Mitochondria-rich cells of frog skin in transport mechanisms: morphological and kinetic studies on transepithelial excretion of methylene blue.

The following study combines histological observations on the localization and density of mitochondria-rich cells with a kinetic study of the part played by these cells in transport phenomena. In the ventral skin, mitochondria-rich cells and granular cells are equally abundant in the first living cell layer. The mitochondria-rich cells were shown to excrete methylene blue [3,9-bis-(dimethylamino)-phenozathionum chloride]. A kinetic study of this excretion across the isolated epithelium of Rana esculenta skin showed that the mechanism of the excretion was a saturable one. An important fraction of methylene blue excretion depends on the absorption of sodium; the absence of this ion, or the inhibition of its transport by ouabain or amiloride, inhibits the excretion of the organic base. The mitochondria-rich cells, however, do not appear to play a determining role in sodium transport.