The Journal of Neuroscience, March 15, 2000, 20(6):2094-2103
Exacerbated Responses to Oxidative Stress by an Na+
Load in Isolated Nerve Terminals: the Role of ATP Depletion and
Rise of [Ca2+]i
Christos
Chinopoulos,
Laszlo
Tretter,
Adrienn
Rozsa, and
Vera
Adam-Vizi
Department of Medical Biochemistry, Neurochemical Group, Semmelweis
University of Medicine, Budapest H-1444, Hungary
We have explored the consequences of a
[Na+]i load and oxidative stress in
isolated nerve terminals. The Na+ load was achieved
by veratridine (5-40 µM), which allows
Na+ entry via a voltage-operated
Na+ channel, and oxidative stress was induced by
hydrogen peroxide (0.1-0.5 mM). Remarkably, neither the
[Na+]i load nor exposure to
H2O2 had any major effect on
[Ca2+]i, mitochondrial membrane
potential (
m), or ATP level. However, the combination of an
Na+ load and oxidative stress caused ATP depletion,
a collapse of 
m, and a progressive deregulation of
[Ca2+]i and
[Na+]i homeostasis. The decrease in
the ATP level was unrelated to an increase in
[Ca2+]i and paralleled the rise in
[Na+]i. The loss of 
m was
prevented in the absence of Ca2+ but unaltered in
the presence of cyclosporin A. We conclude that the increased ATP
consumption by the Na,K-ATPase that results from a modest
[Na+]i load places an additional
demand on mitochondria metabolically compromised by an oxidative
stress, which are unable to produce a sufficient amount of ATP to fuel
the ATP-driven ion pumps. This results in a deregulation of
[Na+]i and
[Ca2+]i, and as a result of the
latter, collapse of 
m. The vicious cycle generated in the
combined presence of Na+ load and oxidative stress
could be an important factor in the neuronal injury produced by
ischemia or excitotoxicity, in which the oxidative insult is
superimposed on a disturbed Na+ homeostasis.
Key words:
oxidative stress; Na+ load; mitochondrial membrane potential; ATP depletion; Na+
deregulation; Ca2+ deregulation
Copyright © 2000 Society for Neuroscience 0270-6474/00/2062094-10$05.00/0