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.
Bomser
J A
JA
Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, 94720-3112, Berkeley, CA, USA.
Casida
J E
JE
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