Publication: Brefeldin A influences the cell surface abundance and
intracellular pools of low and high ouabain affinity Na+,
K+-ATPase cx subunit isoforms in articular chondrocytes
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Date
1999
Authors
Mobasheri, A.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The catalytic a isoforms of the Na+, K+-
ATPase and stimuli controlling the plasma membrane
abundance and intracellular distribution of the enzyme
were studied in isolated bovine articular chondrocytes
which have previously been shown to express low and
high ouabain affinity a isoforms (a1 and a 3 respectively;
al>>a3). The Naf, K+-ATPase density of isolated
chondrocyte preparations was quantified by specific 3 ~ -
ouabain binding. Long-term elevation of extracellular
medium [Na+] resulted in a significant (31%; p<0.05)
upregulation of Na+, K+-ATPase density and treatment
with various pharmacological inhibitors (Rrefeldin A,
monensin and cycloheximide) significantly @<0.001)
blocked the upregulation. The subcellular distribution of
the NaC, K+-ATPase a isoforms was examined by
immunofluorescence confocal laser scanning microscopy
which revealed predominantly plasma membrane
immunostaining of a subunits in control chondrocytes.
In Brefeldin A treated chondrocytes exposed to high
[Na+], Na+, K+-ATPase a isoforms accumulated in
juxta-nuclear pools and plasma membrane Na+, K+-
ATPase density monitored by 3~-ouaba inb inding was
significantly down-regulated due to Brefeldin A
mediated disruption of vesicular transport. There was a
marked increase in intracellular a 1 and a3 staining
suggesting that these isoforms are preferentially
upregulated following long-term exposure to high
extracellular [Na+]. The results demonstrate that Na+,
K+-ATPase density in chondrocytes is elevated in
response to increased extracellular [Na+] through de
novo protein synthesis of new pumps containing a 1 and
a 3 isoforms, delivery via the endoplasrnic reticulum-
Golgi complex constitutive secretory pathway and
insertion into the plasma membrane.
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