On the presence of high glycogen concentration and intermediate filaments in the flat cells of the electroreceptive epidermis of mormyrid fish.
The cytoplasm of the flat cells of the electroreceptive epidermis of Mormyrids was examined in the light and the electron microscope, in order to reveal the presence of glycogen and to study its distribution. In the electroreceptive epidermis, which consists of three layers, the periodic acid Schiff reaction used to stain polysaccharides is strongly positive in the superficial polyhedral cells and in the flat cells of the intermediate layer. Polysaccharides are absent in the basal polyhedral cells. Pre-incubation with alpha-amylase shows that glycogen is present only in the intermediate cell layer. In the electron microscope, after reaction with periodic acid, thiocarbohydrazide and silver proteinate, glycogen is seen in the form of rosettes of monoparticles. These rosettes occupy both the central region of the cytoplasm of these cells, and the more peripheral parts, where alignments of desmosomes are found. In the cytoplasm of certain flat cells, the rosettes are grouped to form accumulations of glycogen which cover several mu2. Observation in the electron microscope reveals that in addition to glycogen, these cells contain tonofilaments or intermediate filaments, common to epithelial cells, which may group themselves in bundles. Glycogen and the intermediate filaments are thus the principal constituents of the cytoplasm of the flat cells of the electroreceptive epidermis of Mormyrids. The possible role of the filaments, and especially of the glycogen which is a polysaccharide high in energy, in the flat cells which apparently have a low metabolic rate, is discussed.