Effect of Lactacidosis on Cell Volume and Intracellular pH of Astrocytes

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Abstract
Acute traumatic or ischemic cerebral lesions are associated with tissue acidosis leading to cytotoxic brain edema, predominantly affecting astrocytes. Glial swelling from acidosis is believed to be the attempt of cells to maintain a physiological intracellular pH (pHi). However, this concept, potentially important for the development of new treatment strategies for cytotoxic brain edema, has not been validated experimentally. In the present study, cell volume and pHi of astrocytes were measured simultaneously in vitro. Exposure of suspended astrocytes to levels of acidosis found in vivo during ischemia and trauma (pH 6.8–6.2) led to a maximal increase in cell volume of 121.2% after 60 min (n = 5, p < 0.05) and to immediate intracellular acidification close to extracellular levels (pH 6.2, n = 5, p < 0.05). Inhibition of membrane transporters responsible for pHi regulation (0.1 mM amiloride for the Na+/H+ antiporter or 1 mM SITS for HCO3−-dependent transporters) inhibited cell swelling from acidosis but did not affect the profound intracellular acidification. In addition, acidosis-induced cell swelling and intracellular acidification were partly prevented by the addition of ZnCl2 (0.1 mM), an inhibitor of selective proton channels not yet described in astrocytes (n = 5, p < 0.05). In conclusion, these data demonstrate that glial swelling from acidosis is not a cellular response to defend the normal pHi, as had been thought. If these results obtained in vitro are transferable to in vivo conditions, the development of blood-brain barrier-permeable agents for the inhibition of acidosis-induced cytotoxic edema might be therapeutically useful, since they do not enhance intracellular acidosis and thus cell damage.