In vitro effects of chlorpyrifos on the acetylcholinesterase activity of euryhaline fish, Oreochromis mossambicus.

The in vitro effect of a widely used organophosphorus insecticide, chlorpyrifos (CPP), on the acetylcholinesterase (AChE) activity was studied in vitro. The kinetic constants Km and Vmax and the bimolecular constant k(j) were determined in vitro. The in vitro AChE study indicated that CPP is neurotoxic and that it alters the apparent Km values widely in a concentration-dependent manner, resulting in a competitive type of inhibition. Based on the k(i) values, the sensitivity of AChE in brain is greater than that in gill tissue, at 7.3 x 10(-5) M and 11.92 x 10(-5) M, respectively. The study points to the importance of kinetic studies and the results suggest that in biomonitoring programmes brain AChE activity can be a good diagnostic tool for CPP toxicity.