AJP - Cell Physiology, Vol 232, Issue 1 67-C75, Copyright © 1977 by American Physiological Society
Effect of inhibitors on transepithelial efflux of Na and nonelectrolytes in frog skin
T. U. Biber and T. L. Mullen
The transepithelial efflux of Na and several nonelectrolytes (mannitol,
sucrose, and polyethylene glycol 900) were measured in the isolated frog
skin under short-circuited conditions in chambers that had been specially
designed to avoid edge damage. Ouabain (10(-3) and 10(-4) M) caused a
dramatic increase in the efflux of Na, whereas the efflux of
nonelectrolytes showed only a slight alteration. The efflux of Na increased
after the application of dinitrophenol (10(-4) M), whereas the efflux of
nonelectrolytes remained constant. Amiloride (10(-3) M) caused large
variations in the efflux of Na, whereas the efflux of nonelectrolytes
remained unchanged. The results provide evidence that these inhibitors do
not alter the permeability of the paracellular pathway and that the total
transepithelial efflux of Na or at least a very large portion of it, and
possibly also the transepithelial efflux of Cl, proceeds via a
transcellular pathway and not a paracellular pathway as has been widely
accepted. The data further suggest that the Na proceeding via this pathway
interacts directly or indirectly with the active transport step.
