Azidoacridines as photoaffinity probes for ionic channels in excitable membranes

Quinacrine and a photoactivatable congener, quinacrine azide, were applied to the intracellular membrane surface of voltage-clamped squid giant axons using internal perfusion techniques. Both compounds were found to reversibly block voltage-dependent sodium channels under dark conditions. Potassium channels were blocked to a lesser extent. Upon irradiation an irreversible block of sodium channels developed with quinacrine azide, but not with quinacrine. Quinacrine azide may thus represent a class of useful photoaffinity probes of voltage-dependent ionic channels.