Depolarization-induced decreases in fluroescence intensity of gastro-intestinal quinacrine-binding nerves

Quinacrine, a fluorescent antimalarial acridine derivative, selectively binds to a population of nerve cell bodies and nerve fibers in Auerbach's plexus and elsewhere in the gut. This quinacrine-binding, as measured by fluorescence intensity, is reduced if the nervous elements are depolarized by high K+ (80--150 MM) or veratridine (5 x 10(-5) M) during quinacrine incubation. A reduction of quinacrine-content in nerve terminals is also seen when depolarization (veratridine) takes place for 2 min after quinacrine-incubation, indicating a release of already bound quinacrine. If terminals are depolarized (high K+ or veratridine) before quinacrine incubation, a reduction of quinacrine content is also seen. The depolarization-induced reduction of quinacrine-binding is blocked by Ca2+-removal and, in the case of veratridine by tetrodotoxin. Our findings suggest that quinacrine binds to a compound that is released by nervous activity. Binding mechanism remains to be elucidated. The possibility that quinacrine visualized purine-rich structures is discussed.