Transporter which plays an important role in sodium-mediated fluid transport in different organs. Prevents severe morphological changes of the cornea caused by increased sodium chloride concentrations in the stroma. In the inner ear, is involved in transport of potassium through the fibrocyte layer to the stria vascularis and is essential for the generation of the endocochlear potential but not for regulation of potassium concentrations in the endolymph. In the kidney, is essential for urinary concentration, mediates a sodium flux into the thin descending limb of Henle loop to allow countercurrent multiplication by osmotic equilibration By similarity. Involved in borate homeostasis. In the absence of borate, it functions as a Na+ and OH-(H+) channel. In the presence of borate functions as an electrogenic Na+ coupled borate cotransporter.Parker M.D., Biochem. Biophys. Res. Commun. 282:1103-1109(2001).Deloukas P., Nature 414:865-871(2001).Ota T., Nat. Genet. 36:40-45(2004).