Styryl dyes stain synaptic vesicles in an activity-dependent fashion. The dyes are virtually non-fluorescent in aqueous solution, but become brightly fluorescent upon insertion into the plasma membrane. During endocytosis following neuronal stimulation, the dyes become trapped in vesicles. After free dye is removed from the cell surface by washing, the remaining fluorescence is proportional to the number of newly formed endocytic vesicles. During exocytosis, the dyes are released to the aqueous medium, causing a decrease in fluorescent signal. As a result, the change in fluorescence intensity reflects the amount of endocytosis and exocytosis occuring during synaptic activity. The rate of fluorescence increase during endocytosis (on-rate) and the rate of fluorescence decrease during exocytosis (off-rate) varies from dye to dye. In general, dyes with longer lipophilic tails and more double bonds have a faster on-rate and slower off-rate. AM dyes have an additional amine group and therefore tend to be more water soluble than their FM dye counterparts, resulting in a slower on-rate and faster off-rate.
Bestellinformation: Sulforhodamine 101 is also available separately.