Fluorescence Changes in Nerve Induced by Stimulation : Their relation to protein configuration

It was previously assumed, on the basis of changes in the ultraviolet absorption spectrum and of increase in ionizable sulfhydryl groups, that during excitation the proteins of excitable structures undergo some structural rearrangements, and these rearrangements may be similar to those designated by the term transconformation. In the present experiments, it was observed that electrical stimulation of peripheral nerves from rat, guinea pig, frog, and crab causes a decrease in their fluorescence. The peaks of the emission and activation spectra correspond to those attributed to proteins. Denaturing agents, such as urea, were also found to decrease the fluorescence of nerve extracts. It is, therefore, probable that the decrease in fluorescence, associated with the excited state, is due to a change in the configuration of the nerve proteins. The fluorescent method is applicable not only to tissue extracts but allows the observation of surviving nerve fibers before, during, and after stimulation. It showed that fluorescence of the fibers decreases invariably during stimulation and tends to return to the control level during restoration. The reduction in fluorescence is quantitatively related to the number of stimuli received by the nerve.