Inhibition of Na+/H+ Antiport Activity in Sugar Beet Tonoplast by Analogs of Amiloride

Abstract
The effects of amiloride and a series of amiloride analogs have been tested on the Na+/H+ antiport activity in intact vacuoles and tonoplast vesicles isolated from sugar beet [Beta vulgaris] cell suspension cultures. There is a competitive interaction between amiloride analogs and sodium. Substitution of one or both H-atoms of the 5-amino group of amiloride (apparent Ki about 150 micromolar) resulted in a 3- to 200-fold increase in inhibitory potency of the antiport activity.