Abstract
In order to determine the site of action of organophosphate group on acetylcholine (ACh) receptor surface, the effect of several antagonists of ACh has been observed with Magnus method using the isolated intestine of mice. These experiments gave following results : 1) A modified method for determining the site of action of antagonist on ACh receptor surface was established stochastically and the validity was evidenced by two trial experiments. 2) According to this justified method, the anticholinergic effect of four pairs consisting of two antagonists were demonstrated and from these results, four pairs were divided into groups acting on the same site and on the different site ; the former is two pairs consisting of pyridine aldoxime methiodide (PAM) and atropine, and parathion and isopentyl acetate, the latter is two pairs consisting of atropine and parathion, and parathion and PAM. From this fact, it was concluded that organophosphate group of parathion is attracted to, what is called, the esteratic site of ACh receptor surface in the inhibitory action against ACh. 3) From the fact that the interaction between PAM and butyl diethyl phosphate is recognized but PAM and isopropyl phosphate are independent each other in the inhibitory action against ACh, it was suggested as the possible mechanism that the butyl radical of phosphate can be to hinder the approach of PAM to the anionic site of ACh receptor surface. This is an experimental evidence that there are two active sites with the distance of 7 A on ACh receptor surface.
