Effects of Insecticides In Vitro on Acetylcholinesterase Purified from Body Muscle of Koi Carp (Cyprinus carpio)

The inhibitory effects of various insecticides and their derivatives on acetylcholinesterase(AChE)purified from the body muscle homogenate of Koi carp(Cyprinus carpio)were examined in vitro. The p(IC50), negative logarithm of inhibitor concentration(M)required for 50% inhibition, of individual chemicals was estimated to be 3.2-8.2 and 5.4-6.1 for the organophosphates and carbamates tested, respectively. Of the 35 chemicals examined, isoxathion oxon was the most potent inhibitor as shown by p(IC50)of 8.2, and oxono organophospate compounds(with P=O)were hundreds to thousands times more inhibitory than their thiono analogues(with P=S). Azinphos, chloropyrifos, paraoxon and parathion in the form of diethyl ester were slightly more inhibitory than their dimethyl analogues, respectively. Effects of combination of different insecticides were also examined, and various combinations tested showed an additive inhibitory effect.