AN α-PARTICLE AUTORADIOGRAPHIC METHOD FOR QUANTIFYING THE INHIBITION OF ACETYLCHOLINESTERASE AT THE MYONEURAL JUNCTION

An existing histochemical method was adapted to α-particle autoradiography to provide a means of quantifying acetylcholinesterase inhibition at myoneural junctions. The α-particles were emitted from polonium 210 which was present in the precipitate after staining. A technique was designed for counting areas of dense α-particle tracks on the autoradiograms which corresponded to sites of acetylcholinesterase activity. An experiment was performed which showed that the track production rate was consistent for several diaphragm sections when incubated under identical conditions with no inhibitor. Tissue sections of this type, representing zero inhibition, were used as controls for inhibitor studies. It was also demonstrated that the track production rate was constant during the different exposure times used in the inhibition study. Diisopropylfluorophosphate was used to evaluate the autoradiographic method of quantifying acetylcholinesterase inhibition. A plot of log inhibitor concentration against percentage inhibition resulted in a smooth sigmoidal curve which is typical of irreversible inhibitors.