Chronic regulation of transepithelial na+ transport by the rate of
apical na+ entry.
Rokaw, Michael D., Erdal Sarac, Eric Lechman, Michael West, Joseph
Angeski, John P. Johnson, and Mark L. Zeidel.
Laboratory of Epithelial Cell Biology, Renal - Electrolyte
Division, University of Pittsburgh Medical Center and Medical
Service, Oakland VA Medical Center, Pittsburgh, PA
APStracts 2:0315C, 1995.
In several settings in vivo, prolonged inhibition of apical Na+ entry
reduces and prolonged stimulation of apical entry enhances the
ability of renal epithelial cells to reabsorb Na+, an important
feature of the load-dependent regulation of renal tubular Na+
transport. To model this load dependency, apical Na+ entry was
inhibited or stimulated for 18h in A6 cells and vectorial transport
measured as short circuit current (ISC) across monolayers on filter
-bottom structures. Basal amiloride-sensitive ISC represents the
activity of apical Na+ channels, while ISC following permeabilization
of the apical membrane to cations with nystatin represents maximal
activity of the basolateral Na/K-ATPase. Chronic inhibition of apical
Na+ entry by 18h apical exposure to amiloride or replacement of
apical Na+ with tetramethylammonium (TMA+) followed by washing and
restoration of normal apical medium revealed a persistent decrease in
ISC which remained despite exposure to nystatin. Both basal and
nystatin-stimulated ISC recovered progressively following restoration
of normal apical medium. By contrast, chronic stimulation of apical
Na+ entry by short circuiting the epithelium increased ISC in the
absence and presence of nystatin, indicating upregulation of both
apical Na+ channels and basolateral Na/K-ATPase. Basolateral
equilibrium 3H-ouabain binding was reduced to 67 +/- 5% in TMA+ vs
control cells, while values in 18h short circuited cells increased by
42 19%. The results demonstrate that load dependency of tubular Na+
transport can be modeled in vitro and indicate that the regulation of
Na/K-ATPase observed in these studies occurs in part by changes in
the density of functional transporter proteins within the basolateral
membrane.
Received 8 June 1995; accepted in final form 10 August 1995.
APS Manuscript Number C321-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.