Quinacrine fluorescence of Merkel cells in Xenopus laevis.

It has been shown by electron microscopy that, in Xenopus laevis, Merkel cells are usually situated near the ducts of the skin glands. Cells which fluorescence in ultra-violet light after treatment of the skin with quinacrine can be identified with these Merkel cells by their position, shape and size. The method indicates the presence of purine nucleotides, probably ATP. This result is consistent with the view that "large opaque vesicles" are sites of ATP storage.