SWELLING AND DEATH OF NEURONAL CELLS BY LACTIC-ACID

Lactacidosis occurring in cerebral ischemia or trauma is a major mecha nism of cytotoxic brain edema and brain damage. Respective effects of lactacidosis were currently analyzed in vitro by employment of the mur ine neuronal cell line, Neuro-2A, in order to obtain a better understa nding of specific mechanisms underlying cell swelling and cell death i n comparison with glial cells. The cells were suspended in a physiolog ical medium in the presence of lactic acid at increasing concentration s. Levels of acidosis reaching from pH 6.8-5.6 were obtained while oth er parameters, such as osmolarity and electrolyte concentrations, were maintained in the physiological range. Assessment of cell swelling an d cell viability using exclusion of propidium iodide was made by flow cytometry with employment of an advanced Coulter system. Swelling of N euro-2A cells commenced once the pH in the medium was lowered to 6.8 o r below. From this level downward, cell swelling was a function of the severity of acidosis and duration of exposure. For example, lactacido sis 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 dow n to pH 6.2. At pH 5.6, however, cell viability decreased in a time-de pendent fashion. At 90 min, only 48.9% of the neuronal cells were viab le 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 ex posure of the glial cells to either pH 6.2 or pH 5.6 led to swelling o f only 55% or 65%, respectively, of the cell volume increase observed in the Neuro-2A cells. In addition, the glial cells were less vulnerab le to lactacidosis as demonstrated by better maintenance of cell viabi lity. After suspension for 1 h at pH 5.6, only 53.9% of the neuronal c ells 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, differ ent pH thresholds could be identified, associated either with cell swe lling or a decrease in cell viability. While cell swelling occurred al ready at relatively mild levels of acidosis (pH 6.8), viability of the Neuro-2A cells was decreasing only at pH 5.6, confirming different su sceptibilities 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 hyperglycem ia.