Staining of Living Merkel Cells with FM Dyes

Summary

Live Merkel cells are known to incorporate a fluorescent dye, quinacrine (3,3′,4′,5,7-pentahydroxyflavone). Quinacrine fluorescence in the cells is, however, quickly lost and quinacrine-stained Merkel cells become difficult to identify in tissue culture. To find dyes that stay in the cells for a long period of time, we tested many fluorescent dyes and found that FMI-43 (N-(3triethylammoniumpropyl)-4-(4-(dibutylamino)-styryl)pyridinium dibromide) is a useful marker for live Merkel cells. In the rat footpad skin, FM1-43 was revealed to stain most of the live Merkel cells that were already stained with quinacrine. Merkel cells in sinus hair follicles were also stained with FM1-43 dye. The fluorescence intensity of the FM dye was stronger than that of quinacrine, and the shape of the cells was more distinct in the FMI-43-stained cells. We thus conclude that the FM dye is a powerful tool for tracing live Merkel cells in in vitro experiments. Moreover, the finding that Merkel cells incorporate the FM dye suggests that vesicles in Merkel cells are likely to represent recycling in a manner similar to those in neurons and secretory cells.