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Lawoko G, Jarlebark L, Heilbronn E: Ligand-binding properties of an unusual nicotinic acetylcholine receptor subtype on isolated outer hair cells from guinea pig cochlea. Neurosci Lett. 1995 Jul 28;195(1):64-8.
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. |
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