Tags

Type your tag names separated by a space and hit enter

In vitro effects of organophosphorus anticholinesterases on muscarinic receptor-mediated inhibition of acetylcholine release in rat striatum.
Toxicol Appl Pharmacol. 2002 Jan 15; 178(2):102-8.TA

Abstract

The aim of the present study was to evaluate the in vitro modulation of muscarinic autoreceptor function by the organophosphorus (OP) anticholinesterases chlorpyrifos oxon, paraoxon, and methyl paraoxon. Acetylcholine (ACh) release was studied by preloading slices from rat striatum with [3H]choline and depolarizing with potassium (20 mM) in perfusion buffer containing hemicholinium-3 (to prevent reuptake of radiolabeled choline). Under these conditions, chlorpyrifos oxon, paraoxon, and methyl paraoxon (0.1-10 microM) all reduced ACh release in a concentration-dependent manner. Addition of the carbamate acetylcholinesterase (AChE) inhibitor physostigmine (20 microM) to the perfusion buffer also decreased ACh release. When physostigmine was present, the three oxons had no additional effect on ACh release. Concentration-dependent inhibition of AChE activity in striatal slices perfused with chlorpyrifos oxon (0.1, 1, and 10 microM) suggested AChE inhibition was responsible for oxon-mediated alterations in ACh release. To differentiate between direct and indirect actions of the OP toxicants on muscarinic autoreceptors, we compared the effects of the oxons on ACh release under two conditions, i.e., tissues were perfused with buffer containing only hemicholinium-3 or with buffer containing hemicholinium-3, physostigmine, and the nonselective muscarinic receptor blocker atropine (100 nM). In the presence of only hemicholinium-3, concentration-dependent inhibition of ACh release was again noted for all oxons, similar to the effects of the muscarinic agonists carbachol and cis-dioxolane. In the presence of physostigmine and atropine, the relative potencies of all agents were markedly reduced. Interestingly, carbachol, cis-dioxolane, paraoxon, and methyl paraoxon all decreased ACh release as before, but chlorpyrifos oxon (100-300 microM) actually increased ACh release. Together, the results suggest that chlorpyrifos oxon, paraoxon, and methyl paraoxon can activate muscarinic autoreceptors indirectly through inhibition of AChE. Both paraoxon and methyl paraoxon also directly activate whereas chlorpyrifos oxon blocks muscarinic autoreceptor function. Qualitative differences in the direct actions of these oxons at this presynaptic regulatory site could contribute to differential toxicity with high-dose exposures.

Authors+Show Affiliations

Department of Physiological Sciences, College of Veterinary Medicine, Oklahoma State University, 264 McElroy Hall, Stillwater, Oklahoma 74078, USA.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

11814330

Citation

Liu, Jing, et al. "In Vitro Effects of Organophosphorus Anticholinesterases On Muscarinic Receptor-mediated Inhibition of Acetylcholine Release in Rat Striatum." Toxicology and Applied Pharmacology, vol. 178, no. 2, 2002, pp. 102-8.
Liu J, Chakraborti T, Pope C. In vitro effects of organophosphorus anticholinesterases on muscarinic receptor-mediated inhibition of acetylcholine release in rat striatum. Toxicol Appl Pharmacol. 2002;178(2):102-8.
Liu, J., Chakraborti, T., & Pope, C. (2002). In vitro effects of organophosphorus anticholinesterases on muscarinic receptor-mediated inhibition of acetylcholine release in rat striatum. Toxicology and Applied Pharmacology, 178(2), 102-8.
Liu J, Chakraborti T, Pope C. In Vitro Effects of Organophosphorus Anticholinesterases On Muscarinic Receptor-mediated Inhibition of Acetylcholine Release in Rat Striatum. Toxicol Appl Pharmacol. 2002 Jan 15;178(2):102-8. PubMed PMID: 11814330.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - In vitro effects of organophosphorus anticholinesterases on muscarinic receptor-mediated inhibition of acetylcholine release in rat striatum. AU - Liu,Jing, AU - Chakraborti,Tamal, AU - Pope,Carey, PY - 2002/1/30/pubmed PY - 2002/3/8/medline PY - 2002/1/30/entrez SP - 102 EP - 8 JF - Toxicology and applied pharmacology JO - Toxicol Appl Pharmacol VL - 178 IS - 2 N2 - The aim of the present study was to evaluate the in vitro modulation of muscarinic autoreceptor function by the organophosphorus (OP) anticholinesterases chlorpyrifos oxon, paraoxon, and methyl paraoxon. Acetylcholine (ACh) release was studied by preloading slices from rat striatum with [3H]choline and depolarizing with potassium (20 mM) in perfusion buffer containing hemicholinium-3 (to prevent reuptake of radiolabeled choline). Under these conditions, chlorpyrifos oxon, paraoxon, and methyl paraoxon (0.1-10 microM) all reduced ACh release in a concentration-dependent manner. Addition of the carbamate acetylcholinesterase (AChE) inhibitor physostigmine (20 microM) to the perfusion buffer also decreased ACh release. When physostigmine was present, the three oxons had no additional effect on ACh release. Concentration-dependent inhibition of AChE activity in striatal slices perfused with chlorpyrifos oxon (0.1, 1, and 10 microM) suggested AChE inhibition was responsible for oxon-mediated alterations in ACh release. To differentiate between direct and indirect actions of the OP toxicants on muscarinic autoreceptors, we compared the effects of the oxons on ACh release under two conditions, i.e., tissues were perfused with buffer containing only hemicholinium-3 or with buffer containing hemicholinium-3, physostigmine, and the nonselective muscarinic receptor blocker atropine (100 nM). In the presence of only hemicholinium-3, concentration-dependent inhibition of ACh release was again noted for all oxons, similar to the effects of the muscarinic agonists carbachol and cis-dioxolane. In the presence of physostigmine and atropine, the relative potencies of all agents were markedly reduced. Interestingly, carbachol, cis-dioxolane, paraoxon, and methyl paraoxon all decreased ACh release as before, but chlorpyrifos oxon (100-300 microM) actually increased ACh release. Together, the results suggest that chlorpyrifos oxon, paraoxon, and methyl paraoxon can activate muscarinic autoreceptors indirectly through inhibition of AChE. Both paraoxon and methyl paraoxon also directly activate whereas chlorpyrifos oxon blocks muscarinic autoreceptor function. Qualitative differences in the direct actions of these oxons at this presynaptic regulatory site could contribute to differential toxicity with high-dose exposures. SN - 0041-008X UR - https://www.unboundmedicine.com/medline/citation/11814330/In_vitro_effects_of_organophosphorus_anticholinesterases_on_muscarinic_receptor_mediated_inhibition_of_acetylcholine_release_in_rat_striatum_ DB - PRIME DP - Unbound Medicine ER -