Pendrin is an anion transporter encoded by the PDS͞Pds gene. In humans, mutations in PDS cause the genetic disorder Pendred syndrome, which is associated with deafness and goiter. Previous studies have shown that this gene has a relatively restricted pattern of expression, with PDS͞Pds mRNA detected only in the thyroid, inner ear, and kidney. The present study examined the distribution and function of pendrin in the mammalian kidney. Immunolocalization studies were performed using anti-pendrin polyclonal and monoclonal antibodies. Labeling was detected on the apical surface of a subpopulation of cells within the cortical collecting ducts (CCDs) that also express the H ؉ -ATPase but not aquaporin-2, indicating that pendrin is present in intercalated cells of the CCD. Furthermore, pendrin was detected exclusively within the subpopulation of intercalated cells that express the H ؉ -ATPase but not the anion exchanger 1 (AE1) and that are thought to mediate bicarbonate secretion. The same distribution of pendrin was observed in mouse, rat, and human kidney. However, pendrin was not detected in kidneys from a Pds-knockout mouse. Perfused CCD tubules isolated from alkali-loaded wild-type mice secreted bicarbonate, whereas tubules from alkali-loaded Pds-knockout mice failed to secrete bicarbonate. Together, these studies indicate that pendrin is an apical anion transporter in intercalated cells of CCDs and has an essential role in renal bicarbonate secretion.

Abstract-Slc26a4 (Pds, pendrin) is an anion transporter expressed in the apical region of type B and non-A, non-B intercalated cells of the distal nephron. It is upregulated by aldosterone analogues and is critical in the development of mineralocorticoid-induced hypertension. Thus, Slc26a4 expression and its role in blood pressure and fluid and electrolyte homeostasis was explored during NaCl restriction, a treatment model in which aldosterone is appropriately increased. Ultrastructural immunolocalization, balance studies, and cortical collecting ducts (CCDs) perfused in vitro were used. With moderate physiological NaCl restriction, Slc26a4 expression in the apical plasma membrane increased 2-to 3-fold in type B intercalated cells. Because Slc26a4 transports Cl Ϫ , we tested whether NaCl balance differs in Slc26a4 (ϩ/ϩ) (Ϫ/Ϫ) mice had evidence of relative vascular volume depletion because they had a higher arterial pH, hematocrit, and blood urea nitrogen than wild-type mice. With moderate NaCl restriction, blood pressure was similar in Slc26a4 (ϩ/ϩ) and Slc26a4 (Ϫ/Ϫ) mice. However, on a severely restricted intake of NaCl, Slc26a4 (Ϫ/Ϫ) mice were hypotensive relative to wild-type mice. We conclude that Slc26a4 is upregulated with NaCl restriction and is critical in the maintenance of acid-base balance and in the renal conservation of Cl Ϫ and water during NaCl restriction.

Background: Pendred syndrome, a common autosomal-recessive disorder characterized by congenital deafness and goiter, is caused by mutations of SLC26A4, which codes for pendrin. We investigated the relationship between pendrin and deafness using mice that have (Slc26a4 +/+ ) or lack a complete Slc26a4 gene (Slc26a4 -/-).

Prior RNA sequencing (RNA-seq) studies have identified complete transcriptomes for most renal epithelial cell types. The exceptions are the cell types that make up the renal collecting duct, namely intercalated cells (ICs) and principal cells (PCs), which account for only a small fraction of the kidney mass, but play critical physiological roles in the regulation of blood pressure, extracellular fluid volume, and extracellular fluid composition. To enrich these cell types, we used FACS that employed well-established lectin cell surface markers for PCs and type B ICs, as well as a newly identified cell surface marker for type A ICs, c-Kit. Single-cell RNA-seq using the IC- and PC-enriched populations as input enabled identification of complete transcriptomes of A-ICs, B-ICs, and PCs. The data were used to create a freely accessible online gene-expression database for collecting duct cells. This database allowed identification of genes that are selectively expressed in each cell type, including cell-surface receptors, transcription factors, transporters, and secreted proteins. The analysis also identified a small fraction of hybrid cells expressing aquaporin-2 and anion exchanger 1 or pendrin transcripts. In many cases, mRNAs for receptors and their ligands were identified in different cells (e.g., chiefly in PCs vs. chiefly in ICs), suggesting signaling cross-talk among the three cell types. The identified patterns of gene expression among the three types of collecting duct cells provide a foundation for understanding physiological regulation and pathophysiology in the renal collecting duct.

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 amiloridesensitive 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 -/HCO 3 -exchanger (NDCBE/SLC4A8) and the Na + -independent Cl -/HCO 3 -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.

Pendrin is an anion exchanger expressed in type B intercalated cells of the cortical collecting duct (CCD). Whether pendrin localizes to other nephron segments with intercalated cells is unknown. Moreover, whether pendrin is expressed in proximal tubule is debated. Thus the distribution of pendrin mRNA and protein expression in mouse kidney was investigated by using light and electron microscopic immunohistochemistry and quantitative real-time PCR. We observed that pendrin mRNA is expressed mainly in cortex. Within cortex, pendrin mRNA is at least fivefold higher in CCD and the connecting tubule (CNT) than in the other segments. Pendrin protein was observed in a subset of cells within the distal convoluted tubule as well as in type B and in non-A-non-B intercalated cells of the CNT and CCD. In type B intercalated cells, pendrin immunoreactivity was highest in apical cytoplasmic vesicles with little immunolabel along the apical plasma membrane. In non-A-non-B intercalated cells, intense pendrin immunoreactivity was detected along the apical plasma membrane. These differences in the subcellular distribution of pendrin immunolabel were confirmed by morphometric analysis. In conclusion, pendrin is expressed in the mouse distal convoluted tubule, CCD, and CNT along the apical plasma membrane of non-A-non-B intercalated cells and in subapical cytoplasmic vesicles of type B intercalated cells.

Abstract-Pendrin is an anion exchanger expressed along the apical plasma membrane and apical cytoplasmic vesicles of type B and of non-A, non-B intercalated cells of the distal convoluted tubule, connecting tubule, and cortical collecting duct. Thus, Pds (Slc26a4) is a candidate gene for the putative apical anion-exchange process of the type B intercalated cell. Because apical anion exchange-mediated transport is upregulated with deoxycorticosterone pivalate (DOCP), we tested whether Pds mRNA and protein expression in mouse kidney were upregulated after administration of this aldosterone analogue by using quantitative real-time polymerase chain reaction as well as light and electron microscopic immunolocalization. In kidneys from DOCP-treated mice, Pds mRNA increased 60%, whereas pendrin protein expression in the apical plasma membrane increased 2-fold in non-A, non-B intercalated cells and increased 6-fold in type B cells. Because pendrin transports HCO 3 -and Cl -, we tested whether DOCP treatment unmasks abnormalities in acid-base or NaCl balance in Pds (-/-) mice. In the absence of DOCP, arterial pH, systolic blood pressure, and body weight were similar in Pds (ϩ/ϩ) and Pds (-/-) mice. After DOCP treatment, weight gain and hypertension were observed in Pds (ϩ/ϩ) but not in Pds (-/-) mice. Moreover, after DOCP administration, metabolic alkalosis was more severe in Pds (-/-) than Pds (ϩ/ϩ) mice. We conclude that pendrin is upregulated with aldosterone analogues and is critical in the pathogenesis of mineralocorticoid-induced hypertension and metabolic alkalosis.

Pendrin (encoded by Pds, Slc26a4) is a Cl−/HCO3− exchanger expressed in the apical regions of type B and non-A, non-B intercalated cells of kidney and mediates renal Cl− absorption, particularly when upregulated. Aldosterone increases blood pressure by increasing absorption of both Na+ and Cl− through increased protein abundance and function of Na+ transporters, such as the epithelial Na+ channel (ENaC) and the Na+-Cl− cotransporter (NCC), as well as Cl− transporters, such as pendrin. Because aldosterone analogs do not increase blood pressure in Slc26a4−/− mice, we asked whether Na+ excretion and Na+ transporter protein abundance are altered in kidneys from these mutant mice. Thus wild-type and Slc26a4-null mice were given a NaCl-replete, a NaCl-restricted, or NaCl-replete diet and aldosterone or aldosterone analogs. Abundance of the major renal Na+ transporters was examined with immunoblots and immunohistochemistry. Slc26a4-null mice showed an impaired ability to conserve Na+ during dietary NaCl restriction. Under treatment conditions in which circulating aldosterone is increased, α-, β-, and 85-kDa γ-ENaC subunit protein abundances were reduced 15–35%, whereas abundance of the 70-kDa fragment of γ-ENaC was reduced ∼70% in Slc26a4-null relative to wild-type mice. Moreover, ENaC-dependent changes in transepithelial voltage were much lower in cortical collecting ducts from Slc26a4-null than from wild-type mice. Thus, in kidney, ENaC protein abundance and function are modulated by pendrin or through a pendrin-dependent downstream event. The reduced ENaC protein abundance and function observed in Slc26a4-null mice contribute to their lower blood pressure and reduced ability to conserve Na+ during NaCl restriction.