Thesis defense of Simon Fabiunke

Voltage sensitive dyes have been used as an alternative route to detect membrane potentials. This replaces electrophysiological equipment and allows to study action potentials with optical tools. Changes in fluorescence emission are most commonly translated into changes in transmembrane potentials. In this thesis, it is demonstrated that the emission energy of the fluorescent dye Di-4-ANEPPDHQ is a state variable. Incorporation of the dye in artificIal lipid membranes, where ion transport is obsolete, changes of the emission spectrum as a function of lateral pressure and temperature were detected, as well as in the presence of lateral propagating pulses. It is found that despite the complete absence of transmembrane ion movement, the spectrum shifted about 20 nm at the main transition, which falsifies the Nernst-potential as the origin of the changes in emission. To underline the relevance for action potentials in living systems, the same dye is incorporated into an excitable plant cell to investigate action potentials. There, a very similar blue shift of the emission spectrum is found as in the monolayer pulse experiments. In summary, these experiments showthat Di-4-ANEPPDHQ (presumably all dyes), should be seen as a phase state reporter. This is entirely consistent with the interpretation of the nervous impulse as a propagating state change as has been proposed by others. This interpretation allows to map the state and state changes optically not only of nerves, but even of the entire brain.

Back