Effects Of Prolonged Nicotinic Ligand Exposure On Function Of Heterologously Expressed Human Î±4Î²2- And Î±4Î²4-Nicotinic Acetylcholine Receptors
Effects of prolonged nicotinic ligand exposure on the function of human Î±4Î²2- and Î±4Î²4-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 Î±4Î²2-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 Î¼M nicotine, i.e., in the range of smoker plasma nicotine levels. Î±4Î²4-nAChR was similarly sensitive to persistent inactivation by prolonged nicotine exposure. Carbamylcholine exhibited slightly lower persistent inactivation potency than nicotine at both Î±4Î²2- and Î±4Î²4-nAChR. The nAChR antagonist, mecamylamine, exhibited persistent inactivation potency and efficacy similar to nicotine at Î±4Î²2-nAChR but had a reduced effect on Î±4Î²4-nAChR. These studies illustrate persistent inactivation of human Î±4Î²2- or Î±4Î²4-nAChR induced by prolonged exposure to nicotine and show that other ligands induce nAChR persistent inactivation in a subtype-specific manner.
Journal of Pharmacology and Experimental Therapeutics
Digital Object Identifier (DOI)
Gentry, Cynthia L.; Wilkins, Lincoln H.; and Lukas, Ronald J., "Effects Of Prolonged Nicotinic Ligand Exposure On Function Of Heterologously Expressed Human Î±4Î²2- And Î±4Î²4-Nicotinic Acetylcholine Receptors" (2003). Neurobiology. 215.