Functions as a beta-subunit for CLCNKA and CLCNKB chloride channels. In the kidney CLCNK/BSND heteromers mediate chloride reabsorption by facilitating its basolateral efflux. In the stria, CLCNK/BSND channels drive potassium secretion by recycling chloride for the basolateral SLC12A2 cotransporter. Interacts with CLCNK channels. Forms probably heteromers with CLCNKA in the thin ascending limb of Henle and with CLCNKB in the thick ascending limb and more distal segments. Staining in membranes of the renal tubule is basolateral. Also detected in basolateral membranes of intercalated cells of the collecting duct, which are known to express CLCNKB as well. Both acid-secreting alpha-intercalated cells and base-secreting beta-intercalated cells express this protein basolaterally, but intervening AQP2-expressing principal cells appear devoid of protein expression. In the inner ear, colocalizes with CLCNK in K(+)-secreting marginal cells of the stria vascularis. The basolateral staining contrasts with the apical localization of the KCNQ1 K(+) channel. Also found in K(+)-secreting vestibular dark cells, where it colocalized in basolateral membranes with CLCNK below apical membranes that expressed KCNQ1. Expression is evident in inner and outer stripes of the outer medulla of the kidney, most probably representing thin limbs of Henle's loop together with some collecting duct coursing through the outer stripe. In situ hybridization in fetal kidney at 18.5 dpc revealed a clear continuity between hybridization signals from the thin limb of Henle's loop and the distal convoluted tubule, suggesting that part of the expression pattern may result from expression in the thick ascending limb of Henle's loop. In addition, strong signals are present in a subset of cortical tubules, representing distal convoluted tubules or cortical collecting duct. Strong expression is also observed in the inner medulla of the kidney. This expression does not extend all the way to the tip of the papilla. Thus this signal most probably represents cells of the thin ascending limbs. In the inner ear, strong and exclusive expression is detected in marginal cells of the stria vascularis. In addition to cochlear signal, expression is observed in dark cells localized at the base of the crista ampullaris of the vestibular organ. Palmitoylation is necessary for activation of plasma membrane-inserted CLC-K/barttin channels.