Effects of Prolonged Nicotinic Ligand Exposure on Function of Heterologously Expressed, Human α4β2- and α4β4-Nicotinic Acetylcholine Receptors

  1. Cynthia L. Gentry1,2,
  2. Lincoln H. Wilkins, Jr.1,1 and
  3. Ronald J. Lukas1,2
  1. 1Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona (C.L.G., L.H.W., R.J.L.) and 2Committee on Neuroscience, University of Arizona, Tucson, Arizona (C.L.G., R.J.L.)
  1. Ronald J. Lukas, Ph.D., Division of Neurobiology, Barrow Neurological Institute, 350 W. Thomas Rd., Phoenix, AZ 85013. E-mail: rlukas{at}chw.edu

Abstract

Effects of prolonged nicotinic ligand exposure on the function of human α4β2- and α4β4-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 α4β2-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. α4β4-nAChR was similarly sensitive to persistent inactivation by prolonged nicotine exposure. Carbamylcholine exhibited slightly lower persistent inactivation potency than nicotine at both α4β2- and α4β4-nAChR. The nAChR antagonist, mecamylamine, exhibited persistent inactivation potency and efficacy similar to nicotine at α4β2-nAChR but had a reduced effect on α4β4-nAChR. These studies illustrate persistent inactivation of human α4β2- or α4β4-nAChR induced by prolonged exposure to nicotine and show that other ligands induce nAChR persistent inactivation in a subtype-specific manner.

Footnotes

  • ↵1 Current Address: Department of Behavioral Science, College of Medicine, University of Kentucky, Lexington, KY 40546-0236.

  • This work was supported by the Ford Foundation, by scholarship support from the International Chapter, P.E.O. Sisterhood, by a grant from the Arizona Disease Control Research Commission (10011), by endowment and/or capitalization funds from the Men's and Women's Boards of the Barrow Neurological Foundation, and by the Robert and Gloria Wallace Foundation, and was conducted in part in the Charlotte and Harold Simensky Neurochemistry of Alzheimer's Disease Laboratory. Work was previously presented in preliminary form (Gentry and Lukas, 2001). The contents of this report are solely the responsibility of the authors and do not necessarily represent the views of the aforementioned awarding agencies.

  • DOI: 10.1124/jpet.102.041756

  • Abbreviations:
    nAChR
    nicotinic acetylcholine receptor
    carb
    carbamylcholine
    EBDN
    [3H]epibatidine
    mec
    mecamylamine
    ANOVA
    analysis of variance
    • Received July 16, 2002.
    • Accepted September 11, 2002.
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  1. doi: 10.1124/jpet.102.041756 JPET January 1, 2003 vol. 304 no. 1 206-216
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