The therapeutic efficacy of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), an isomer of the intracellular messenger IP3, was analyzed for cytotoxic swelling and damage of glial cells in vitro from lactacidosis or glutamate. Lactacidosis and the interstitial accumulation of glutamate are prominent sequelae in ischemic or traumatic brain tissue. C6 glioma cells harvested from culture and suspended in a physiological medium were either exposed to pH 5.0 by administration of lactic acid, or to 1 mM glutamate at normal pH. Cell swelling and viability were quantified by blood flow cytometry. Addition of alpha-trinositol (3 mM) under control conditions at pH 7.4 resulted in transient cell shrinking to 96.5 +/- 1.3% of control within 3 min (p < 0.05). Lactacidosis of pH 5.0 led to an increase in cell volume to 139.7 +/- 1.3% within 20 min, whereas alpha-trinositol reduced the swelling response by approximately 25% (p < 0.01). In addition, cell viability was severely affected at pH 5.0 amounting to only 53.8 +/- 3.1% after 60 min. alpha-Trinositol was found to markedly improve cell viability; at 60 min 70.2 +/- 1.6% of the cells were still viable (p < 0.01). Addition of glutamate (1 mM) led to a steady increase in cell size, reaching 110% of control after 120 min, irrespective of wether alpha-trinositol was present or not. The attenuation of cell swelling may be attributed to an interference with pH-regulatory mechanisms, such as the Na+/H(+)-antiporter, while protection of cell viability might be caused be effects of alpha-trinositol on Ca(2+)-overload. On the other hand, the increase in cell volume by glutamate associated with its intracellular uptake was not influenced by alpha-trinositol.