Interaction of a fluorescent probe with acetylcholine-activated synaptic membrane

Abstract

GRÜNHAGEN and Changeux have shown^1,2 that Torpedo membrane fragments stained with the antimalarial, quinacrine, show a rapid increase in fluorescence after mixing with cholinergic agonists (see ref. 3). These authors suggest that the fluorescence intensity of quinacrine associated with cholinergic receptors increases during the transition of the receptor from its resting to its active state. We report here an electrophysiological analysis of the kinetic behaviour of the postsynaptic membrane of intact vertebrate muscle fibres treated with quinacrine. The kinetic data from the fluorescence and electrophysiological experiments show remarkable parallels, and we suggest that both experimental procedures reveal the binding of quinacrine to the activated receptor.