Fig. 2.
AsGAR-1, an Ascaris suum homolog of the Caenorhabditis elegans G protein-linked acetylcholine receptor, GAR-1, has atypical muscarinic pharmacology. (A) AsGAR-1a is activated by 10-4 M acetylcholine (ACh), but not by a panel of other neurotransmitters. Receptor activation is expressed as a fold increase in fluorescence (RFU) over mock-transfected yeast. Octopamine (OA), dopamine (DA), tyramine (TA), histamine (HA), serotonin (5-HT), adrenaline (A) all at 10-4 M, no drug (ND). The data are the means and S.E.M. of at least three separate experiments, each with three to six replicates. (B) AsGAR-1b is activated by ACh, but not by other neurotransmitters, drugs as in A. (C) AsGAR-1 activation by a panel of muscarinic agonists: carbachol (Carb), arecoline (Arec), oxotremorine M (Oxo), bethanechol (Beth) and pilocarpine (Pilo) all at 10-4 M. (D) Antagonism of AsGAR-1 by muscarinic antagonists, expressed as a percentage of AsGAR-1 activation by ACh (10-4 M). Atropine (Atr), pirenzepine (Pir), scopolamine (Sco), promethazine (Prom), diphenhydramine (DPH), cimetidine (Cim), spiperone (Spip), mianserin (Mian) and propranolol (Prop) all 10-4 M. (E) ACh activates AsGAR-1b in a concentration-dependent manner with an EC50 of 20.3 ± 1.7 μM. ◇, no agonist and ▲, mock-transfected yeast. (F) A representative dose response curve showing the dose-dependent antagonism of ACh induced AsGAR-1b activation by promethazine. Promethazine was the most potent AsGAR-1 blocker with an IC50 of 17.6 ± 4.2 μM based on three separate experiments, each with three to six replicates.