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Abstract
Lactacidosis occurring in cerebral ischemia or trauma is a major mechanism of cytotoxic
brain edema and brain damage. Respective effects of lactacidosis were currently analyzed
in vitro by employment of the murine neuronal cell line, Neuro-2A, in order to obtain
a better understanding of specific mechanisms underlying cell swelling and cell death
in comparison with glial cells. The cells were suspended in a physiological medium
in the presence of lactic acid at increasing concentrations. Levels of acidosis reaching
from pH 6.8-5.6 were obtained while other parameters, such as osmolarity and electrolyte
concentrations, were maintained in the physiological range. Assessment of cell swelling
and cell viability using exclusion of propidium iodide was made by flow cytometry
with employment of an advanced Coulter system. Swelling of Neuro-2A cells commenced
once the pH in the medium was lowered to 6.8 or below. From this level downward, cell
swelling was a function of the severity of acidosis and duration of exposure. For
example, lactacidosis of pH 6.8 or 5.6 lasting 90 min led to an increase in cell volume
to 109.5% or 159.6% of normal, respectively. Viability of the neuronal cells was 85%
under control conditions. It remained in this range down to pH 6.2. At pH 5.6, however,
cell viability decreased in a time-dependent fashion. At 90 min, only 48.9% of the
neuronal cells were viable at pH 5.6. The swelling response and impairment of viability
of the neuronal cells was compared with that of C6 glioma cells. A 60 min exposure
of the glial cells to either pH 6.2 or pH 5.6 led to swelling of only 55% or 65%,
respectively, of the cell volume increase observed in the Neuro-2A cells. In addition,
the glial cells were less vulnerable to lactacidosis as demonstrated by better maintenance
of cell viability. After suspension for 1 h at pH 5.6, only 53.9% of the neuronal
cells were alive, in comparison to 74.1% of the C6 glioma cells. Taken together, the
present findings demonstrate, as former observations on glial cells, that lactacidosis
is a powerful mechanism of cell swelling and cell death in a neuronal cell line. As
in the glial cells, different pH thresholds could be identified, associated either
with cell swelling or a decrease in cell viability. While cell swelling occurred already
at relatively mild levels of acidosis (pH 6.8), viability of the Neuro-2A cells was
decreasing only at pH 5.6, confirming different susceptibilities of cell swelling
and cell death to acidosis. The level of acidosis found to destroy nerve cells in
vitro has been observed in severe forms of cerebral ischemia in vivo, for example
in hyperglycemia.
Keywords
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Publication history
Accepted:
March 18,
1993
Received in revised form:
March 11,
1993
Received:
September 28,
1992
Identification
Copyright
© 1993 Published by Elsevier Inc.
