A new method of monitoring membrane potential in rat hippocampal slices using cyanine voltage-sensitive dyes.

A novel application of voltage-sensitive dyes is described. Hippocampal slices in vitro accumulated voltage-sensitive cyanine dyes under conditions presumed to cause depolarization and hyperpolarization. Increasing extracellular potassium caused a depression of dye uptake that correlated linearly with the membrane potential calculated from the Goldman equation. Veratrine depressed dye uptake, and this effect was blocked by addition of tetrodotoxin or removal of extracellular sodium. Ouabain also depressed dye uptake. Conversely, hyperpolarizing conditions using reduced extracellular sodium caused increased dye uptake. These results support a voltage-dependent mechanism for the uptake of cyanine dyes in hippocampal slices. Application of this phenomenon as an alternative to 2-deoxyglucose autoradiography for mapping neuronal activity will be presented.