EFFLUX OF ENDOGENOUS PROTEIN FROM NON‐MYELINATED OLFACTORY NERVE AS MONITORED BY TRYPTOPHAN FLUORESCENCE

Endogenous protein was lost from the olfactory nerve of the garfish ( Lepisosteus osseus ) when the excised but excitable nerve was bathed with normal physiological solution. The protein could be detected by its fluorescence at 340 nm when excited at 280 nm. The relative concentrations were expressed in terms of an equivalent fluorescence from a standard solution of tryptophan. From an initial fluorescence, equivalent to 5 × 10 −10 mol of tryptophan/mg of nerve washed out during each 10 min, the efflux may decline slowly in rate to 10 −11 mol/mg per 10 min. Depolarizing direct current or a several‐fold increase of the concentration of KCl in the bathing solution might transiently double the rate of efflux above the resting rate during continuous monitoring of the fluorescence intensity. Changes in concentrations of external KCl, glucose or sucrose, in ionic strength (at constant osmolality), or in osmolality all produced a transient increase of fluorescence in the effluent from the nerve. An increase followed both introduction of the experimental solution and the return to the control solution. We interpreted the increase in intensity of fluorescence of the washout solution to indicate an increase in concentration of an intrinsic specific protein washed from the nerve. By electrophoresis, a single acidic fluorescent protein band was observed travelling with the marking dye. Chromatographic fractionation on Sephadex suggested a mol. wt. in excess of 100,000.