Figure 2.

This figure shows K⁺ handling by the kidney. Proximal convoluted tubule: 65% K⁺ is reabsorbed. Thick ascending loop of Henle: K⁺ enters the cell via the Na⁺–K⁺–2Cl⁻ cotransporter. Early distal convoluted tubule: Na⁺ and Cl⁻ reabsorbed by Na⁺–Cl⁻ cotransporter. K⁺ is secreted into the lumen via the renal outer medullary potassium channel. Late distal convoluted tubule, connecting tubule, and cortical collecting duct: (1) Principal cells: K⁺ secreted into the lumen by the renal outer medullary potassium channels and K⁺ maxi conductance channels. Epithelial Na channel shifts Na from the lumen to inside the cell. (2) Intercalated cells Type A: K⁺ taken up inside the cell from the lumen with the help of K⁺–H⁺ exchanger