Mediates electroneutral potassium-chloride cotransport when activated by cell swelling. May contribute to cell volume homeostasis in single cells. May be involved in the regulation of basolateral Cl(-) exit in NaCl absorbing epithelia (By similarity). Isoform 4 has no transport activity. Inhibited by WNK3. Homomultimer and heteromultimer with other K-Cl cotransporters. Experimental confirmation may be lacking for some isoforms. Ubiquitous. Levels are much higher in erythrocytes from patients with Hb SC and Hb SS compared to normal AA erythrocytes. This may contribute to red blood cell dehydration and to the manifestation of sickle cell disease by increasing the intracellular concentration of HbS. Isoform 1 was not detected in circulating reticulocytes. N-glycosylated. Belongs to the SLC12A transporter family. Truncated N-terminus.