Moulting in Rana esculenta: development of mitochondria-rich cells, morphological changes of the epithelium and sodium transport.

The present study concerns moulting of the skin in Rana esculenta in vivo and in vitro. The evolution of mitochondria-rich cells (MRC) and changes in the epithelium during moulting were followed. The greater part of the MRC are lost during moulting, either because they remain attached to the old stratum corneum or because they are left in contact with the external medium and degenerate. The cells thus lost leave deep impressions in the new stratum corneum which disappear progressively. Before an MRC is shed, a cell of the stratum intermedium contacting it differentiates to form a new MRC to replace the old. Isolation of the skin triggers moulting in the excised pieces. This moulting does not cause changes in the short-circuit current or in the transepithelial resistance. Aldosterone (10(-6) M) added in vitro to the serous side appeared to facilitate the detachment of the slough, however, no clear-cut moult-inducing effect of the hormone was seen.