Renal and intestinal transport defects in Slc26a6-null mice

Wang

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

et al. 2005

Self Cite

Na-H exchanger NHE3 and Cl-anion exchanger CFEX (SLC26A6, PAT1) play principal roles in the reabsorption of Na and Cl in the proximal tubule of the mammalian kidney. The mechanisms by which NHE3 and CFEX are localized to and maintained in the brush border of the proximal tubule are largely unknown. To investigate the possible interaction of NHE3 and CFEX with the PDZ-domaincontaining scaffolding protein PDZK1, we performed a series of in vitro interaction assays with GST-fusion proteins and native brush border membrane proteins. These studies demonstrated that, not only were NHE3 and CFEX capable of directly interacting with PDZK1, but that this interaction was mediated through their C-terminal PDZ-interaction sites. To determine whether PDZK1 interaction is essential for brush border localization of NHE3 and CFEX in vivo, we examined the expression of NHE3 and CFEX in kidneys of wild-type and PDZK1-null mutant mice by both Western analysis and immunocytochemistry. These studies indicated that, although brush border expression of NHE3 was unaffected by the loss of PDZK1, the expression of CFEX was markedly reduced. Finally, we assayed CFEX functional activity as Cl-oxalate exchange in brush border membrane vesicles and oxalate-stimulated volume absorption in microperfused proximal tubules. Consistent with the observed decrease in CFEX protein expression, both measures of CFEX functional activity were dramatically reduced in PDZK1-null animals. In conclusion, the scaffolding protein PDZK1 is essential for the normal expression and function of Cl-anion exchanger CFEX in the proximal tubule of the mammalian kidney.NHE3 ͉ proximal tubule ͉ SLC26A6

Section: Nhe3 ͉ Proximal Tubule ͉ Slc26a6mentioning

confidence: 99%

Section: The Interaction Of Cfex With Pdzk1 Is Also Mediated Through mentioning

confidence: 99%

Role of PDZK1 in membrane expression of renal brush border ion exchangers

Wang

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

et al. 2005

Self Cite

Journal of Experimental Biology

“…However, an important function of HCO 3 -secretion in the duodenum is protection of the duodenal epithelium from the acidic chyme delivered from the stomach into the small intestine (Allen and Flemstrom, 2005 of the eutherian duodenum are SLC26A3 and SLC26A6 (Jacob et al, 2002;Singh et al, 2008;Tuo et al, 2006;Walker et al, 2009). However, SLC26A6 contributes little to HCO 3 -secretion (Wang et al, 2005) whereas SLC26A3 is responsible for ~60% of the spontaneous HCO 3 -secretion and ~50% of the cAMP-stimulated secretion, CFTR and a small paracellular leak accounting for the remainder (Walker et al, 2009). It is generally accepted that SLC26A6 is electrogenic (Jiang et al, 2002;Ko et al, 2002;Xie et al, 2002) with an apparent stoichiometry of 1Cl -:2HCO 3 - (Shcheynikov et al, 2006), and early evidence suggested that SLC26A3 was also electrogenic, but with a stoichiometry of 2Cl -:1HCO 3 -, opposite that of SLC26A6 (Ko et al, 2002;Shcheynikov et al, 2006).…”

Section: Discussionmentioning

confidence: 99%

The distribution and expression of CFTR restricts electrogenic anion secretion to the ileum of the brushtail possum, Trichosurus vulpecula

Gill

Bartolo

Demmers

et al. 2011

SUMMARYIn eutherian mammals, fluid secretion is essential for intestinal function. This is driven by electrogenic Cl -secretion, which involves a NaK2Cl cotransporter (NKCC1) in the enterocyte basolateral membrane and the cystic fibrosis transmembrane conductance regulator (CFTR) in the apical membrane. However, in the possum ileum, NKCC1 expression is low and secretagogues stimulate electrogenic HCO 3 -secretion driven by a basolateral NaHCO 3 cotransporter (pNBCe1). Here we investigated whether electrogenic anion secretion occurs in possum duodenum and jejunum and determined the role of CFTR in possum intestinal anion secretion. Prostaglandin E 2 (PGE 2 ) and forskolin stimulated a large increase in ileal short-circuit current (I sc ), consistent with electrogenic HCO 3 -secretion, but had little effect on the duodenal and jejunal I sc . Furthermore, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and N-(2-naphthalenyl)-[(3,5-dibromo-2,4-dihydroxyphenyl)methylene]glycine hydrazide (GlyH101) inhibited cloned possum CFTR in cultured cells and the PGE 2 -stimulated ileal I sc , implicating CFTR in ileal HCO 3 -secretion. Consistent with this, CFTR is expressed in the apical membrane of ileal crypt and lower villous cells, which also express pNBCe1 in the basolateral membrane. In contrast, duodenal and jejunal CFTR expression is low relative to the ileum. Jejunal pNBCe1 expression is also low, whereas duodenal and ileal pNBCe1 expression are comparable. All regions have low NKCC1 expression. These results indicate that cAMP-dependent electrogenic Cl -secretion does not occur in the possum small intestine because of the absence of CFTR and NKCC1. Furthermore, CFTR functions as the apical anion conductance associated with HCO 3 -secretion and its distribution limits electrogenic HCO 3 -secretion to the ileum.

American Journal of Physiology-Gastrointestinal and Liver Physi

“…Here, we show that H ϩ can alternatively exit across the apical membrane, facilitating luminal HCO 3 absorption. We have demonstrated that all of the JacobsStewart cycle-associated proteins are well expressed in duodenal epithelial cells (3,40) and that cytosolic and membranebound CA activities are essential for luminal H ϩ uptake (27). We now would like to further test the hypothesis that H ϩ , CO 2 , and HCO 3 Ϫ absorption pathways across the apical membrane of duodenal epithelial cells follow the model of the JacobsStewart cycle.…”

Section: Epithelial Hcomentioning

confidence: 92%

“…The two major apical transporters that secrete HCO 3 Ϫ into the duodenal lumen are the cystic fibrosis transmembrane conductance regulator (CFTR) and the apical Cl Ϫ /HCO 3 Ϫ anion exchanger in the SLC26A family (9,40). CFTR plays a major role in the HCO 3 Ϫ secretion stimulated by the cAMP pathway (9).…”

Section: Epithelial Hcomentioning

confidence: 99%

CFTR inhibition augments NHE3 activity during luminal high CO₂exposure in rat duodenal mucosa

Mizumori

Choi²,

Guth³

et al. 2008

We hypothesized that the function of duodenocyte apical membrane acid-base transporters are essential for H ϩ absorption from the lumen. We thus examined the effect of inhibition of Na ϩ /H ϩ exchanger-3 (NHE3), cystic fibrosis transmembrane regulator (CFTR), or apical anion exchangers on transmucosal CO 2 diffusion and HCO 3 Ϫ secretion in rat duodenum. Duodena were perfused with a pH 6.4 high CO 2 solution or pH 2.2 low CO2 solution with the NHE3 inhibitor, S3226, the anion transport inhibitor, DIDS, or pretreatment with the potent CFTR inhibitor, CFTRinh-172, with simultaneous measurements of luminal and portal venous (PV) pH and carbon dioxide concentration ([CO2] Ϫ loss by NHE3 inhibition and reduced intracellular acidification during CFTR inhibition is consistent with activation or unmasking of NHE3 activity by CFTR inhibition, increasing cell surface H ϩ available to neutralize luminal HCO 3 Ϫ with consequent CO2 absorption. NHE3, by secreting H ϩ into the luminal microclimate, facilitates net transmucosal HCO 3 Ϫ absorption with a mechanism similar to proximal tubular HCO 3 Ϫ absorption.CO 2 absorption; bicarbonate secretion; portal venous PCO2 EPITHELIAL HCO 3 Ϫ SECRETION is considered to be the primary defense against duodenal injury from gastric acid. One of the unexplained mysteries of duodenal HCO 3 Ϫ secretion is why it is needed, given that secretion into the lumen from pancreas and liver is more than adequate to fully neutralize the bulk luminal content (13). Epithelial HCO 3 Ϫ secretion has thus been hypothesized to neutralize a distinct "preepithelial layer" adjacent to the apical plasma membrane of the mucosa (10, 24). Moreover, the upper intestine absorbs HCO 3 Ϫ by an electroneutral Na ϩ -dependent mechanism, hypothesized to be Na ϩ /H ϩ exchange (37). Since the epithelial Na ϩ /H ϩ exchanger (NHE) 3, which helps facilitate intestinal neutral NaCl absorption, is highly expressed in duodenum (31), we wondered whether duodenal NHE3 additionally functions as an H ϩ secretor, as it does in the proximal tubule (33, 38), facilitating HCO 3 Ϫ absorption. The duodenum must also absorb ϳ450 mmol of gastric H ϩ /24 h to decrease luminal hydrogen concentration ([H ϩ ]) by 6 log orders over its 15-cm length (12). HCl in the duodenal lumen is neutralized by HCO 3 Ϫ secreted by the pancreas and duodenal epithelium. This generates extremely high luminal CO 2 pressures (PCO 2 Ͼ 400 Torr), which are dissipated by the proximal jejunum (32). Gastric mucosal CO 2 and H ϩ permeability is low, since pyloric obstruction leads to severe metabolic alkalosis due to the inability of the normal stomach to absorb substantial quantities of H ϩ or CO 2 (16). Thus the duodenum is the major site for intestinal H ϩ and CO 2 absorption.We have demonstrated sequential transmucosal CO 2 and H ϩ movement from duodenal lumen into the portal vein (PV), facilitated by epithelial cytosolic and membrane-bound carbonic anhydrases (CAs) in the rat (27). Cellular acidification by luminal CO 2 /H ϩ rapidly induces protective responses su...