The mitochondria-rich cell of frog skin as hormone-sensitive "shunt-path".

Further investigations about the role of the mitochondria-rich cell (MR cell) in hormone-mediated transport regulation in the epithelium of frog skin brought the following results: Unlike toad bladder, in frog skin the spontaneous potential difference cannot be reversed when Na transport is blocked. A similar situation is obtained when, in addition to transport-blockade, one applies a chemical gradient for chloride to the epithelium. Under these conditions we found that in the intact preparation as well as in the separated epithelium: (i) the reversed current (RC) is linearly related to the number of MR cells; (ii) RC is mainly carried by a passive, transcellular chloride flux inwards and (iii) RC is sensitive to nor-adrenaline (10(-7) M). The beta-blocker propranolol abolishes this effect. We propose that the MR cells are the sites of transepithelial shunt-path and that this chloride flux is transcellular. As it is hormone sensitive, it could be an important regulatory instrument for the regulation of overall salt transport (internal shorting).