Multifunctional transporter with an impact in cell morphology and differentiation. In the presence of borate B(OH)4(-), acts as a voltage-dependent electrogenic Na(+)-coupled B(OH)4(-) cotransporter controlling boron homeostasis (PubMed:15525507). At early stages of stem cell differentiation, participates in synergy with ITGA5-ITGB1 and ITGAV-ITGB3 integrins and BMPR1A to promote cell adhesion and contractility that drives differentiation toward osteogenic commitment while inhibiting adipogenesis (By similarity). In the absence of B(OH)4(-), acts as a Na(+)-coupled OH(-) or H(+) permeable channel with implications in cellular redox balance (PubMed:15525507, PubMed:28642546). Regulates the oxidative stress response in corneal endothelium by enhancing antioxidant defenses and protecting cells from reactive oxygen species (PubMed:28642546). In response to hypo-osmotic challenge, also acts as water permeable channel at the basolateral cell membrane of corneal endothelial cells and facilitates transendothelial fluid reabsorption in the aqueous humor (PubMed:31273259, PubMed:25007886, PubMed:23813972). In the presence of ammonia, acts as an electrogenic NH3/H(+) cotransporter and may play a role in ammonia transport and reabsorption in renal Henle's loop epithelium (PubMed:27581649). 2 Na(+)(in) + tetrahydroxoborate(in) = 2 Na(+)(out) + tetrahydroxoborate(out) Homodimer. Widely expressed. Highly expressed in kidney, testis, salivary gland, thyroid, trachea and corneal endothelium. Not detected in retina and lymphocytes. Expressed in corneal endothelium (at protein level). The predominant isoform in corneal endothelium (at protein level). Up-regulated upon oxidative stress, as it occurs in cells exposed to tert-butyl hydroperoxide. Glycosylated. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Isoforms 1 and 5 correspond to alternative translation start site of the same transcript. There is no evidence that isoform 1 is expressed in primary tissues. It is shown that it is not expressed in cornea, however it is strongly expressed upon transfection into HEK-293 cells. Belongs to the anion exchanger (TC 2.A.31) family. Extended N-terminus.