Effects of aldosterone on rat collecting tubule N-ethylmaleimide-sensitive adenosine triphosphatase.

Acidification in the collecting tubule is thought to be mediated by a proton-translocating adenosine triphosphatase (ATPase), and is modulated by aldosterone. Using an enzymatic microassay, we measured N-ethylmaleimide (NEM)-sensitive ATPase activity in isolated tubules obtained from control rats and rats receiving aldosterone by osmotic minipumps (5 micrograms/100 gm/day for 7 days). In control animals, enzyme activity was higher in cortical than in outer medullary collecting tubules (259 +/- 36 vs. 111 +/- 16 pmol/mm/hr, P less than 0.005, respectively). Prolonged aldosterone administration resulted in an increase in enzyme activity in the outer medullary collecting tubule (274 +/- 39 pmol/mm/hr, P less than 0.005), with no change in the cortical collecting tubule (255 +/- 47 pmol/mm/hr). These findings suggest that prolonged enhancement of acidification by mineralocorticoids is mediated by different mechanisms in the two segments of the rat collecting tubule. Whereas in the outer medullary segment an increase in the activity of NEM-sensitive ATPase facilitates the chronic enhancement in acidification, high basal enzyme activity in the cortical segment and institution of favorable voltage condition by mineralocorticoid treatment may obviate the need to increase enzyme activity.