title: Effects of prolonged nicotinic ligand exposure on function of heterologously expressed, human alpha4beta2- and alpha4beta4-nicotinic acetylcholine receptors.
abstract: Effects of prolonged nicotinic ligand exposure on the function of human alpha4beta2- and alpha4beta4-nicotinic acetylcholine receptor (nAChR) subtypes were studied using receptors heterologously expressed in SH-EP1 human epithelial cells. Magnitudes of acute, nAChR-mediated, specific 86Rb+ efflux responses to 1 mM carbamylcholine were reduced after pretreatment with specific nAChR ligands in effects that depended on pretreatment drug dose, duration of drug pretreatment, and duration of drug-free recovery. Fifty percent inhibition of alpha4beta2-nAChR function following 5 min of recovery occurred after 1 min of pretreatment with 1 mM nicotine but also after 1-h pretreatment at 10 nM nicotine. Seventy-five percent loss in function persisted 1 h after drug removal following 15 min or more of exposure to 1 mM nicotine. However, functional recovery was nearly complete after 1 h in drug-free medium following 1 min to 24 h pretreatment with 0.1 to 1 microM nicotine, i.e., in the range of smoker plasma nicotine levels. alpha4beta4-nAChR was similarly sensitive to persistent inactivation by prolonged nicotine exposure. Carbamylcholine exhibited slightly lower persistent inactivation potency than nicotine at both alpha4beta2- and alpha4beta4-nAChR. The nAChR antagonist, mecamylamine, exhibited persistent inactivation potency and efficacy similar to nicotine at alpha4beta2-nAChR but had a reduced effect on alpha4beta4-nAChR. These studies illustrate persistent inactivation of human alpha4beta2- or alpha4beta4-nAChR induced by prolonged exposure to nicotine and show that other ligands induce nAChR persistent inactivation in a subtype-specific manner.
authors.affiliation: Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013, USA.
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Gentry
authors.forename: Lincoln H
authors.initials: LH
authors.lastname: Wilkins
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Lukas
mesh_terms: D001667:Binding, Competitive / Q000187:drug effects; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D018678:Cholinergic Agents / Q000494:pharmacology*; D006801:Humans; D017403:In Situ Hybridization; D008024:Ligands; D008464:Mecamylamine / Q000494:pharmacology; D018721:Muscarinic Agonists / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011725:Pyridines / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism; D012414:Rubidium Radioisotopes
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D018678:Cholinergic Agents; D008024:Ligands; D018721:Muscarinic Agonists; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011725:Pyridines; D011978:Receptors, Nicotinic; D012414:Rubidium Radioisotopes; C427403:alpha(4)beta(4) nicotinic receptor; C403531:nicotinic receptor alpha4beta2; D008464:Mecamylamine; D009538:Nicotine; D002217:Carbachol; C082748:epibatidine