The role of mitochondria-rich cells in sodium transport across amphibian skin.

The possible participation of mitochondria-rich cells in transepithelial Na+ transport across frog skin under "physiological conditions" (low apical [Na+], open circuited) was analysed by recording electrophysiological parameters from principal cells with intracellular microelectrodes and using measurement of Rb+ uptake into the epithelial cells from the serosal side via the Na+/K+-ATPase. It was observed that transport perturbation with amiloride induced changes in the apical potential difference and fractional apical resistance in principal cells, observations which are compatible with the notion that the essential fraction of transcellular current flow occurs across these cells. Amiloride-inhibitable uptake of Rb+ was also restricted to principal cells, the amount being about equivalent to the predicted rate of K+ recycling via the Na+/K+-ATPase. The results indicate that principal cells are responsible for transepithelial Na+ transport irrespective of the experimental conditions. Flow of Na+ across mitochondria-rich cells appears to be negligible.