Renal sodium, potassium and chloride ion cotransporter that mediates the transepithelial NaCl reabsorption in the thick ascending limb and plays an essential role in the urinary concentration and volume regulation. Electrically silent transporter system. Activated by WNK3. When phosphorylated, interacts with PPP3CB. Predominantly expressed in kidney (at protein level). Kidney-specific; most highly expressed in the inner stripe of outer medulla (at protein level). Kidney-specific; most highly expressed in the outer stripe of outer medulla (at protein level). Kidney-specific; most highly expressed in the cortical thick ascending limb (at protein level). Short-term cyclosporine administration increases SLC12A1 phosphorylation in kidney thick ascending limb, possibly through the inhibition of PPP3CB/calcineurin A beta phosphatase. Belongs to the SLC12A transporter family.