Ion transport in loop of Henle

Schematic representation of the transport mechanisms in the thick ascending limb of the loop of Henle. The Na-K-ATPase pump in the basolateral (peritubular) membrane pumps Na out of, and K into, the cell. This creates a low intracellular Na concentration, which drives the electroneutral Na-K-2Cl cotransporter (NKCC2) at the apical membrane. The inward movement of K and Cl occurs against their electrochemical gradients and is powered by the inward movement of Na into the cell. The Na that enters the cell is pumped out by the Na-K-ATPase. Much of the K that enters the cell across the apical membrane recycles back into the lumen through K channels (ROMK) in the apical membrane, allowing continued NaCl uptake. The Cl that enters the cells leaves through chloride channels in the basolateral membrane, primarily Clc-Kb channels, encoded by CLCNKB. This movement of cationic K into the lumen plus the flux of reabsorbed Cl out of the cell into the peritubular capillary (via chloride channels) causes the lumen to become more positively charged, compared with the peritubular space. This electrical potential drives cation reabsorption, of Na, Ca, and Mg, across the paracellular tight junction, through selective pathways.