Use of the MTT assay for estimating toxicity in primary astrocyte and C6 glioma cell cultures.

Primary cultures of rat cortical astrocytes were exposed to 25 neurotoxic and non-neurotoxic compounds for 24 hr over a concentration range of 0.001 to 1000 mug/ml and the effects were quantified using the MTT assay. EC(50) values were obtained for nine of the compounds in the tested range, while increases in MTT conversion were seen at sub-cytotoxic concentrations for 12 compounds. The concentrations causing activation of this system were found, with some exceptions (notably organotin compounds) to be similar to those previously reported to cause increases in expression of the astrocyte marker glial fibrillary acidic protein. MTT conversion was also measured in the C6 cell line and, with some exceptions, the response to toxicants was found to be the same as that in the primary cultures of astrocytes. However, this was only the case when the C6 cells were pretreated for 48 hr with 0.5 mM dibutyryl cyclic AMP. This study represents the first direct comparison between primary astrocytes and C6 cells using a broad range of chemical neurotoxicants.