Intracellular distribution of lipophilic fluorescent probes in mammalian cells

The intracellular distribution of several hydrophobic fluorescent probes (1,6-diphenyl-1,3,5-hexatriene (DPH), perylene, and $\text{2-p-}\text{toluidinyl-6-naphthalene}$ sulfonate (TNS)) in mouse lymphocytes and a fibroblast cell line was examined using radiolabeled fluorescent probes and the technique of high resolution EM autoradiography. Following a short term incubation, DPH and perylene were found largely internalized in cells, while TNS was localized predominantly at the cell surface. These findings suggest that fluorescence polarization studies using such probes with intact cells do not necessarily monitor only the cell surface membrane and must be interpreted with caution.