Functional polymorphisms in the human β4 subunit of nicotinic acetylcholine receptors
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Human nicotinic acetylcholine receptor (nAChR) polymorphisms occur in different ethnic populations and may result in differences in nAChR ion channel properties. We have identified four nAChR beta 4 subunit (β4) nucleotide variants: 392C→T, 526C→T, 538A→G, and 1519A→G. Their corresponding amino acid substitutions are: Thr to Ile at codon 91 (T91I), Arg to Trp at codon 136 (R136W), Ser to Gly at codon 140 (S140G), and Met to Val at codon 467 (M467V), respectively. The nAChR ion channel properties of these variants were studied and compared with the more-common (wild-type) allele as wild-types. The nAChRs (α4β4 channels) were expressed heterologously in Xenopus oocytes and studied using the two-electrode voltage clamp technique to reveal functional differences between the wild-type and the variants. The receptors containing the R136W and M467V mutations (or variants) had a higher sensitivity to acetylcholine and lower EC50 than the wild-type. The T91I mutation had lower sensitivity to acetylcholine and the EC50 was larger than in wild-type nAChRs. The S140G mutation had a dose-response relationship that was similar to the wild-type. The T91I, R136W, and M467V mutations (or variants) also showed a slightly greater degree of steady-state desensitization than the wild-type in response to a 30-min exposure to one tenth of their EC50. The present results demonstrate that human β4 nAChR DNA polymorphisms result in functional changes, and suggest that certain individuals with those variants may be more or less sensitive to cholinergic drugs or to dysfunctions associated with nicotinic cholinergic systems.
KeywordsAcetylcholine Ion channel Nicotinic acetylcholine receptor Subunit Polymorphism Xenopus oocyte
We thank Dr. Laura Schrader and Dr. Hiroshi Tsuneki for technical help and the staff in Dr. David Sweatt’s laboratory for providing Xenopus oocytes. We thank Dr. Daniel Bertrand and Dr. Jon Lindstrom for providing human nAChR subunits. The work was supported by the National Institutes of Health grants from the National Institute of Neurological Disorders and Stroke and the National Institute on Drug Abuse. The experiments comply with the requirements for animal care for the Unites States and for Baylor College of Medicine.
- 3.Garcia-Guzman M, Sala F, Sala S, Campos-Caro A, Stuhmer W, Gutierrez LM, Criado M (1995) Alpha-Bungarotoxin-sensitive nicotinic receptors on bovine chromaffin cells: molecular cloning, functional expression and alternative splicing of the alpha 7 subunit. Eur J Neurosci 7:647–655PubMedGoogle Scholar
- 19.Steinlein OK, Mulley JC, Propping P, Wallace RH, Phillips HA, Sutherland GR, Scheffer IE, Berkovic SF (1995) A missense mutation in the neuronal nicotinic acetylcholine receptor alpha 4 subunit is associated with autosomal dominant nocturnal frontal lobe epilepsy. Nat Genet 11:201–203Google Scholar
- 20.Phillips HA, Favre I, Kirkpatrick M, Zuberi SM, Goudie D, Heron SE, Scheffer IE, Sutherland GR, Berkovic SF, Bertrand D, Mulley JC (2001) CHRNB2 is the second acetylcholine receptor subunit associated with autosomal dominant nocturnal frontal lobe epilepsy. Am J Hum Genet 68:225–231CrossRefPubMedGoogle Scholar
- 21.Labarca C, Schwarz J, Deshpande P, Schwarz S, Nowak MW, Fonck C, Nashmi R, Kofuji P, Dang H, Shi W, Fidan M, Khakh BS, Chen Z, Bowers BJ, Boulter J, Wehner JM, Lester HA (2001) Point mutant mice with hypersensitive alpha 4 nicotinic receptors show dopaminergic deficits and increased anxiety. Proc Natl Acad Sci U S A 98:2786–2791CrossRefPubMedGoogle Scholar
- 29.Chavez-Noriega LE, Crona JH, Washburn MS, Urrutia A, Elliott KJ, Johnson EC (1997) Pharmacological characterization of recombinant human neuronal nicotinic acetylcholine receptors h alpha 2 beta 2, h alpha 2 beta 4, h alpha 3 beta 2, h alpha 3 beta 4, h alpha 4 beta 2, h alpha 4 beta 4 and h alpha 7 expressed in Xenopus oocytes. J Pharmacol Exp Ther 280:346–356PubMedGoogle Scholar
- 35.Wada E, Wada K, Boulter J, Deneris E, Heinemann S, Patrick J, Swanson LW (1989) Distribution of alpha 2, alpha 3, alpha 4, and beta 2 neuronal nicotinic receptor subunit mRNAs in the central nervous system: a hybridization histochemical study in the rat. J Comp Neurol 284:314–335PubMedGoogle Scholar
- 41.Sachidanandam R, Weissman D, Schmidt SC, Kakol JM, Stein LD, Marth G, Sherry S, Mullikin JC, Mortimore BJ, Willey DL, Hunt SE, Cole CG, Coggill PC, Rice CM, Ning Z, Rogers J, Bentley DR, Kwok PY, Mardis ER, Yeh RT, Schultz B, Cook L, Davenport R, Dante M, Fulton L, Hillier L, Waterston RH, McPherson JD, Gilman B, Schaffner S, Van Etten WJ, Reich D, Higgins J, Daly MJ, Blumenstiel B, Baldwin J, Stange-Thomann N, Zody MC, Linton L, Lander ES, Altshuler D (2001) A map of human genome sequence variation containing 1.42 million single nucleotide polymorphisms. Nature 409:928–933CrossRefPubMedGoogle Scholar
- 42.Bertrand D, Picard F, Le Hellard S, Weiland S, Favre I, Phillips H, Bertrand S, Berkovic SF, Malafosse A, Mulley J (2002) How mutations in the nAChRs can cause ADNFLE epilepsy. Epilepsia 43 [Suppl 5]:112–122Google Scholar
- 52.Anderson C, Burns DM (2000) Patterns of adolescent smoking initiation rates by ethnicity and sex. Tob Control 9 [Suppl 2]:II4–II8Google Scholar