title: Evidence for constitutively-active adenosine receptors at mammalian motor nerve endings.
abstract: A study was made to determine if constitutively active adenosine receptors are present at mouse motor nerve endings. In preparations blocked by low Ca(2+)/high Mg(2+) solution, 8-cyclopentyl-1,3,dipropylxanthine (CPX, 10-100 nM), which has been reported to be both an A(1) adenosine receptor antagonist and inverse agonist, produced a dose-dependent increase in the number of acetylcholine quanta released by a nerve impulse. Adenosine deaminase, which degrades ambient adenosine into its inactive congener, inosine, failed to alter the response to 100 nM CPX. 8-Cyclopentyltheophylline (CPT, 3 μM), a competitive inhibitor at A(1) adenosine receptors, prevented the increase in acetylcholine release produced by CPX. At normal levels of acetylcholine release, neither adenosine deaminase nor CPX affected acetylcholine release at low frequencies of nerve stimulation in (+)-tubocurarine blocked preparations. The results suggest that a proportion of the acetylcholine release process is controlled by constitutively active adenosine receptors at murine motor nerve endings, providing the first evidence for constitutive activity of G-protein-coupled receptors that modulate the function of mammalian nerve endings.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Chicago, IL 60611, USA. tjs026@northwestern.edu
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Searl
authors.forename: Eugene M
authors.initials: EM
authors.lastname: Silinsky
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D058916:Adenosine A1 Receptor Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000243:Adenosine Deaminase / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D054314:Drug Inverse Agonism; D008274:Magnesium / Q000378:metabolism; D051379:Mice; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D058915:Purinergic P1 Receptor Antagonists / Q000494:pharmacology; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology*; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology; D014970:Xanthines / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D058916:Adenosine A1 Receptor Antagonists; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D014970:Xanthines; C053907:8-cyclopentyl-1,3-dimethylxanthine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D013806:Theophylline; D000243:Adenosine Deaminase; D008274:Magnesium; D000109:Acetylcholine; D002118:Calcium