Spontaneous reactivation of organophosphorus-inhibited electroplax cholinesterase in relation to acetylcholine-induced depolarization☆

Abstract Pretreatment of the electroplax of Electrophorus electricus with irreversible inhibitors of cholinesterase (ChE) (diisopropyl phosphorofluoridate, paraoxon or phospholine) increases the sensitivity of the membrane to acetylcholine (ACh). After washing with inhibitor-free Ringer's solution, this effect disappears rapidly. Reapplication of either of the inhibitors restores the initial sensitivity to ACh. Simultaneous measurements of ChE activity show an initial inhibition which is followed by recovery of enzyme activity. The rate of reactivation of the irreversibly inhibited enzyme is highest with paraoxon and lowest with DFP. The return of enzyme activity may be responsible for the loss of ACh action on the membrane of electroplax.