Fluorescent amphiphilic hemicyanine dyes were adsorbed to the plasma membrane of isolated Retzius neurons of the leech. Voltage steps were applied to the neuron by the patch-clamp technique in whole-cell configuration. The change of fluorescence was observed as induced by the voltage jump. The relative changes of the excitation spectrum and of the emission spectrum of fluorescence were recorded. The complete set of spectral data for each dye was fitted by five parameters: shifts of the emission and the excitation spectrum, a change of fluorescence quantum yield and changes of the widths of the excitation and of the emission spectrum. The only common feature for all dyes was a blue-shift of the excitation spectrum and a drop of the yield when the neuron was stained from the outside and a positive voltage was applied to the inside. With respect to the shift of the emission spectrum and the changes of width qualitatively different results were obtained for different dyes. It is not attempted to assign a physical mechanism--probably a superposition of several mechanisms--of voltage-sensitivity.
Animals Cell Membrane