Occludin and hydromineral balance in Xenopus laevis.
Morphological, biochemical and histochemical components of mitochondria-rich (MR) cells of skin epithelium of Xenopus laevis (Daudin) were investigated after acclimation in distilled water (DW) and mild solutions (50 mmol/l) of either NaCl or KCl for over 10 days. The animals readily acclimated to NaCl, but approximately 50% of the animals died in the KCl solution. Electrophysiological measurements confirmed the poor transport properties of skin in all conditions. Silver staining and exposure to methylene blue (MB) have shown that two types of MR cells can be distinguished, especially after KCl acclimation. Immunohistochemistry with the use of anti-band 3 polyclonal and anti H+-ATPase monoclonal antibodies demonstrated that band 3 and H+-ATPase enzymes were localized in MR cells in all conditions. H+-ATPase was greatly reduced during NaCl acclimation as verified with SDS gel electrophoresis. Intensity of the immunohistochemical staining differed between the various conditions of acclimation. Histochemical localization of carbonic anhydrase and alkaline phosphatase activities was more intense during NaCl acclimation. Morphological changes were also observed between the various acclimation conditions. The present findings substantiate the existence of at least two forms of MR cells in Xenopus skin epithelium but their functional significance remains to be established.