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-rENaC expressed in
Xenopus oocytes
Department of Physiology and Biophysics, University of Alabama, Birmingham, Alabama, 35294-0005
The hypothesis
that amiloride-sensitive Na+
channels (ENaC) are involved in cell volume regulation was tested.
Anisosmotic ND-20 media (ranging from 70 to 450 mosM) were used to
superfuse Xenopus oocytes expressing
-rat ENaC (-rENaC). Whole cell currents were
reversibly dependent on external osmolarity. Under conditions of
swelling (70 mosM) or shrinkage (450 mosM), current amplitude decreased
and increased, respectively. In contrast, there was no change in
current amplitude of H2O-injected
oocytes to the above osmotic insults. Currents recorded from
-rENaC-injected oocytes were not sensitive to external
Cl
concentration or to the
K+ channel inhibitor
BaCl2. They were sensitive to
amiloride. The concentration of amiloride necessary to inhibit one-half
of the maximal rENaC current expressed in oocytes
(Ki; apparent
dissociation constant) decreased in swollen cells and increased in
shrunken oocytes. The osmotic pressure-induced
Na+ currents showed properties
similar to those of stretch-activated channels, including inhibition by
Gd3+ and
La3+, and decreased selectivity
for Na+.
-rENaC-expressing oocytes maintained a nearly constant cell volume in hypertonic ND-20. The present study is the first
demonstration that -rENaC heterologously expressed in
Xenopus oocytes may contribute to
oocyte volume regulation following shrinkage.
rat epithelial sodium channel; mechanosensation; cell volume; amiloride; voltage clamp
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