NKCC2, a kidney-specific member of the cation chloride co-transporter family SLC12, facilitates transport of sodium, potassium, and chloride ions from the lumen of the renal thick ascending limb into the cell (1, 2). Transport of sodium dilutes the luminal fluid, decreasing its osmolality creating an osmotic driving force for water reabsorption in the connecting tubule and cortical collecting duct under the influence of the hormone vasopressin. NKCC2 is found on the apical surface of the thick ascending limb of the loop of Henle and is blocked by loop diuretics such as furosemide (1).