Regulation of cell pH by ambient bicarbonate, carbon dioxide tension, and pH in the rabbit proximal convoluted tubule.

Krapf, Reto; Berry, Christine; Alpern, Robert J.; Rector, Floyd C.

doi:10.1172/jci113330

Cited by 36 publications

(34 citation statements)

References 40 publications

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“…For the analysis of the luminal Na/H antiporter by luminal sodium removal, the solutions were HCO3-free, containing Hepes and 0. i mM acetazolamide in luminal and bath perfusates (solutions 3 and 4, Table I). Previous studies have shown that analysis of luminal transporters is facilitated by effectively blocking the rate of the basolateral transporters, because these latter transporters are more important determinants of cell pH (8,15). We have also demonstrated that the Na/(HCO3)3 cotransporter is fully inhibited in the absence of exogenous C02/HCO3 and 0.1 mM acetazolamide and that acetazolamide does not affect the rate of the Na/H antiporter in this setting (12).…”

Section: Resultsmentioning

confidence: 99%

“…On the basolateral side, bicarbonate can be transported via a Na/(HCO3)3 cotransporter or via chloride-coupled transporters. The overwhelming majority of bicarbonate reabsorption and cell pH regulation in the proximal tubule is dependent on sodium (2-8) while chloride removal does not affect the rates of bicarbonate reabsorption and the regulation of cell pH by acute changes in ambient Pco2 (4,7,8). Thus, the luminal Na/H antiporter and the basolateral Na/(HCO3)3 cotransporter are probably the two most important transporters involved in both transcellular bicarbonate transport and the cell pH response to changes in ambient Pco2.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms of adaptation to chronic respiratory acidosis in the rabbit proximal tubule

Krapf

1989

Journal of Critical Care

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The hyperbicarbonatemia of chronic respiratory acidosis is maintained by enhanced bicarbonate reabsorption in the proximal tubule. To investigate the cellular mechanisms involved in this adaptation, cell and luminal pH were measured microfluorometrically using (2M,7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein in isolated, microperfused S2 proximal convoluted tubules from control and acidotic rabbits. Chronic respiratory acidosis was induced by exposure to 10% CO2 for 52-56 h. Tubules from acidotic rabbits had a significantly lower luminal pH after 1-mm perfused length (7.03±0.09 vs. 7.26±0.06 in controls, perfusion rate = 10 nl/min). Chronic respiratory acidosis increased the initial rate of cell acidification (dpH1/dt) in response to luminal sodium removal by 63% and in response to lowering luminal pH (7.4-6.8) by 69%. Chronic respiratory acidosis also increased dpH,/dt in response to peritubular sodium removal by 63% and in response to lowering peritubular pH by 73%. In conclusion, chronic respiratory acidosis induces a parallel increase in the rates of the luminal Na/H antiporter and the basolateral Na/(HCO3)3 cotransporter. Therefore, the enhanced proximal tubule reabsorption of bicarbonate in chronic respiratory acidosis may be, at least in part, mediated by a parallel adaptation of these transporters.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanisms of adaptation to chronic respiratory acidosis in the rabbit proximal tubule

Krapf

1989

Journal of Critical Care

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“…Na/H antiporter activity was assayed as the Na-dependent increase in pH, after an acid load. This assay was performed in the absence of C02/HCO3 to eliminate any contribution from the Na(HCO3)2/Cl exchanger or the Na/3HCO3 cotransporter (26,27). The observation that amiloride inhibited most of the Na-dependent pHi recovery in proximal tubule cells and in fibroblasts confirms that this goal was achieved.…”

Section: Discussionmentioning

confidence: 98%

Preincubation in acid medium increases Na/H antiporter activity in cultured renal proximal tubule cells.

Horie

Moe

Tejedor

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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Chronic acidosis in vivo leads to an increase in proximal tubule Na/H antiporter activity that persists when the transporter is studied out of the acidotic environment. It is presently not clear whether a decrease in extracellular fluid pH alone is sufficient to elicit this adaptation. The present studies examined the effect of acid preincubation on Na/H antiporter activity in cultured proximal tubule cells. Antiporter activity was examined after a 2-day preincubation in control or acid medium, 1 hr after removal from the preincubation fluid.Na/H antiporter activity was assayed as the initial rate of (vol/vol) to the culture medium for the first 3 days to allow better cell attachment. After achieving confluence (8-12 days), cells were rendered quiescent by removal of insulin and hydrocortisone for 48 hr prior to and during preincubation (10).Cultured fibroblasts were derived from human foreskin and used in passages 5-7 (11). Fibroblasts were grown on glass coverslips in DMEM supplemented with penicillin (100 units/ ml), streptomycin (100 ,ug/ml), and 10% fetal bovine serum. Fibroblasts were incubated with a reduced concentration of fetal bovine serum (1%) for 24 hr prior to and during preincubation.Measurement of Intracellular pH and Na/H Antiporter Activity. Continuous measurement of cytoplasmic pH (pHi) was accomplished using the intracellularly trapped pHsensitive dye 2',7'-bis(2-carboxyethyl)-5-(and -6)carboxyfluorescein (BCECF acid). Cells were loaded with the acetoxymethyl ester of BCECF (10 ,uM)

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“…Comparison between cell pH response at acidic and alkaline pH is complicated by the fact that at acidic cell pH (induced by low luminal pH), the basolateral Na+:CO7 :HCO-cotransporter is reversed and works as an "alkaline loader." This is also the case when both luminal and peritubular pH and HCO-are increased (22).…”

Section: Resultsmentioning

confidence: 81%

“…Using the pH-sensitive dye BCECF, Krapf et al evaluated the role ofthe luminal Na+/H+ exchanger and basolateral Nae:CO7 :HCO-cotransporter in cell pH regulation in the intact perfused tubule (22). Increasing luminal pH increased and decreasing luminal pH decreased cell pH.…”

Section: Resultsmentioning

confidence: 99%

A pH modifier site regulates activity of the Na+:HCO3- cotransporter in basolateral membranes of kidney proximal tubules.

Soleimani

Lesoine²,

Bergman³

et al. 1991

J. Clin. Invest.

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HCO3 exit across the basolateral membrane of the kidney proximal tubule cell is mediated via an electrogenic Na+: cotransporter. In these experiments, we have studied the effect of internal pH on the activity of the Na+:HCO-cotransport system in basolateral membrane vesicles isolated from rabbit renal cortex. Equilibrium thermodynamics predicts that in the presence of constant intravesicular concentration of Na+, an increasing concentration of HCO3 will be associated with an increasing driving force for Na+:HCO3 cotransport across the vesicles. Our experimental approach was to preequilibrate the membrane vesicles with 1 mM 22Na' at pH1 6.8-8.0 and known concentrations of HCO3. The vesicles were diluted 1:100 into Na+-free solution at pH 7.4 and the net flux of 22Na+ was assayed over 5 s. The results demonstrate that the net flux of Na+ was significantly higher at pH1 7.2 than pH, 8.0 despite much higher IHCO3I at pHi 8.0. This suggests that an internal pHsensitive site regulates the activity of the Na+:HCO-cotransporter. This modifier site inhibits the cotransporter at alkaline pH despite significant base concentration and is maximally functional around physiologic pH. The combination of modifier sites on the luminal Na+/H+ exchanger and the basolateral Na+:HCO-cotransporter should help maintain intracellular pH in a narrow range with changes in extracellular pH. (J.

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Regulation of cell pH by ambient bicarbonate, carbon dioxide tension, and pH in the rabbit proximal convoluted tubule.

Abstract: To study the regulation of cell pH by ambient pH, carbon dioxide tension (Pco2), and bicarbonate (HCO3), cell pH was measured in the isolated, in vitro microperfused rabbit proximal convoluted tubule using the fluorescent dye (2',7')-bis-(carboxyethyl)- (5,6)

Cited by 36 publications

References 40 publications

Mechanisms of adaptation to chronic respiratory acidosis in the rabbit proximal tubule

Mechanisms of adaptation to chronic respiratory acidosis in the rabbit proximal tubule

Preincubation in acid medium increases Na/H antiporter activity in cultured renal proximal tubule cells.

A pH modifier site regulates activity of the Na+:HCO3- cotransporter in basolateral membranes of kidney proximal tubules.

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