Structure-activity relationships of amiloride and certain of its analogues in relation to the blockade of the Na+/H+ exchange system.

Amiloride and 38 amiloride analogues were tested for their inhibitory action on the Na+/H+ exchanger of chick skeletal muscle cells. The unsubstituted guanidino group of amiloride is essential for the activity of the molecule, since substitution of its results in almost inactive molecules. Selected modification of position 3 and 5 substituents of amiloride have a less dramatic effect on its potency. Substitution of the 5-amino group of amiloride with alkyl or alkenyl groups produced compounds that were up to 140 times more potent than amiloride in inhibiting the Na+/H+ exchanger. Such molecules would appear to be preferable to use in place of amiloride in biochemical and physiological studies of the Na+/H+ exchanger.