Non-specific inhibition of membrane-ATPase by amiloride: a comparative in vivo and in vitro study with ouabain

The submaxillary duct epithelium, which actively transports Na+ (rabbit) and, in addition, K+ and H+/HCO-/3 (rat), was used as a model epithelium to compare the effects of ouabain and amiloride on transport parameters. 1. Ouabain was only effective from the interstitial side, amiloride, however, only from the luminal side. Amiloride induced effects on transport of the ions were seen within less than 1 s, ouabain effects, however, only after minutes. 2. Ouabain inhibited in a parallel fashion the Na+ transport potential and the Na+-K+-ATPase activity. It had no effect on the Mg2+-ATPase and the HCO-/3-ATPase. 3. Amiloride also inhibited the Na+ transport potential and the Na+-K+-ATPase; however, the Na+ transport potential was significantly more sensitive to amiloride than the Na+-K+-ATPase. 4. Amiloride inhibited in a similar fashion the Na+-K+-ATPase, the Mg2+-ATPase and the HCO-/3-ATPase, but did not influence active HCO-/3 secretion. 5. It is concluded that the amiloride induced effects on the membrane ATPases are non-specific.