Effects of lactacidosis on volume and viability of glial cells

The effect of lactacidosis was analyzed in vitro by employment of C 6 glioma cells and astrocytes from primary culture. The cells were suspended in an incubation chamber under continuous control of pH, temperature and pO2. Cell swelling and viability were quantified by flow cytometry using propidium iodide for staining of dead cells. After a control period, the pH of the suspension medium was titrated to levels between pH 6.8 down to 4.2 by addition of isotonic lactic acid. Acidification below pH 6.8 led to an immediate swelling of C 6 glioma cells as well as of astrocytes. The degree of cell swelling was related to the decrease in pH and the duration of exposure. For instance, lactacidosis of 60 min at pH 6.2 resulted in an increase of glial volume to 124.5 +/- 4.6%, while pH 4.2 in an increase to 190.9 +/- 8.4%. Cell viability remained unchanged down to pH 6.2. At pH 5.6 and below viability decreased in relation to the severity of acidosis. When sulfuric acid was used, the extent of cell swelling at pH 5.6 was only 50% of what was found by addition of lactic acid, whereas cell viability was not differently affected. The results demonstrate a specific efficacy of lactic acid to induce glial swelling, which might be due to a cellular accumulation of the compound.