Brefeldin a inhibition of apical na+ channels in epithelia.
Fisher, Richard S., F. Gregory Grillo, Sarah Sariban-Sohraby, Richard
S. Fisher, F. Gregory Grillo, Sarah Sariban-Sohraby.
Department of Nephrology, Walter Reed Army Institute of Research,
Washington, DC 20307-5100, Tel: (202) 576-3542, FAX: (202) 576-0703
and Laboratoire de Physiopathologie, Universit[acute]e Libre de
Bruxelles, Campus Erasme, Batiment E2.4.111, Route de Lennik 808,
1070 Bruxelles, Belgium,
APStracts 2:0316C, 1995.
Brefeldin A (BFA) is used to probe trafficking of proteins through the
central vacuolar system (CVS) in a variety of cells. Transepithelial
Na+ transport by high resistance epithelia, such as A6 cultured
cells, is inhibited by BFA. Apical Na+ channels, as well as
basolateral pumps and K+ channels, are complex proteins which
probably traverse the CVS for routing to the plasma membrane. BFA
(5[mu]g/ml) decreases transepithelial Na+ current near zero and
increases resistance reversibly after 4 h. Longer exposures were
toxic. When tissues were treated for 20 h with 0.2 [mu]g/ml BFA, Na+
transport also was reversibly inhibited. Using noise analysis, we
found that BFA drastically reduces apical Na+ channel density. Single
channel current increased consistent with cell hyperpolarization.
After apical permeabilization with nystatin, changes of
transepithelial current reflect changes of basolateral membrane
transport. Transport at this membrane was inhibited by ouabain and
cycloheximide, but not by BFA. After BFA, aldosterone was ineffective
suggesting that an intact CVS is required for stimulation by this
hormone. Thus, BFA inhibition of Na+ transport is localized at the
apical membrane. Implications for channel turnover as a mechanism for
regulating the Na+ transport rate are discussed.
Received 9 February 1995; accepted in final form 28 June 1995.
APS Manuscript Number C70-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.