Ligand-binding properties of an unusual nicotinic acetylcholine receptor subtype on isolated outer hair cells from guinea pig cochlea.
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.
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
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