VOLTAGE-SENSITIVE FLUORESCENCE OF AMPHIPHILIC HEMICYANINE DYES IN NEURON MEMBRANE

Fluorescent amphiphilic hemicyanine dyes were adsorbed to the plasma m embrane of isolated Retzius neurons of the leech. Voltage steps were a pplied to the neuron by the patch-clamp technique in whole-cell config uration. The change of fluorescence was observed as induced by the vol tage jump. The relative changes of the excitation spectrum and of the emission spectrum of fluorescence were recorded. The complete set of s pectral data for each dye was fitted by five parameters: shifts of the emission and the excitation spectrum, a change of fluorescence quantu m yield and changes of the widths of the excitation and of the emissio n spectrum. The only common feature for all dyes was a blue-shift of t he excitation spectrum and a drop of the yield when the neuron was sta ined from the outside and a positive voltage was applied to the inside . With respect to the shift of the emission spectrum and the changes o f width qualitatively different results were obtained for different dy es. It is not attempted to assign a physical mechanism - probably a su perposition of several mechanisms - of voltage-sensitivity.