Mitochondria-rich cells in anuran Amphibia: chloride conductance and regional distribution over the body surface

The distribution and density (D-mrc) of mitochondria-rich cells (MR cells) in skin epithelium, were determined over the whole body surface in nine spe cies of anuran Amphibia that live in a variety of habitats. It was found th at the more terrestrial species (beginning with Hyla arborea) have a higher density of MR cells in their pelvic region. In the skin of aquatic (Xenopu s laevis) or fossorial (Pelobates syriacus) species, D-mrc is evenly distri buted over the whole body surface. In dorsal skin pieces of H. arborea that lack detectable MR cells, transepithelial voltage activation did not induc e Cl- conductance as it did in ventral pieces. Skins from Bufo viridis and X. laevis, both have MR cells in their skin, differ markedly in their bioph ysical properties: a Cl- specific current conductance is predominant in the skin epithelium of B. viridis, and is absent in X. laevis. In the latter, anionic conductance is due to glandular secretion. The biophysical properti es cannot therefore be related solely to the presence or density of MR cell s. Mitochondria-rich cells are sites of Cl- conductance across the skin of those amphibians that show this property, but must have different function( s) in other species. It is suggested that the specific zonal distribution o f MR cells in the species that were examined in this study could be due to ion exchange activity and water conservation in more terrestrial environmen ts. (C) 2000 Elsevier Science Inc. All rights reserved.