The Na+-dependent chloride-bicarbonate exchanger SLC4A8 mediates an electroneutral Na+ reabsorption process in the renal cortical collecting ducts of mice
Françoise Leviel, … , Régine Chambrey, Dominique Eladari
Françoise Leviel, … , Régine Chambrey, Dominique Eladari
Published April 12, 2010
Citation Information: J Clin Invest. 2010;120(5):1627-1635. https://doi.org/10.1172/JCI40145.
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Research Article

The Na+-dependent chloride-bicarbonate exchanger SLC4A8 mediates an electroneutral Na+ reabsorption process in the renal cortical collecting ducts of mice

Abstract

Regulation of sodium balance is a critical factor in the maintenance of euvolemia, and dysregulation of renal sodium excretion results in disorders of altered intravascular volume, such as hypertension. The amiloride-sensitive epithelial sodium channel (ENaC) is thought to be the only mechanism for sodium transport in the cortical collecting duct (CCD) of the kidney. However, it has been found that much of the sodium absorption in the CCD is actually amiloride insensitive and sensitive to thiazide diuretics, which also block the Na-Cl cotransporter (NCC) located in the distal convoluted tubule. In this study, we have demonstrated the presence of electroneutral, amiloride-resistant, thiazide-sensitive, transepithelial NaCl absorption in mouse CCDs, which persists even with genetic disruption of ENaC. Furthermore, hydrochlorothiazide (HCTZ) increased excretion of Na+ and Cl– in mice devoid of the thiazide target NCC, suggesting that an additional mechanism might account for this effect. Studies on isolated CCDs suggested that the parallel action of the Na+-driven Cl–/HCO3– exchanger (NDCBE/SLC4A8) and the Na+-independent Cl–/HCO3– exchanger (pendrin/SLC26A4) accounted for the electroneutral thiazide-sensitive sodium transport. Furthermore, genetic ablation of SLC4A8 abolished thiazide-sensitive NaCl transport in the CCD. These studies establish what we believe to be a novel role for NDCBE in mediating substantial Na+ reabsorption in the CCD and suggest a role for this transporter in the regulation of fluid homeostasis in mice.

Authors

Françoise Leviel, Christian A. Hübner, Pascal Houillier, Luciana Morla, Soumaya El Moghrabi, Gaëlle Brideau, Hassan Hatim, Mark D. Parker, Ingo Kurth, Alexandra Kougioumtzes, Anne Sinning, Vladimir Pech, Kent A. Riemondy, R. Lance Miller, Edith Hummler, Gary E. Shull, Peter S. Aronson, Alain Doucet, Susan M. Wall, Régine Chambrey, Dominique Eladari

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Figure 7

Effects of HCTZ (10–4 M) on NDCBE or PDS activity in isolated collecting ducts or on recombinant NDCBE or PDS expressed in Xenopus oocytes.

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Effects of HCTZ (10–4 M) on NDCBE or PDS activity in isolated collecting...
(A) Effects of HCTZ and Ndcbe disruption on Na+-dependent pHi changes measured in intercalated cells of CCD isolated from Na-depleted Ndcbe–/– or Ndcbe+/+ mice fed a low-Na+ diet. Traces are the average of pHi changes recorded when luminal Na+ was removed and then readded, in the presence of extracellular Cl– (122 mM) and HCO3– (25 mM). Intracellular Na+-dependent acidification was detected in Ndcbe+/+ mice but absent in Ndcbe–/– mice or when HCTZ 10–4 M was present in the perfusate. In these 3 different experimental conditions, mean starting pHi values were 7.10 ± 0.02, 6.93 ± 0.11, and 7.01 ± 0.04, respectively. (B) Effects of HCTZ on apical Cl–/HCO3– exchange activity in intercalated cells of CCDs isolated from Na-depleted animals. Traces are the average of pHi changes recorded when luminal Cl– was removed and then readded, in the presence of extracellular HCO3– (25 mM) and in Na+-free solutions. Intracellular Cl–-dependent alkalinization, reflecting apical Cl–/HCO3– exchange, was completely abolished when 10–4 M HCTZ was present in the perfusate. Mean starting pHi values (immediately before Cl– removal) were 6.91 ± 0.03 and 6.89 ± 0.08, in the absence and presence of HCTZ, respectively. (C) Effects of HCTZ on mNdcbe-mediated HCO3– influx. Oocytes had been injected with mNdcbe cRNA or H2O and incubated with HCTZ (0.25 mM). As a control, NDCBE-expressing and H2O-injected oocytes were incubated with vehicle (methanol). Values are mean ± SEM with 6–9 oocytes per group. **P < 0.01, ***P < 0.001 versus H2O-injected oocyte. HCO3– flux was unaffected by the application of HCTZ (0.25 mM) compared with vehicle alone (P = 0.279). (D) Effects of HCTZ on Pds-mediated 36Cl– uptake. Pendrin-expressing oocytes (mPds) were incubated in ND96 containing 0.1 or 1 mM HCTZ during the uptake period (16 minutes). As a control, pendrin-expressing and H2O-injected oocytes were incubated with vehicle (methanol). Values are mean ± SEM, with 6–16 oocytes per group. *P < 0.001 versus H2O; †P < 0.001 versus mPds, HCTZ 0.1 mM.