Mediates electroneutral potassium-chloride cotransport. May be activated by cell swelling. May contribute to cell volume homeostasis in single cells. Inhibited by WNK3. Homomultimer and heteromultimer with other K-Cl cotransporters. Isoform 1 is highly expressed throughout the brain and detected at lower levels in kidney. Highly expressed in highly myelinated white matter of the brain, but not in gray matter. Detected in the corpus callosum, in packed cell layers of the hippocampus and in Purkinje neurons within the cerebellum. Highly expressed in white matter in the spinal cord, but not in dorsal root ganglia or sciatic nerve. Colocalizes with the oligodendrocyte marker CNP. Isoform 2 is highly expressed in kidney, but not detected in brain. N-glycosylated. Defects in Slc12a6 are a cause of locomotor abnormalities beginning at 2 weeks of age. Slc12a6 deficient mice show hypomyelination, decompaction of myelin, demyelination, axonal swelling and fiber degeneration. Produced by alternative promoter usage. Belongs to the SLC12A transporter family.