Properties of squid axon membrane as revealed by a hydrophobic probe, 2-p-toluidinylnaphthalene-6-sulfonate.

A hydrophobic probe, 2-p-toluidinylnaphthalene-6-sulfonate (TNS), was introduced into the interior of a squid giant axon and fluorescene properties of the TNS-stained axon were examined under illumination with polarized ultraviolet light. A transient reduction in fluorescence was observed when the axon was stimulated electrically. The light waves contributing to this fluorescence change were found to be nearly completely polarized, indicating that the probe molecules in the membrane are highly oriented. The emission spectra of these TNS-stained axons were examined at rest and during nerve excitation. The results obtained are considered to support the view that the process of nerve excitation is accompanied by a transition of the axon membrane from a hydrophobic to a hydrophilic state.