Diethylphosphorylation of rat cardiac M2 muscarinic receptor by chlorpyrifos oxon in vitro

The acute toxicity of chlorpyrifos oxon (CPO), the metabolically-activated form of the major organophosphorus insecticide chlorpyrifos, is attributabl e to diethylphosphorylation of acetylcholinesterase at its esteratic site. As a secondary effect, CPO is known to compete with agonist binding to the M2 muscarinic acetylcholine receptor (mAChR). This study tests the hypothes is that [ethyl-1,2-H-3]CPO labels the M2 mAChR in rat cardiac membrane ploi uins. Of four labeled protein regions observed, only one had an apparent mo lecular mass (70-75 kDa) consistent with that of glycosylated M2 mAChR. It was identified as M2 muscarinic receptor by Western blotting and immunoprec ipitation using a cardiac-specific M2 mAChR monoclonal antibody, providing the first direct evidence for diethylphosphorylation of a muscarinic recept or. This may be a functionally important M2 mAChR site, but the toxicologic al relevance and species and organ specificity of diethylphosphorylation ar e unknown. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.