Abstract: BACKGROUND ＆ AIM： Human lymphoblastoid cell line TK6 was used to investigate the in vitro genotoxicity of Microcystin-LR. MATERIAL AND METHODS： Cytotoxicity response, micronucleus(MN) and mutation frequency at tk locus induced by MCLR after 4 h or 24 h treatment were detected. RERULTS： Treatment with MCLR for 4 h did not induce a significant cytotoxic response at less than 80 μg/ml. Exposure to MCLR for 24h decreased relative survival(RS), induced both MN and TK mutation in a concentration-dependent manner. The maximum induction of MN and TK mutation were 4.8 and 5.1 times those of the control,respectively. Two distinct phenotypic colonies of TK mutants were generated , namely tk-NG and tk-SG mutant colonies but the latter dominated. CONCLUSION： MCLR was clastogenic in TK6 human lymphoblastoid cells .

Key words: Microcystin-LR, micronucleus, mutation, TK6 cell