Diuretics, specific agents amiloride

Both agents appear to affect Na+ reabsorption in the cortical collecting duct. A site in the connecting tubule also may be involved. Although amiloride has been more extensively studied than triamterene, both diuretics specifically block the apical membrane epithelial Na channel (ENaC) (Fig. 21-5).The reduced rate of Na+ reabsorption diminishes the gradient that facih-tates K+ secretion. K+ secretion by the collecting duct principal cells is a passive phenomenon that depends on and is secondary to the active reabsorption of Na+. 

Hydrochlorothiazide has its proposed site of action at the distal convoluted tubule or, more specifically, at the early portion of the distal tubule. Hydrochlorothiazide inhibits the reabsorption of Na and Cl. It also promotes the reabsorption of Ca back into the blood, but inhibits the re absorption of Mg from the renal tubular fluid. The K-sparing diuretic agents (spironolactone, triamterene, and amiloride) have their site of action in the nephron at the late distal tubule and the collecting duct. These diuretic agents only cause a mild natriuretic effect... 

Many diuretic agents (loop diuretics, thiazides, amiloride, and triamterene) exert their effects on specific membrane transport proteins in renal tubular epithelial cells. Other diuretics exert osmotic effects that prevent water reabsorption (mannitol), inhibit enzymes (acetazolamide), or interfere with hormone receptors in renal epithelial cells (spironolactone). 

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