Intra- versus extracellular recovery of 16S acetylcholinesterase following organophosphate inactivation in the rat.

Acetylcholinesterase (AChE) inhibitor treatments were used to study the temporal course of intra- versus extracellular 16S AChE recovery in endplate regions of adult rat anterior gracilis muscles previously exposed to a brief, in situ application of diisopropylfluorophosphate (DFP). Following such enzymatic inactivation (95-100%), extracellular 16S AChE recovery began significantly later than that of intracellular (onset at approximately 36 and 12 h, respectively) but, once begun, progressed at approximately the same rate (1.32%/h). The recovery of AChE molecular form activities subsequent to identical DFP-inactivation was blocked to a large extent (65-85%) by in vivo treatment with cycloheximide, a protein synthesis inhibitor. These results support the hypothesis that extracellular 16S AChE at mammalian skeletal muscle motor endplates is primarily derived from complete, previously assembled 16S molecules originating in myofibers.