In vitro activity: Triamterene inhibits the epithelial sodium channels on principal cells in the late distal convoluted tubule and collecting tubule, which are responsible for 1-2% of total sodium reabsorption. Triamterene can achieve a modest amount of diuresis by decreasing the osmotic gradient necessary for water reabsorption from lumen to interstitium. Triamterene also has a potassium-sparing effect. Normally, the process of potassium excretion is driven by the electrochemical gradient produced by sodium reabsorption. As sodium is reabsorbed, it leaves a negative potential in the lumen, while producing a positive potential in the principal cell. This potential promotes potassium excretion through apical potassium channels. By inhibiting sodium reabsorption, triamterene also inhibits potassium excretion.

Mol Pharmacol. 2003 Oct;64(4):848-56; Int J Clin Pharmacol Ther. 2005 Jul;43(7):327-34.