Cellular mechanisms of renal potassium transport: cortical collecting tubule. A, Principal cells of the cortical collecting duct: apical sodium channels play a key role in potassium secretion by increasing the intracellular sodium available to Na+-K+-ATPase pumps and by creating a favorable electrical potential for potassium secretion. Basolateral Na+-K+-ATPase creates a favorable concentration gradient for passive diffusion of potassium from cell to lumen through potassium-selective channels. B, Intercalated cells. Under conditions of potassium depletion, the cortical collecting duct becomes a site for net potassium reabsorption. The H+-K+-ATPase pump is regulated by potassium intake. Decreases in total body potassium increase pump activity, resulting in enhanced potassium reabsorption. This pump may be partly responsible for the maintenance of metabolic alkalosis in conditions of potassium depletion [11].

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