The determination of ion concentrations in cells - in particular in neurons - is very important for understanding cell
function and life. Calcium is an ubiquitous messenger in almost all cell types. Fluorescence lifetime imaging (FLIM) can
be of advantage over intensity based fluorescence microscopy, when comparisons between micro-domains of one cell or
between different cells of one cell type are performed. Several organic chromophores have been tested in cuvette
experiments as well as in living cells and cell tissue with respect to their applicability in FLIM studies. The calcium
concentration changes in several cell types were investigated by FLIM with two-photon excitation.
Several voltage sensitive dyes and other dyes with high membrane affinity have been investigated with respect to their
use in multiphoton fluorescence microscopy with special emphasis on fluorescence lifetime imaging. The fluorescence
decay behavior in several cell types and in the retina, the dye distribution pattern and changes upon external stimuli are
found to be very different.