Merkel cell distribution in the epidermis as determined by quinacrine fluorescence

The Merkel cell distribution in the basal epidermis of amphibian and mammalian skin was visualized in whole mounts by means of quinacrine fluorescence. In most cases only the isolated epidermis was viewed following dermal-epidermal separation. Tadpole tentacles contained numerous quinacrine fluorescent cells (QFC) 25–40 μm apart. Groups of 2–4 QFC were found around the gland openings in frog epidermis but not in salamander epidermis where the QFC were irregularly scattered 40–100 μm apart. In the rat, ring-like clusters of a few to 200 or more QFC were distributed across the basal epidermis of trunk skin (at touch domes or Haarscheiben), eyelid, ear, nose, and whisker pad. The ridged (glabrous) skin of the nose and footpad contained numerous QFC that appeared to follow the contours of the epidermal ridges. The isolated external root sheath of rat vibrissae contained an upper cylindrical cuff of several hundred QFC; enzymatic dissociation of these sheaths produced individually isolated as well as small clusters of fluorescent and non-fluorescent cells. Electron-microscopic examination of several of these cells confirmed that the fluorescent ones are Merkel cells, identified by the presence of characteristic dense-cored granules; in contrast, the non-fluorescent cells lack this ultrastructural feature.