Physiology of electrogenic SLC26 paralogues

SLC26 anion exchangers transport monovalent and divalent anions, with a diversity of anion specificity and stoichiometry. Our microelectrode studies indicate that several SLC26 members are electrogenic. We reported that Slc26a6 functions as a Cl^-/formate, Cl^-/oxalate, Cl ^-/OH^- and electrogenic Cl^-/nHCO ₃^- exchanger. Recently, we have also confirmed that Slc26a7 does not behave as a Cl^-/HCO₃^- exchanger but does function as an electrogenic anion conductance, perhaps a channel. We have also cloned murine Slc26a9, which is strongly expressed in the respiratory tract and stomach. Radioisotope uptakes in Xenopus oocytes indicate that Slc26a9 is a highly selective anion exchanger, transporting Cl^- but neither formate, oxalate, nor SO₄^2-. We also utilized electrophysiology to voltage clamp (VC) and/or measure intracellular pH (pH _i), Cl^- ([Cl^-]_i) and Na⁺ ([Na⁺]_i), in response to various ion replacements. Cl ^- removal in HCO₃^- depolarizes oocytes (to > +60 mV), alkalinizes oocytes, and decreases aCl_i^-. Slc26a9 thus functions as an electrogenic nCl^-/HCO₃ ^- exchanger, suggesting a role in pulmonary and gastric HCO ₃^- secretion and/or CO₂ transport. VC experiments revealed channel-like currents (>10 μA at -60 mV and >80 μA at +60 mV) mediated by Slc26a9 in the presence and absence of HCO ₃^-. Our experiments and those of others continue to reveal additional characteristics and unique roles for this new class of electrogenic anion transporters.