The SLC26 gene family encodes anion transporters with diverse functional attributes: (a) anion exchanger, (b) anion sensor and (c) anion conductance (likely channel). We have cloned and studied Slc26a9, a paralog expressed mostly in lung and stomach. Immunohistochemistry shows that Slc26a9 is present at apical and intracellular membranes of lung and stomach epithelia. Using expression in Xenopus laevis oocytes and ion-sensitive microelectrodes, we discovered that Slc26a9 has a novel function not found in any other Slc26 proteins -cation coupling. Intracellular pH and voltage measurements show that Slc26a9 is a nCl --HCO 3 -exchanger, suggesting roles in gastric HCl secretion or pulmonary HCO 3 -secretion; Na + electrodes and uptakes reveal that Slc26a9 has a cationdependence. Single channel measurements indicate that Slc26a9 displays discrete open and close states. These experiments show that Slc26a9 has three discrete physiological modes: nCl --HCO 3 -exchanger, Cl -channel, and Na + -anion cotransporter. Thus, the Slc26a9 transporter-channel is uniquely suited for dynamic and tissue-specific physiology or regulation in epithelial tissues.

We have shown that the renal sulfate transport system has dual roles in euryhaline eel, namely, maintenance of sulfate homeostasis and osmoregulation of body fluids. To clarify the physiological roles of sulfate transporters in teleost fish, we cloned orthologs of the mammalian renal sulfate transporters Slc13a1 (NaSi-1) and Slc26a1 (Sat-1) from eel (Anguilla japonica) and assessed their functional characteristics, tissue localization, and regulated expression. Full-length cDNAs coding for ajSlc13a1 and ajSlc26a1 were isolated from a freshwater eel kidney cDNA library. Functional expression in Xenopus oocytes revealed the expected sulfate transport characteristics; furthermore, both transporters were inhibited by mercuric chloride. Northern blot analysis, in situ hybridization, and immunohistochemistry demonstrated robust apical and basolateral expression of ajSlc13a1 and ajSlc26a1, respectively, within the proximal tubule of freshwater eel kidney. Expression was dramatically reduced after the transfer of eels from freshwater to seawater; the circulating sulfate concentration in eels was in turn markedly elevated in freshwater compared with seawater conditions (19 mM vs. 1 mM). The reabsorption of sulfate via the apical ajSlc13a1 and basolateral ajSlc26a1 transporters may thus contribute to freshwater osmoregulation in euryhaline eels, via the regulation of circulating sulfate concentration. freshwater adaptation; immunohistochemistry; sulfate transporter; renal proximal tubule SULFATE IS ESSENTIAL for a variety of metabolic and cellular processes, including production of highly sulfated proteoglycans by chondrocytes, detoxification, and elimination of xenobiotics and endogenous compounds by sulfoconjugation in the liver and kidney, and biosynthesis of sulfated hormones such as gastrin and cholecystokinin (27). Mechanisms regulating the levels of plasma sulfate are therefore essential for the maintenance of normal physiology. In mammals, the regulation of sulfate homeostasis is largely determined by the kidney, with the major fraction of filtered sulfate being reabsorbed in the proximal tubule. Two sulfate transporters have been identified that are involved in this reabsorption of sulfate from the glomerular ultrafiltrate: solute carrier family 13a1 (Slc13a1; NaSi-1) and solute carrier family 26a1 (Slc26a1; Sat-1). Slc13a1 is an electrogenic Na ϩ -dependent sulfate transporter (alternatively called Na ϩ -SO 4 2Ϫ cotransporter) that is located in the apical membrane of renal proximal tubule cells and mediates entry of Na ϩ -SO 4 2Ϫ with a stoichiometry of 3:1 (5, 24). Slc26a1 is sulfate/anion exchanger mediating SO 4 2Ϫ efflux across the basolateral membrane in exchange for HCO 3 Ϫ (17). Physiological significance of this regulatory system is well established in mammals through targeted disruption of the Slc13a1 gene (9).Physiological studies on sulfate homeostasis also have been conducted in nonmammalian systems, including those of birds (12,40,44,45), bivalve (11), and fish (10, 36, 37, 43, 46 -49). However, li...

The neuron-specific K ؉ -Cl ؊ cotransporter KCC2 plays a crucial role in determining intracellular chloride activity and thus the neuronal response to ␥-aminobutyric acid and glycine.

Abstract. SLC26 anion exchangers transport monovalent and divalent anions, with a diversity of anion specifi city and stoichiometry. Our