Effect of mild and moderate hypothermia on the acidosis-induced swelling of glial cells.

The effect of mild (32 degrees C) and moderate (27 degrees C) hypothermia was analyzed on the cell volume and intracellular pH (pHi) of C6 glioma cells at normal pH and during lactacidosis at pH 6.2 in vitro. The cells were suspended in an incubation chamber under continuous control of pH, PO2 and temperature. Cell swelling was quantified by an advanced Coulter-system. pHi was measured by flow cytometry using the fluorescent dye bis-carboxyethyl carboxyfluorescein (BCECF). Following a control period at 37 degrees C, the ambient temperature was decreased to 32 degrees C for 30 min, and subsequently to 27 degrees C for another 30 min. Hypothermia alone led to an immediate and significant cell volume increase of 107.3 +/- 0.4% (mean +/- SEM) of control after 30 min at 32 degrees C, and further swelling to 110.5 +/- 0.9% after 30 min at 27 degrees C. Yet, hypothermia (27 degrees C) afforded partial protection against the acidosis-induced cell swelling at pH 6.2, which was reaching to 120.4 +/- 0.9% in the normothermic control group after 60 min, while only to 111.3 +/- 0.9% at 27 degrees C. Hypothermia, however, was associated with a more pronounced decrease of the pHi during acidosis (6.3 +/- 0.04) as compared to that of the normothermic control falling then to 6.5 +/- 0.03. The results demonstrate that mild and moderate hypothermia induce glial cell swelling, but simultaneously inhibit cell swelling from acidosis. The protection against cell swelling, however, has its price as indicated by the enhancement of the intracellular acidification.