The amphibian epidermis: distribution of mitochondria-rich cells and the effect of oxytocin.

It is known that the ion-transporting capacity and the permeability to water of amphibian skins vary greatly both between and within species. Furthermore, the extent to which different skins respond to hormonal stimulation of these parameters also shows considerable inter- and intra-specific variation. As a first step towards defining a possible morphological basis for this physiological heterogeneity, we examined different regions of skins from 3 anurans, Bufo bufo, Rana ridibunda and Xenopus laevis, that are species with widely differing habitats. The mitochondria-rich cell population of the epidermis was counted and the epidermal thickness was measured. There were large differences in the mitochondria-rich cell content and in the epidermal thickness of the skins from different species and from different regions of skin from the same animal. In a second set of studies, the same morphological features were examined and, in addition, routine functional parameters were measured to monitor some transport properties of the skins used. The skins also varied considerably with respect to short-circuit current, potential difference, water permeability and sensitivity to oxytocin. Although no apparent relationship was noted between either basal or hormone-stimulated physiological parameters and the morphological features of the individual skins, the striking variation in the density of mitochondria-rich cells in amphibian epidermis merits further studies, including the use of techniques or experimental designs that allow the movement of individual species of ion across the skin to be followed.