Electrogenic sodium/bicarbonate cotransport in rabbit renal cortical basolateral membrane vesicles.

Akiba, Takashi; Alpern, Robert J.; Eveloff, Jill; Calamina, J; Warnock, David G.

doi:10.1172/jci112738

Cited by 80 publications

(47 citation statements)

References 33 publications

(28 reference statements)

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“…The results of these studies indicated that vesicles had a predominant right-side orientation with < 15% of them having inside-out orientation. These results are similar to those of other investigators (16).…”

Section: Methodssupporting

confidence: 93%

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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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Section: Methodssupporting

confidence: 93%

“…Basolateral membrane vesicles were prepared from rabbit renal cortex by a modification of differential and percoll gradient centrifugation (15,16). The vesicles were suspended in a medium consisting of 250 mM sucrose, 10 mM Hepes titrated to pH 7.5 with tetramethylammonium (TMA) hydroxide, and then frozen and stored at -70°C until used.…”

Section: Methodsmentioning

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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“…In addition, these studies do not support the presence of a significant apical membrane chloride conductance in vivo. As these cells possess a rheogenic potential difference-sensitive bicarbonate transport mechanism (18,(31)(32)(33)(34)(35)(36), changes in cell potential difference would have been expected to cause changes in cell pH.…”

Section: Discussionmentioning

confidence: 99%

“…The presence of Cl/base exchange in the absence of formate suggests that some Cl/OH,HCO3 exchange is present. As peritubular SITS inhibits the cell's bicarbonate conductance (18,(31)(32)(33)(34)(35)(36) (Fig. 3), and those with acetate (Fig.…”

Section: Discussionmentioning

confidence: 99%

Apical membrane chloride/base exchange in the rat proximal convoluted tubule.

Alpern¹

1987

J. Clin. Invest.

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To examine whether Cl/base exchange is present on the apical membrane of the proximal convoluted tubule, cell pH was measured fluorometrically in the in vivo microperfused rat proximal tubule with (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein.The effect of luminal chloride addition was examined in tubules perfused symmetrically with chloride-free solutions. In the absence of inhibitors, luminal chloride addition did not affect cell pH. However, after inhibition of basolateral membrane anion transport with peritubular 4-acetamido-4'-isothiocyano-(2,2')-disulfonic-stilbene (to amplify effects of apical membrane transport on cell pH), luminal chloride addition caused a small cell acidification (delta pH, = 0.02). When 1 mM formate was added to the solutions, luminal chloride addition caused a larger change in cell pH (delta pH, = 0.06) that was inhibited by (4,4')-diisothiocyano-(2,2')-disulfonic-stilbene. This stimulation of Cl/base exchange was not seen with 1 mM acetate addition. These results demonstrate apical membrane Cl/base exchange, a significant fraction of which is dependent on the presence of formate and probably represents Cl/formate exchange.

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“…In the renal proximal tubule, there is an intimate relation between the apical membrane Na ϩ /H ϩ exchanger and the basolateral membrane sodium bicarbonate co-transporter (NBC). These two transporters are regulated in parallel in response to a variety of experimental maneuvers, hormones, and second messengers (5)(6)(7)(8)(9). The coordinated regulation of NHE3 and NBC appears to be the result of specific regulatory mechanisms and not merely the consequence of the availability of ion substrates for the transporters.…”

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confidence: 99%

Essential Role for NHERF in cAMP-mediated Inhibition of the Na+-HCO3-Co-transporter in BSC-1 Cells

Weinman

Evangelista²,

Steplock³

et al. 2001

Journal of Biological Chemistry

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Prior studies have indicated a requirement for the PDZ domain-containing protein, Na Inhibition of the renal apical membrane Na ϩ /H ϩ exchanger 3 (NHE3) 1 by cAMP-dependent protein kinase (PKA) requires the presence of an additional protein co-factor called the Na ϩ /H ϩ Exchanger Regulatory Factor (NHERF) (1). NHERF contains two tandem PSD-95/Dlg/ZO-1 (PDZ) domains and functions in a signal-complex of proteins, including ezrin, PKA, and NHE3 (1-3). This multiprotein complex facilitates the phosphorylation of NHE3 and the acute down-regulation of its activity (1-3). Subsequent to the elucidation of the role of NHERF in the regulation of NHE3, a role for this protein in the regulation of the activity of other transporters has been proposed, and it has been suggested that the signal-complex model of regulation of renal transport proteins may be more common than currently appreciated (4). In the renal proximal tubule, there is an intimate relation between the apical membrane Na ϩ /H ϩ exchanger and the basolateral membrane sodium bicarbonate co-transporter (NBC). These two transporters are regulated in parallel in response to a variety of experimental maneuvers, hormones, and second messengers (5-9). The coordinated regulation of NHE3 and NBC appears to be the result of specific regulatory mechanisms and not merely the consequence of the availability of ion substrates for the transporters. NBC, like NHE3, is regulated by stimuli that raise intracellular cAMP (8, 9). In association with Bernardo et al. (10), we have previously provided evidence that PKA-mediated inhibition of renal NBC requires NHERF. It is not known, however, if NHERF functions to form a signal-complex that regulates NBC activity or if NBC itself is phosphorylated by PKA. To study the relation between NBC and NHERF, wild-type, truncated, and mutated forms of NHERF were expressed in BSC-1 cells to determine if NHERF binds NBC, if NHERF is required for the phosphorylation of NBC, if the phosphorylation of NHERF is required for NBC regulation, and if NBC requires tethering to the actin cytoskeleton to be regulated by cAMP. The results indicate that the interaction between NHERF and NBC differs from the interactions between NHERF and NHE3. Although the ezrin-radixin-moesin (ERM) binding domain of NHERF is required for cAMP regulation of NBC, NHERF does not bind to NBC or facilitate cAMP-mediated phosphorylation of NBC. Moreover, 15-min treatment of the cells with cAMP does not affect the cell surface expression NBC. It is suggested that cAMP-mediated inhibition of NBC is the result of a biochemical modification of the NBC transporter by a process that requires NHERF but is not associated with phosphorylation of the transporter itself. EXPERIMENTAL PROCEDURESConstruction and Use of NHERF Expression Plasmids-Studies were performed using BSC-1 cells that express endogenous NBC activity but

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Electrogenic sodium/bicarbonate cotransport in rabbit renal cortical basolateral membrane vesicles.

Cited by 80 publications

References 33 publications

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

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

Apical membrane chloride/base exchange in the rat proximal convoluted tubule.

Essential Role for NHERF in cAMP-mediated Inhibition of the Na+-HCO3-Co-transporter in BSC-1 Cells

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