Evidence that parallel Na+-H+ and Cl(-)-HCO3-(OH-) antiporters transport NaCl in the proximal tubule

1987 ◽  
Vol 252 (2) ◽  
pp. F338-F345 ◽  
Author(s):  
M. Baum
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Driving Forces ◽  
Disulfonic Acid ◽  
Albumin Solution ◽  
Nacl Transport ◽  
Volume Absorption ◽  
Proximal Tubular ◽  
High Chloride

The present in vitro microperfusion study examined whether active NaCl transport in the proximal convoluted tubule (PCT) occurs via parallel Na+-H+ and Cl(-)-HCO3-(OH-) exchangers. PCT were perfused with a high-chloride, low-bicarbonate solution simulating late proximal tubular fluid, and were bathed in a similar solution containing 6 g/dl albumin. In this setting the driving forces responsible for passive NaCl transport are eliminated. Addition of 0.1 or 0.5 mM luminal 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), 0.5 mM luminal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), or 0.1 mM bath ethoxyzolamide, a lipophilic carbonic anhydrase inhibitor, resulted in an approximately 50% reduction in volume absorption. Inhibition of the Na+-H+ antiporter with 1.0 mM luminal amiloride inhibited volume absorption by 50%. The transepithelial potential difference (PD) was not significantly different from zero, consistent with an electroneutral mechanism for active NaCl transport. The effect of a Cl(-)-HCO3-(OH-) exchanger on acidification was examined in PCT perfused with an ultrafiltrate-like solution and bathed in a serumlike albumin solution. Addition of 0.5 mM DIDS did not significantly decrease volume absorption, demonstrating that luminal DIDS did not result in a nonspecific decrease in solute transport. Luminal DIDS significantly stimulated bicarbonate absorption, consistent with a Na+-H+ antiporter running in parallel with a Cl(-)-HCO3-(OH-) antiporter, which exchanges luminal Cl- for cellular HCO3- (or OH-). In conclusion, these data are consistent with parallel Na+-H+ and Cl(-)-HCO3-(OH-) antiporters mediating neutral active NaCl transport in the PCT.

scholarly journals Maturation of rabbit proximal straight tubule chloride/base exchange

1998 ◽  
Vol 274 (5) ◽  
pp. F883-F888 ◽  
Author(s):  
Mehul Shah ◽  
Raymond Quigley ◽  
Michel Baum
Keyword(s):  
Adult Rabbit ◽  
Albumin Solution ◽  
Nacl Transport ◽  
Base Exchange ◽  
Straight Tubule ◽  
Volume Absorption ◽  
Straight Tubules ◽  
Proximal Straight Tubule ◽  
Proximal Tubular

The present in vitro microperfusion study compared the mechanism and rates of NaCl transport in neonatal and adult rabbit proximal straight tubules. In proximal straight tubules perfused with a late proximal tubular fluid and bathed in a serumlike albumin solution, the rate of volume absorption ( J V) was 0.54 ± 0.10 and 0.12 ± 0.05 nl ⋅ mm−1 ⋅ min−1in adults and neonates, respectively ( P < 0.05). With the addition of 10−5 M bath ouabain, J Vdecreased to 0.27 ± 0.07 and −0.03 ± 0.04 nl ⋅ mm−1 ⋅ min−1in adult and neonatal tubules, respectively ( P < 0.05), consistent with lower rates of active and passive NaCl transport in the neonatal proximal straight tubule. The effect of luminal sodium and chloride removal on intracellular pH was used to assess the relative rates of Na+/H+and Cl−/base exchange. The rates of Na+/H+and Cl−/base exchange were approximately fivefold less in neonatal proximal straight tubules than adult tubules. In both neonatal and adult proximal straight tubules, the rate of Cl−/base exchange was not affected by formate, bicarbonate, or cyanide and acetazolamide, consistent with Cl−/OH−exchange. These data demonstrate an increase in proximal straight tubule NaCl transport during postnatal renal development.

Heterogeneity of chloride/base exchange in rabbit superficial and juxtamedullary proximal convoluted tubules

1995 ◽  
Vol 268 (5) ◽  
pp. F847-F853 ◽  
Author(s):  
J. N. Sheu ◽  
R. Quigley ◽  
M. Baum
Keyword(s):  
Intracellular Ph ◽  
Rate Of Change ◽  
Disulfonic Acid ◽  
Nacl Transport ◽  
Base Exchange ◽  
Volume Absorption ◽  
Proximal Tubular ◽  
Presence And Absence ◽  
Convoluted Tubules

Active transcellular NaCl transport in the proximal convoluted tubule (PCT) is via apical parallel Na/H and Cl/base exchange. The mechanism of Cl/base exchange remains unclear. The present in vitro microperfusion study examined the mechanism of Cl/base exchange in superficial and juxtamedullary PCT by examining the rate of change in intracellular pH in response to luminal Cl removal. In superficial PCT the rate of Cl/base exchange was 24.0 +/- 2.3 without formate, 36.4 +/- 6.6 with 10 microM formate (P < 0.05), and 43.6 +/- 2.8 pmol.mm-1.min-1 (P < 0.001) with 1 mM luminal formate. Cl/base exchange was inhibited by luminal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) in the presence and absence of formate. In juxtamedullary PCT, Cl/base exchange was 22.2 +/- 3.8 without formate and 25.0 +/- 5.4 pmol.mm-1.min-1 in the presence of 1 mM luminal formate [P = not significant (NS)]. Cl/base exchange was inhibited by luminal DIDS in juxtamedullary PCT. The rates of Cl/base exchange in both superficial and juxtamedullary PCT were not affected by 0.1 mM acetazolamide and 2 mM cyanide and were the same in the presence and absence of HCO3/CO2, consistent with Cl/OH rather than Cl/HCO3 exchange. To examine the effect of formate on PCT transport, tubules were perfused with a high-Cl solution without organics simulating late proximal tubular fluid. In superficial PCT net volume absorption (JV) was 0.00 +/- 0.05 in the absence of formate and 0.14 +/- 0.06 nl.mm-1.min-1 in the presence of 1 mM formate (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Evidence for electroneutral sodium chloride transport in rat proximal convoluted tubule

1986 ◽  
Vol 250 (4) ◽  
pp. F644-F648
Author(s):  
K. J. Howlin ◽  
R. J. Alpern ◽  
C. A. Berry ◽  
F. C. Rector
Keyword(s):  
Sodium Chloride ◽  
Active Transport ◽  
Sodium Transport ◽  
Chloride Transport ◽  
Proximal Convoluted Tubule ◽  
Organic Solutes ◽  
Nacl Transport ◽  
Proximal Tubular ◽  
High Chloride

One- to two-thirds of NaCl absorption in the late proximal convoluted tubule (no luminal organic solutes present) is inhibited by cyanide and thus is dependent on active transport. To examine whether this active transport-dependent NaCl transport is electrogenic or electroneutral, the effect of cyanide on transepithelial potential difference (PD) was measured in the rat proximal convoluted tubule microperfused in vivo. In the presence of an ultrafiltrate-like luminal perfusate containing glucose and alanine, cyanide addition caused the transepithelial PD to change from -0.44 +/- 0.04 to -0.05 +/- 0.03 mV (P less than 0.001). In the presence of a late proximal tubular fluid (high chloride, low bicarbonate, no organics), the transepithelial PD was 1.23 +/- 0.06 mV and was unchanged at 1.19 +/- 0.05 mV after cyanide addition (NS). To eliminate the possibility that an effect of cyanide on a putative acidification-dependent lumen-positive PD was concealing an effect on an electrogenic sodium transport-dependent lumen-negative PD, the above studies were repeated in the presence of acetazolamide. Cyanide did not affect the transepithelial PD (1.17 +/- 0.05 vs. 1.07 +/- 0.06 mV, NS). We conclude that, although cyanide-inhibitable NaCl transport is electrogenic in the presence of luminal organic solutes, it does not generate a transepithelial PD in their absence and therefore is electroneutral.

Effect of carbonic anhydrase inhibition on proximal tubular bicarbonate reabsorption

1963 ◽  
Vol 205 (4) ◽  
pp. 693-696 ◽  
Author(s):  
James R. Clapp ◽  
John F. Watson ◽  
Robert W. Berliner
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Intravenous Administration ◽  
Distal Portion ◽  
Bicarbonate Concentration ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
Carbonic Anhydrase Inhibition ◽  
Before And After ◽  
Proximal Tubular

Samples of fluid from the proximal tubule were collected for the measurement of pH and bicarbonate concentration before and after the administration of acetazolamide (Diamox). Samples collected before acetazolamide were consistently more acid than plasma with the most acid samples coming from the more distal portion of the proximal tubule. After the intravenous administration of acetazolamide, the pH and bicarbonate concentration were consistently higher than in plasma. Bicarbonate concentrations as high as 2.8 times that in plasma were observed. The rise in proximal tubular fluid bicarbonate concentration after acetazolamide is presumably due to a reduction in the rate of bicarbonate reabsorption out of proportion to any impairment in proximal tubular fluid volume reduction.

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.

Mechanism of bicarbonate exit across basolateral membrane of rabbit proximal straight tubule

1987 ◽  
Vol 252 (1) ◽  
pp. F11-F18 ◽  
Author(s):  
S. Sasaki ◽  
T. Shiigai ◽  
N. Yoshiyama ◽  
J. Takeuchi
Keyword(s):  
Negative Charge ◽  
Driving Forces ◽  
Basolateral Membrane ◽  
Disulfonic Acid ◽  
Exit Mechanism ◽  
Total Replacement ◽  
Straight Tubules ◽  
Proximal Straight Tubule ◽  
Basolateral Membrane Potential

To clarify the mechanism(s) of HCO3- (or related base) transport across the basolateral membrane, rabbit proximal straight tubules were perfused in vitro, and intracellular pH (pHi) and Na+ activity (aiNa) were measured by double-barreled ion-selective microelectrodes. Lowering bath HCO3- from 25 to 5 mM at constant PCO2 depolarized basolateral membrane potential (Vbl), and reduced pHi. Most of these changes were inhibited by adding 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) to the bath. Total replacement of bath Na+ with choline also depolarized Vbl and reduced pHi, and these changes were also inhibited by SITS. Reduction in aiNa was observed when bath HCO3- was lowered. Taken together, these findings suggest that HCO3- exists the basolateral membrane with Na+ and negative charge. Calculation of the electrochemical driving forces suggests that the stoichiometry of HCO3-/Na+ must be larger than two for maintaining HCO3- efflux. Total replacement of bath Cl- with isethionate depolarized Vbl gradually and increased pHi slightly, implying the existence of a Cl(-)-related HCO3- exit mechanism. The rate of decrease in pHi induced by lowering bath HCO3- was slightly reduced (20%) by the absence of bath Cl-. Therefore, the importance of Cl(-)-related HCO3- transport is small relative to total basolateral HCO3- exit. Accordingly, these data suggest that most of HCO3- exits the basolateral membrane through the rheogenic Na+/HCO3- cotransport mechanism with a stoichiometry of HCO3-/Na+ of more than two.

scholarly journals Prenatal programming of rat proximal tubule Na+/H+ exchanger by dexamethasone

2007 ◽  
Vol 292 (3) ◽  
pp. R1230-R1235 ◽  
Author(s):  
Amit Dagan ◽  
Jyothsna Gattineni ◽  
Vodi Cook ◽  
Michel Baum
Keyword(s):  
Proximal Tubule ◽  
Membrane Vesicles ◽  
Sodium Reabsorption ◽  
Prenatal Programming ◽  
Sprague Dawley ◽  
Sprague Dawley Rats ◽  
Proximal Tubular ◽  
Old Rats ◽  
Convoluted Tubules

Prenatal administration of dexamethasone causes hypertension in rats when they are studied as adults. Although an increase in tubular sodium reabsorption has been postulated to be a factor programming hypertension, this has never been directly demonstrated. The purpose of this study was to examine whether prenatal programming by dexamethasone affected postnatal proximal tubular transport. Pregnant Sprague-Dawley rats were injected with intraperitoneal dexamethasone (0.2 mg/kg) daily for 4 days between the 15th and 18th days of gestation. Prenatal dexamethasone resulted in an elevation in systolic blood pressure when the rats were studied at 7–8 wk of age compared with vehicle-treated controls: 131 ± 3 vs. 115 ± 3 mmHg ( P < 0.001). The rate of proximal convoluted tubule volume absorption, measured using in vitro microperfusion, was 0.61 + 0.07 nl·mm−1·min−1 in control rats and 0.93+ 0.07 nl·mm−1·min−1 in rats that received prenatal dexamethasone ( P < 0.05). Na+/H+ exchanger activity measured in perfused tubules in vitro using the pH-sensitive dye BCECF showed a similar 50% increase in activity in proximal convoluted tubules from rats treated with prenatal dexamethasone. Although there was no change in abundance of NHE3 mRNA, the predominant luminal proximal tubule Na+/H+ exchanger, there was an increase in NHE3 protein abundance on brush-border membrane vesicles in 7- to 8-wk-old rats receiving prenatal dexamethasone. In conclusion, prenatal administration of dexamethasone in rats increases proximal tubule transport when rats are studied at 7–8 wk old, in part by stimulating Na+/H+ exchanger activity. The increase in proximal tubule transport may be a factor mediating the hypertension by prenatal programming with dexamethasone.

Transepithelial acidification by cultures of rabbit proximal tubules grown on filters

1990 ◽  
Vol 259 (1) ◽  
pp. C103-C109 ◽  
Author(s):  
S. M. Ford ◽  
P. D. Williams ◽  
S. Grassl ◽  
P. D. Holohan
Keyword(s):  
Proximal Tubule ◽  
Cultured Cells ◽  
Ph Gradient ◽  
Transport Systems ◽  
Disulfonic Acid ◽  
Intact Cells ◽  
Proximal Tubule Cells ◽  
Membrane Filters ◽  
Apical Chamber

Transepithelial acidification in the proximal tubule occurs by the simultaneous actions of the Na(+)-H+ exchanger in the brush border and the basolateral Na(+)-HCO3- cotransporter. The presence of these systems has been demonstrated for cultured cells; however, their contributions to the transepithelial movement of acid equivalents has not been confirmed in monolayers. To examine transepithelial acidification by intact cells, tubules were grown on membrane filters. Confluent cultures developed a transepithelial pH gradient within 6 h by decreasing the pH of medium in the apical chamber (6.66 +/- 0.03) while raising the basolateral pH to 7.40 +/- 0.02. Cells maintained on plastic did not acidify the medium during this time. Amiloride (10-100 microM) inhibited development of the gradient only when placed in the top chamber. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS; 10-100 microM), which inhibits basolateral Na(+)-HCO3- cotransport, decreased the gradient only when added to the bottom. These results demonstrate that cultured proximal tubule cells can develop a transepithelial pH gradient and that the polarized distribution of the transport systems is maintained in vitro.

Acidification mechanisms on the basolateral membrane of renal vesicles from the developing nephron

1990 ◽  
Vol 259 (3) ◽  
pp. F458-F465
Author(s):  
M. Baum
Keyword(s):  
Proximal Tubule ◽  
Voltage Clamp ◽  
Basolateral Membrane ◽  
Disulfonic Acid ◽  
Co2 Removal ◽  
Loop Of Henle ◽  
Base Exchange ◽  
Newborn Rabbit ◽  
Renal Vesicle

The present study examined acidification mechanisms on the basolateral membrane of the early renal vesicle, an undifferentiated ball of cells that will develop into parts of the glomerulus, proximal tubule, loop of Henle, and a portion of the distal convoluted tubule. Renal vesicles were dissected from newborn rabbit kidneys and bathed in vitro. To examine the basolateral membrane acidification mechanisms, intracellular pH (pHi) was measured by use of the pH-sensitive dye (2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Evidence for Cl(-)-base exchange included the fact that removal of bath Cl-resulted in cell alkalinization (7.35 +/- 0.03 to 7.48 +/- 0.05; P less than 0.01). Cell alkalinization induced by Cl- removal was also observed in presence of a voltage clamp without bath Na+ (7.18 +/- 0.02 to 7.39 +/- 0.04; P less than 0.01) and was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). pHi recovery after acute alkalinization resulting from CO2 removal was 0.20 +/- 0.03 pH units/min in the presence of Cl-, 0.07 +/- 0.01 in experiments with 0.2 mM DIDS, and 0.07 +/- 0.01 in absence of bath Cl-. The early renal vesicle also has a basolateral Na(+)-H+ antiporter. Removal of bath Na+ resulted in cell acidification (7.36 +/- 0.09 to 7.18 +/- 0.06; P less than 0.01), which was inhibited by 2 mM amiloride. Cell pH recovery after acute acidification (NH4Cl prepulse technique) was entirely dependent on bath Na+ and inhibited by amiloride. Thus the renal vesicle has basolateral membrane Na(+)-H+ and Cl(-)-base exchangers that can defend against cell acidification and alkalinization, respectively.

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