Abstract
In order to study the mode of action of parathion upon acetylcholine (ACh) receptor, its inhibitory effect against ACh was examined with Magnus method using the isolated intestine of mice. These experiments gave following results : 1) From the result of a shift effect of parathion on the dose response curve of ACh, the mode of action of parathion was shown to be a competitive inhibition against ACh at doses less than 5×10-6M, but to be a non-competitive inhibition at doses greater than about 10-5M. 2) In the com petitive inhibitiory effect, the estimation of the reaction order n was not significantly different from a supposed value 1, while the n was estimated as 1.5 in the case of the non-competitive inhibition. From this fact, it was condluded that one parathion molecule antagonises one ACh molecule at ACh receptor. 3) Likewise, the reaction order n of PAM against ACh was examined by Magnus method and ACh against ChE by Warburg method, and both were estimated as 1. 4) Using parathion, PAM and atropine, the interactions between two of them to an ACh receptor were demonstrated, and all of the three pairs were shown to have relationship of additive synergism. Therefore, it was confirmed that the point of action of parathion as well as atropine is the ACh receptor.
