AJP - Renal Physiology, Vol 249, Issue 5 662-F671, Copyright © 1985 by American Physiological Society
Dependence of intracellular Na+ concentration on apical and basolateral membrane Na+ influx in frog skin
J. S. Stoddard and S. I. Helman
An isotopic method was developed to measure the intracellular Na+ content
of the transepithelial Na+ transport pool of frog skin. Isolated epithelia
(no corium) were labeled with 24Na either asymmetrically, from apical (Aa)
or basolateral (Ab) solutions, or symmetrically (Aab). Transport pool Na+
could be identified from the kinetics of washout of 24Na carried out in the
presence of 1 mM ouabain, 100 microM amiloride, and 1 mM furosemide that
served to trap cold Na+ and 24Na within the transport pool. In control
epithelia, Aab averaged 64.1 neq/cm2 (13.9 mM), and maximal inhibition of
apical membrane Na+ entry with 100 microM amiloride caused Aab to decrease
to 24.3 neq/cm2 (5.3 mM). Ouabain caused Aab to increase markedly to 303
neq/cm2 in 30 min, whereas amiloride inhibition of apical membrane Na+
entry reduced markedly the rate of increase of Aab caused by ouabain (7.3
neq X cm-2 X min-1 in control and 1.7 neq X cm-2 X min-1 in the presence of
amiloride). These data, in part, confirmed the existence of an important
basolateral membrane permeability to Na+ that was measured in separate
studies of the bidirectional 24Na fluxes at the basolateral membranes of
the cells. Both sets of data were supportive of the idea that a significant
Na+ recycling exists at the basolateral membranes of the cells that
contributes to the Na+ load on the pump and Na+ recycling participates in
the regulation of the Na+ concentration of the Na+ transport pool of these
epithelial cells.
