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)

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.

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.

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.

Axial heterogeneity of rabbit proximal tubule luminal H+ and basolateral HCO3- transport

1989 ◽  
Vol 256 (2) ◽  
pp. F335-F341
Author(s):  
M. Baum
Keyword(s):  
Proximal Tubule ◽  
Intracellular Ph ◽  
Basolateral Membrane ◽  
Sodium Concentration ◽  
Rate Of Change ◽  
Bathing Solution ◽  
Proton Secretion ◽  
Sodium Dependent ◽  
Convoluted Tubules

The present in vitro microperfusion study examined whether the rates of the apical membrane Na+-H+ antiporter and basolateral membrane Na(HCO3)3 symporter vary along the length of the proximal tubule. Initial proximal convoluted tubules (PCT obtained within 0.5 mm from the glomerulus), mid-PCT (PCT without glomerular attachments) and cortical proximal straight tubules were examined. The rate of either the apical or basolateral membrane acidification mechanism was measured from the initial rate of change of intracellular pH after a change in either the luminal or bathing solution. Intracellular pH was measured fluorometrically using the pH-sensitive dye (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein. The rate of bicarbonate exit across the basolateral membrane was examined by imposing either a sodium or bicarbonate gradient. There was no difference between initial and mid-PCT, but the rate of change in cell pH was 30% slower in PST in both series. The rate of sodium-dependent apical proton secretion was examined by changing the sodium concentration in the lumen. There was no difference in sodium-dependent apical proton secretion in initial vs. mid-PCT, but the rate fell by 70% in the proximal straight tubule (PST). These differences were not due to a difference in buffer capacity in these segments. These data are consistent with a homogeneous rate of apical Na+-H+ antiporter and basolateral Na(HCO3)3 activity along the rabbit PCT, but a lower rate in the PST.

SITS-sensitive basolateral anion current in rabbit proximal convoluted tubules

1988 ◽  
Vol 254 (6) ◽  
pp. F828-F836
Author(s):  
M. Kuwahara ◽  
F. C. Rector ◽  
C. A. Berry
Keyword(s):  
Steady State ◽  
Chloride Transport ◽  
Basolateral Membrane ◽  
Mean Value ◽  
Disulfonic Acid ◽  
Total Chloride ◽  
Proximal Tubular ◽  
Convoluted Tubules ◽  
Proximal Convoluted Tubules

To assess the presence and nature of steady-state anion current across the basolateral membrane in in vitro rabbit proximal convoluted tubules bathed and perfused with a high-chloride, low-bicarbonate solution simulating late proximal tubular fluid, steady-state basolateral cell membrane potential difference (Vb1) was measured by conventional microelectrodes. The mean value of Vb1 was -52 mV. Addition of 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) to the bath solution hyperpolarized Vb1 by 30 mV, suggesting the presence of basolateral anion current. Total chloride removal did not change Vb1 significantly, and formate, a presumptive stimulant of electroneutral sodium chloride transport, depolarized Vb1 both in the presence and absence of chloride, suggesting that the formate-stimulated change in Vb1 was chloride independent. In the total absence of chloride and bicarbonate, 1 mM bath SITS and 0.1 mM lumen and bath acetazolamide hyperpolarized Vb1 by 27–35 and 23 mV, respectively. These results suggest that the SITS-sensitive change in Vb1 is independent of chloride and associated with a basolateral anion current that is predominantly due to bicarbonate exit. In the absence of exogenous CO2, cell-to-bath HCO3-dependent anion current can be derived from metabolic CO2.

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.

Intracellular pH in the OK cell. I. Identification of H+ conductance and observations on buffering capacity

1991 ◽  
Vol 261 (6) ◽  
pp. C1143-C1153 ◽  
Author(s):  
M. Graber ◽  
J. DiPaola ◽  
F. L. Hsiang ◽  
C. Barry ◽  
E. Pastoriza
Keyword(s):  
Steady State ◽  
Intracellular Ph ◽  
Large Cell ◽  
Buffering Capacity ◽  
Disulfonic Acid ◽  
Transport Pathways ◽  
Opossum Kidney ◽  
Direct Titration ◽  
Cell Ph

The regulation of intracellular pH (pHi) in the opossum kidney (OK) cell line was studied in vitro using the pH-sensitive excitation ratio of 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Recovery from an NH4Cl acid load disclosed a Na-dependent component blocked by amiloride and a smaller Na-independent component. The Na-independent recovery rate was proportional to the H+ gradient from cell to buffer and was zero in the absence of an electrochemical gradient. The Na-independent recovery was not affected by N-ethylmaleimide, dicyclohexylcarbodiimide, HCO3, phloretin, or ZnCl2 but was accelerated in depolarized cells and by membrane-fluidizing drugs and was inhibited by glutaraldehyde. The apparent cellular buffering capacity changed in proportion to this H+ conductance. Consistent with an electrogenic H+ leak, steady-state cell pH alkalinized with depolarization and acidified with hyperpolarization. Removal of buffer Na+ produced a profound acidification, as did amiloride. In 0-Na+ buffers, extremely large cell-to-buffer H+ gradients were present and proportional to buffer pH. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid had no effect on steady-state pHi. Measurements of intracellular buffering capacity were derived from the change of cell pH induced by withdrawing NH4Cl. This buffering capacity was increased threefold in Na-free buffers, whereas the value measured by direct titration of cell lysate was the same or less than that of control cells. The NH4Cl-derived buffering capacity varied in direct proportion to the magnitude of the H+ leak. Drugs that changed H+ permeability produced the apparent changes of the measured buffering capacity within a few minutes. We conclude that, in HCO3-free buffer, the OK cell uses two membrane acid-base transport pathways: a Na-H antiporter active at physiological pH and a substantial passive H+ conductance. The results also reveal that the NH4Cl-derived buffering capacity is subject to artifacts, possibly due to a finite leak of ionic NH4+.

Effect of potassium on proximal tubular function

1978 ◽  
Vol 234 (5) ◽  
pp. F381-F385 ◽  
Author(s):  
J. Cardinal ◽  
D. Duchesneau
Keyword(s):  
Renal Tubule ◽  
Potential Difference ◽  
Tubular Function ◽  
Fluid Absorption ◽  
Bathing Medium ◽  
Sodium Potassium ◽  
Proximal Tubular ◽  
Proximal Tubular Function ◽  
Convoluted Tubules

In order to study the effect of potassium on the renal tubule, proximal convoluted tubules were dissected from rabbit kidneys and perfused in vitro. Omitting potassium from both the perfusate and bath caused the rate of fluid absorption and the transtubular potential difference to fall to zero. This effect was due to the absence of potassium in the bathing medium since no change was observed when potassium was omitted from the perfusate only. With 0.5 and 1.0 meq/liter of potassium in the bath, there was still a significant decrease from control in both the potential difference and the rate of fluid absorption. With 2.5 meq/liter of potassium in the bath, the results did not differ from control. In further studies, tubules were perfused with 10 meq/liter of potassium in both perfusate and bath. There was no change in the potential difference of fluid absorption. These results are consistent with the view that active transtubular transport of sodium is linked to the influx of potassium into the cell at the peritubular membrane and that this is probably mediated by sodium-potassium-ATPase. Our results also suggest that the variations of potassium concentration in the physiological range do not affect proximal tubular function.

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.

Potassium conductance regulation by pH during volume regulation in rabbit proximal convoluted tubules

1992 ◽  
Vol 263 (3) ◽  
pp. F453-F458 ◽  
Author(s):  
J. S. Beck ◽  
S. Breton ◽  
G. Giebisch ◽  
R. Laprade
Keyword(s):  
Intracellular Ph ◽  
Basolateral Membrane ◽  
Potassium Conductance ◽  
Membrane Resistance ◽  
Disulfonic Acid ◽  
Bicarbonate Transport ◽  
Hypotonic Shock ◽  
Reduction Of Co2 ◽  
Convoluted Tubules ◽  
Proximal Convoluted Tubules

When rabbit proximal convoluted tubules were microperfused in the presence of bicarbonate, a 90 mosmol hypotonic shock hyperpolarized the basolateral membrane by 5.5 +/- 1.4 mV, increased basolateral potassium selectivity (tK) from 0.30 +/- 0.02 to 0.45 +/- 0.02, and reduced the basolateral membrane resistance from 4,887 +/- 821 to 2,836 +/- 602 omega.cm. These data show that the hypotonic shock increased absolute basolateral potassium conductance. The same hypotonic shock elevated intracellular pH from 7.18 +/- 0.04 to 7.31 +/- 0.04. When bath pH was increased by 0.2 pH units (by reduction of CO2), intracellular pH rose by 0.13 +/- 0.01. In separate experiments this maneuver hyperpolarized the basolateral membrane by 5.0 +/- 0.8 mV and augmented basolateral tK from 0.58 +/- 0.06 to 0.68 +/- 0.04, suggesting that the basolateral potassium conductance is sensitive to pH changes of a magnitude similar to that evoked by a hypotonic shock. In the nominal absence of bicarbonate or presence of 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) in the bath, the hypotonic shock caused a transient intracellular acidification, suggesting involvement of basolateral bicarbonate transport in the hypotonic shock-induced alkalinization. In the absence of bicarbonate, the hypotonic shock did not increase basolateral tK or induce hyperpolarization of the basolateral membrane. We conclude that the increase in potassium conductance observed during hypotonic shock is at least partly mediated by a bicarbonate-dependent, SITS-sensitive intracellular alkalinization.

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