In vitro effects of diisopropylfluorophosphate on cholinesterases and contractility of intact cat iris

A radiometric technique was used on intact cat irides to dissociate the effects of surface or functional cholinesterase from intracellular enzymes. This method enables the determination of the kinetics of surface enzyme activity along with simultaneous physiologic studies of iris contractile properties. The surface or external cholinesterase was found to consist of 50% acetylcholinesterase and 50% butyrylcholinesterase. Application of 3-5 μm diisopropylfluorophosphate to intact iris in vitro resulted in 60-70% inhibition of surface acetylcholinesterase associated with a 20-100-fold potentiation of mecholyl sensitivity, which was reversible by 2-pyridine aldoxime methosulfate treatment. The results indicate that it is the inhibition of the surface acetylcholinesterase of the iris which is involved in potentiation of contractility induced by agonists.