The Na+-dependent chloride-bicarbonate exchanger SLC4A8 mediates an electroneutral Na+ reabsorption process in the renal cortical collecting ducts of mice
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
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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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 6

Detection and functional characterization of NDCBE in collecting ducts isolated from wild-type mice fed a Na+-depleted diet.

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Detection and functional characterization of NDCBE in collecting ducts i...
(A) Na+ dependence of pHi changes in intercalated cells of CCDs isolated from mice fed a Na+-depleted diet. Traces are the average of pHi changes recorded when luminal Na+ was removed from, and then readded to the perfusate. Upper-left panel: Both Cl– and HCO3–/CO2 were present in the extracellular fluid; mean starting pHi (immediately before luminal Na+ removal) was 7.03 ± 0.04. Upper right: extracellular Cl– was absent; mean starting pHi was 7.03 ± 0.05. Lower left: extracellular HCO3–/CO2 was absent; mean starting pHi was 7.09 ± 0.11. Lower right: initial rates of pHi changes during exposure to different solutions. Values are mean ± SEM, with number of tubules in parentheses. Statistical significance was tested by ANOVA followed by Bonferroni’s post-hoc test. **P < 0.01 versus all other groups. o, outside. (B) Western blot analyses of NDCBE in the mouse kidney and CCD. Western blot analyses of 50 μg membrane fraction proteins from renal cortex isolated from Ndcbe–/– mice or wild-type mice or of proteins from 100 CCDs (corresponding to ~25 mm of tubule) isolated from wild-type mice. NDCBE was detected in the renal cortex or isolated tubules of wild-type but not of Ndcbe –/– mice. Note that the apparent difference in abundance of NDCBE between the lane loaded with total cortex and the one loaded with isolated CCD does not reflect an enrichment of the cortex versus the CCD, but actually only reflects the difference in the quantity of protein loaded. (C) Analyses of amiloride-resistant Na+ and Cl– transepithelial fluxes in CCDs isolated from NDCBE-KO mice maintained on a Na+-depleted diet. Fluxes were measured in the presence of 10–5 M amiloride in the perfusate to reflect only the amiloride-resistant, HCTZ-sensitive component of NaCl reabsorption. Values are mean ± SEM; statistical significance was assessed by unpaired Student’s t test with Welch’s correction, when appropriate. n = 5 in each group.