On the mechanism by which 4-aminopyridine occludes quinidine block of the cardiac K+ channel, hKv1.5

Quinidine was employed as an open channel probe in the examination of the kinetic state of 4-aminopyridine blocked channels. Quinidine, in the presence of 0.2-1 mM of 4-aminopyridine, was found to stem charge return and promote partial charge immobilization. Results suggest that the 4-aminopyridine resident in the channel provided an allosteric modulation of the quinidine binding site.