title: Ligand-binding properties of an unusual nicotinic acetylcholine receptor subtype on isolated outer hair cells from guinea pig cochlea.
abstract: Acetylcholine receptors on isolated guinea pig cochlear outer hair cells (OHC) were characterized by radioligand binding. Equilibrium binding of [125I]alpha-bungarotoxin revealed a KD of 62 +/- 2 nM, Bmax = 7.2 +/- 1.8 x 10(7) binding sites/OHC, and a slowly reversible dissociation rate constant, kappa-1 = 2.2 +/- 0.01 x 10(-4) min-1. L-[3H]Nicotine bound reversibly (estimated KD approximately 230 nM and Bmax approximately 5 x 10(7)) with kinetic rate constants of association kappa-1 = 6.2 +/- 0.06 x 10(4) min-1 nM-1 and dissociation kappa-1 = 0.23 +/- 0.003 min-1. [3H]Strychnine bound to OHC with a KD of 35 +/- 6 nM and Bmax = 2.6 +/- 0.5 x 10(7), and binding increased 3-4 fold after membrane depolarization with 56.2 mM [K+], suggesting additional binding sites. Binding, seen only at > nM concentrations, of [3H]3-quinuclidinyl benzilate (KD = 11.5 +/- 5 nM; Bmax = 2.5 +/- 0.6 x 10(6)) was competitively inhibited by the muscarinic antagonists atropine and 4-DAMP (IC50 of 6.1 +/- 0.5 and 6.5 +/- 0.4 nM). The OHC receptor is thus an atypical nicotinic acetylcholine receptor subtype with unusual pharmacological properties.
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D002038:Bungarotoxins / Q000378:metabolism; D003051:Cochlea / Q000166:cytology / Q000378:metabolism*; D005260:Female; D006168:Guinea Pigs; D018072:Hair Cells, Auditory, Outer / Q000378:metabolism*; D066298:In Vitro Techniques; D008024:Ligands; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009538:Nicotine / Q000378:metabolism; D010276:Parasympatholytics / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011869:Radioligand Assay; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013331:Strychnine / Q000378:metabolism
chemical_list: D002038:Bungarotoxins; D008024:Ligands; D018727:Muscarinic Antagonists; D010276:Parasympatholytics; D010880:Piperidines; D011978:Receptors, Nicotinic; D011813:Quinuclidinyl Benzilate; D009538:Nicotine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D013331:Strychnine