Mutagenicity of microcystin-LR in human RSa cells.

Microcystin-LR (MCLR) is a potent cyclic heptapeptidic hepatotoxin produced by bloom-forming cyanobacteria. The mutagenicity induced by this compound in cultured human RSa cells was found by determination of ouabain-resistant (OuaR) mutation, with the highest frequency at the concentration of 15 microgram/ml. Moreover, base substitution mutations at K-ras codon 12 in genomic DNA, assessed by polymerase chain reaction (PCR) and differential dot-blot hybridization using digoxigenin-labeled probes, were detected in RSa cells 6 days after exposure to MCLR (7.5-15 microgram/ml).