The [[Na-K-Cl cotransporter]] ([[NKCC]]) is a protein that aids in the secondary active transport of sodium, potassium, and chloride into cells. In humans there are two isoforms of this membrane transport protein, [[NKCC1]] and NKCC2, encoded by two different genes (SLC12A2 and SLC12A1 respectively). Two isoforms of the NKCC1/Slc12a2 gene result from keeping (isoform 1) or skipping (isoform 2) exon 21 in the final gene product.