What is the effect of aldosterone on Na+ and K+ handling in the distal nephron?

• A. Increases Na+ reabsorption and stimulates K+ secretion.
• B. Decreases Na+ reabsorption and decreases K+ secretion.
• C. Decreases Na+ reabsorption and stimulates K+ reabsorption.
• D. Increases Na+ excretion and stimulates K+ secretion.

Answer: (A)

Aldosterone increases Na+ reabsorption in the distal nephron and stimulates K+ secretion.

Aldosterone acts on principal cells in the late distal tubule and collecting duct by binding mineralocorticoid receptors, which boosts the production of ENaC channels on the apical membrane and Na+/K+ ATPase on the basolateral side. More Na+ is reabsorbed from the tubular lumen into the blood. As Na+ is reabsorbed, the lumen becomes more negatively charged, driving K+ to be secreted into the lumen via apical K+ channels, increasing its excretion. So the net effect is more Na+ reabsorption and more K+ secretion, matching the correct choice.