Abstract
In vitro studies were carried out to substantiate the result obtained from theoretical analysis that the level of potentiation produced by joint action of insecticides could be predicted by using such parameters as the affinity of each insecticide to the degradation enzyme involved, the rate of degradation, and the I50 for target inhibition in the presence of the degradation enzyme. These parameter values were determined in a simple model system that consists only a single enzyme for degradation, carboxylesterase from the porcine liver, and the target for inhibition AChE from the electric eel. The results showed that a combination of malaoxon and paraoxon as well as malaoxon and dichlorvos among various combinations of insecticides evaluated fulfilled the conditions for potentiation satisfactorily. A comparison of I50 for AChE inhibition actually demonstrated a high level of potentiation with the above two combinations. Furthermore, the mixing ratio of two insecticides which produced the maximum potentiation level was equal to the ratio of I50 of individual insecticides. These results were in agreement with what the theoretical analysis by computer simulation suggested.
