AJP - Renal Physiology, Vol 266, Issue 3 367-F374, Copyright © 1994 by American Physiological Society
pHi determines rate of sodium transport in frog skin: results of a new method to determine pHi
R. Rick
Department of Physiology and Biophysics, University of Alabama at Birmingham 35294.
The pH of the isolated frog skin epithelium was determined on a cellular
and subcellular level based on the distribution of a weak organic acid,
4-bromobenzoic acid. The indicator is detectable by X-ray microanalysis due
to the presence of an element label. The results show that the pH of
principal cells, but not the Na concentration, is closely correlated with
the rate of transepithelial Na transport. Acidification leads to an
inhibition of Na transport, regardless of whether the change was
spontaneous or experimentally induced. Under the conditions of this study,
the pH of principal cells was not well regulated. At a bath pH of 7.0,
large pH differences between the cell layers were detectable. In
mitochondria-rich cells, the pH was a function of the intracellular Cl
concentration but not the Na transport rate. The cytoplasmic pH
consistently exceeded the nuclear pH. The nuclear-cytoplasmic pH
differential in principal cells amounted to 0.3 pH units, which is
equivalent to a nuclear potential of -17 mV. The results support the view
that the intracellular pH (pHi) is an important regulator of
transepithelial Na transport. Regulation is primarily achieved at the level
of the apical Na channel, making the Na influx the rate-limiting step in Na
reabsorption.
