Mitochondria-rich cells in gills and skin of an African lungfish, Protopterus annectens

Abstract We used scanning electron microscopy, the vi- tal dye DASPEI and an antibody to the inner mitochon- drial membrane to study the presence and localisation of mitochondria-rich cells in the gills and skin (opercular, dorsal and ventral) of the lungfish Protopterus annectens in its free-swimming conditions and at the beginning of aestivation. In the free-swimming period, the gills were short and thick and the pavement cells were extremely large (30–40 μm). The mitochondria-rich cells, which were distributed in the secondary and primary epitheli- um, occurred as two morphologically different types, i.e. elongated and oval, similar to the α and β chloride cells of fresh water teleosts. In the skin, only one type of mi- tochondria-rich cells was found, resembling the α chlo- ride cells. All the mitochondria-rich cells distributed in the gills and skin were labelled with anti Ca2+-ATPase serum indicating the possible uptake of Ca2+ at freshwa- ter chloride cell level. At the start of aestivation, the skin and gills were covered by a thick layer of mucus and the epithelium of the gills was reduced. The mitochondria- rich cells were almost completely covered by the pave- ment cells.