s):  
Snezana Petrovic ◽  
Liyun Ma ◽  
Zhaohui Wang ◽  
Manoocher Soleimani
Keyword(s):  
Proximal Tubule ◽  
Apical Membrane ◽  
Rat Kidney ◽  
Proximal Tubules ◽  
Immunocytochemical Staining ◽  
Kidney Cortex ◽  
Rat Kidney Cortex ◽  
Kidney Proximal Tubule ◽  
Anion Transporter

SLC26A6 (or putative anion transporter 1, PAT1) is located on the apical membrane of mouse kidney proximal tubule and mediates [Formula: see text] exchange in in vitro expression systems. We hypothesized that PAT1 along with a [Formula: see text] exchange is present in apical membranes of rat kidney proximal tubules. Northern hybridizations indicated the exclusive expression of SLC26A6 (PAT1 or CFEX) in rat kidney cortex, and immunocytochemical staining localized SLC26A6 on the apical membrane of proximal tubules, with complete prevention of the labeling with the preadsorbed serum. To examine the functional presence of apical [Formula: see text] exchanger, proximal tubules were isolated, microperfused, loaded with the pH-sensitive dye BCPCF-AM, and examined by digital ratiometric imaging. The pH of the perfusate and bath was kept at 7.4. Buffering capacity was measured, and transport rates were calculated as equivalent base flux. The results showed that in the presence of basolateral DIDS (to inhibit [Formula: see text] cotransporter 1) and apical EIPA (to inhibit Na+/H+ exchanger 3), the magnitude of cell acidification in response to addition of luminal Cl– was ∼5.0-fold higher in the presence than in the absence of [Formula: see text]. The Cl–-dependent base transport was inhibited by ∼61% in the presence of 0.5 mM luminal DIDS. The presence of physiological concentrations of oxalate in the lumen (200 μM) did not affect the [Formula: see text] exchange activity. These results are consistent with the presence of SLC26A6 (PAT1) and [Formula: see text] exchanger activity in the apical membrane of rat kidney proximal tubule. We propose that SLC26A6 is likely responsible for the apical [Formula: see text] (and Cl–/OH–) exchanger activities in kidney proximal tubule.

Immunolocalization of NHE8 in rat kidney

2005 ◽  
Vol 288 (3) ◽  
pp. F530-F538 ◽  
Author(s):  
Sunita Goyal ◽  
SueAnn Mentone ◽  
Peter S. Aronson
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Rat Kidney ◽  
Surface Membrane ◽  
Proximal Tubules ◽  
Intense Staining ◽  
Proximal Tubule Cells ◽  
Nephron Segment ◽  
Tubule Cells

In situ hybridization studies demonstrated that Na+/H+ exchanger NHE8 is expressed in kidney proximal tubules. Although membrane fractionation studies suggested apical brush-border localization, precise membrane localization could not be definitively established. The goal of the present study was to develop isoform-specific NHE8 antibodies as a tool to directly establish the localization of NHE8 protein in the kidney by immunocytochemistry. Toward this goal, two sets of antibodies that label different NHE8 epitopes were developed. Monoclonal antibody 7A11 and polyclonal antibody Rab65 both specifically labeled NHE8 by Western blotting as well as by immunofluorescence microscopy. The immunolocalization pattern in the kidney seen with both antibodies was the same, thereby validating NHE8 specificity. In particular, NHE8 expression was observed on the apical brush-border membrane of all proximal tubules from S1 to S3. The most intense staining was evident in proximal tubules in the deeper cortex and medulla with a significant but somewhat weaker staining in superficial proximal tubules. Colocalization studies with γ-glutamyltranspeptidase and megalin indicated expression of NHE8 on both the microvillar surface membrane and the coated-pit region of proximal tubule cells, suggesting that NHE8 may be subject to endocytic retrieval and recycling. Although colocalizing in the proximal tubule with NHE3, no significant alteration in NHE8 protein expression was evident in NHE3-null mice. We conclude that NHE8 is expressed on the apical brush-border membrane of proximal tubule cells, where it may play a role in mediating or regulating ion transport in this nephron segment.

Calcium transport across the pars recta of cortical segment 2 proximal tubules

1986 ◽  
Vol 251 (4) ◽  
pp. F718-F724
Author(s):  
J. E. Bourdeau
Keyword(s):  
Proximal Tubule ◽  
Driving Forces ◽  
Proximal Tubules ◽  
Ion Diffusion ◽  
Low Concentrations ◽  
Pars Recta ◽  
Transepithelial Voltage ◽  
Lower Temperature ◽  
Tubule Fluid

Partes rectae of cortical segment 2 proximal tubules were dissected from rabbit kidneys and perfused in vitro. Ca concentrations of perfused and collected fluids were measured by continuous-flow microcolorimetry. Epithelial Ca permeability (P) was estimated from the bath-to-lumen movement of 45Ca. The transepithelial voltage (psi) and [Ca2+] difference were varied simultaneously by changing perfusate composition. Tubules that were perfused and bathed with an identical artificial ultrafiltrate of plasma displayed a lumen-negative psi, a collectate [Ca] greater than perfusate, and net Ca secretion. Tubules perfused with "late" proximal tubule fluid (high [Cl], low [HCO3], low concentrations of Na+-cotransported solutes) demonstrated a lumen-positive psi, a perfusate [Ca2+] greater than the bath, a collectate [Ca] less than perfusate, and net Ca absorption. Under each of these conditions, net Ca flux was in the direction predicted by the experimentally measured driving forces for diffusional Ca transport. Tubules that were cooled while being perfused with late proximal tubule fluid showed an increased lumen-positive psi but reduced net Ca absorption. The latter finding was consistent with reduced Ca ion diffusion related to a smaller P at the lower temperature. I conclude that Ca2+ diffusion is an important component of net Ca absorption in this segment of the nephron.

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