Vol. 304, Issue 1, 206-216, January 2003

Effects of Prolonged Nicotinic Ligand Exposure on Function of Heterologously Expressed, Human 42- and 44-Nicotinic Acetylcholine Receptors

Cynthia L. Gentry , Lincoln H. Wilkins, Jr.¹ and Ronald J. Lukas

Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona (C.L.G., L.H.W., R.J.L.) and Committee on Neuroscience, University of Arizona, Tucson, Arizona (C.L.G., R.J.L.)

Effects of prolonged nicotinic ligand exposure on the function of human 42- and 44-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 42-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 µM nicotine, i.e., in the range of smoker plasma nicotine levels. 44-nAChR was similarly sensitive to persistent inactivation by prolonged nicotine exposure. Carbamylcholine exhibited slightly lower persistent inactivation potency than nicotine at both 42- and 44-nAChR. The nAChR antagonist, mecamylamine, exhibited persistent inactivation potency and efficacy similar to nicotine at 42-nAChR but had a reduced effect on 44-nAChR. These studies illustrate persistent inactivation of human 42- or 44-nAChR induced by prolonged exposure to nicotine and show that other ligands induce nAChR persistent inactivation in a subtype-specific manner.