Fluorescence Monitoring of Membrane Potentials: the Spatio-Temporal Resolution in Isolated Neurons of Helix pomatia

Using amino-styryl-pyridinium dyes as fluorescent probes we have studied the membrane potential in spheroidal neurons isolated from the circumaesophageal ganglia of the snail Helix pomatia. A spatial resolution of 10 im is attained at a time resolution of 2.5 ms with a typical signal-to-noise ratio of 10/100 mV as referred to an average sensitivity of the probes of 3%/ 100 mV and to a quantum yield of the detector of 0.13. The linear response of fluorescence, the effect of staining, the variation of sampled area and of illumination are characterized.