EVALUATION OF NERVE-CELL TOXICITY INVITRO BY ELECTROPHYSIOLOGICAL AND BIOCHEMICAL METHODS

The acute toxicity of the first nine standard chemicals in the Multicentre Evaluation of In Vitro Cytotoxicity Tests (MEIC) programme was evaluated in the NG108-15 neuroblastoma cell line by monitoring changes in cell resting membrane potential (RMP) and by using the MTT assay to measure cell viability. Cells were differentiated with dibutyryl-cAMP and then exposed to different concentrations of the chemicals for 1 hr or 24 hr. At each concentration and time point, RMPs were measured from about 30 differentiated cells and MTT assays were performed on parallel cultures. IC50 values were obtained from linear regression analysis. The results showed that the IC50s from MTT assays correlated closely with those from RMP measurements (r = 0.983 for 1 hr exposure; r = 0.933 for 24 hr exposure). IC50s of amitriptyline and diazepam were 0.1-1.9 mm; alcoholic compounds (isopropanol, ethylene glycol, ethanol and methanol) had IC50s from 121.5 mm to 3731.9 mm; paracetamol, aspirin and ferrous sulphate had intermediate cytotoxicity (IC50 2.6-53.5 mm). IC50s decreased markedly with increased exposure time. RMP is expected to be a sensitive indicator of the health of nerve cells; however, its measurement in a large number of cells is laborious. MTT assays are rapid, and the close correlation between IC50s in the two types of assay suggests that MTT assays could be used to evaluate cytotoxicity in neuronal cells in vitro.