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 attributable 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 hypothesis that [ethyl-1,2-(3)H]CPO labels the M2 mAChR in rat cardiac membrane proteins. Of four labeled protein regions observed, only one had an apparent molecular mass (70-75 kDa) consistent with that of glycosylated M2 mAChR. It was identified as M2 muscarinic receptor by Western blotting and immunoprecipitation using a cardiac-specific M2 mAChR monoclonal antibody, providing the first direct evidence for diethylphosphorylation of a muscarinic receptor. This may be a functionally important M2 mAChR site, but the toxicological relevance and species and organ specificity of diethylphosphorylation are unknown.
Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, 94720-3112, Berkeley, CA, USA.
J A
JA
Bomser
J E
JE
Casida
D000818:Animals; D000911:Antibodies, Monoclonal; D015153:Blotting, Western; D004390:Chlorpyrifos / Q000031:analogs & derivatives* / Q000378:metabolism / Q000633:toxicity*; D005260:Female; D007306:Insecticides / Q000378:metabolism / Q000633:toxicity*; D008565:Membrane Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D051381:Rats; D017207:Rats, Sprague-Dawley; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000276:immunology / Q000378:metabolism*; D014316:Tritium
D000911:Antibodies, Monoclonal; D007306:Insecticides; D008565:Membrane Proteins; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; D014316:Tritium; C009618:O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphate; D004390:Chlorpyrifos