title: The additional ACh binding site at the α4(+)/α4(-) interface of the (α4β2)2α4 nicotinic ACh receptor contributes to desensitization.
abstract: OBJECTIVE
  Nicotinic ACh (α4β2)2α4 receptors are highly prone to desensitization by prolonged exposure to low concentrations of agonist. Here, we report on the sensitivity of the three agonist sites of the (α4β2)2α4 to desensitization induced by prolonged exposure to ACh. We present electrophysiological data that show that the agonist sites of the (α4β2)2α4 receptor have different sensitivity to desensitization and that full receptor occupation decreases sensitivity to desensitization.
  
  
  METHODS
  Two-electrode voltage-clamp electrophysiology was used to study the desensitization of concatenated (α4β2)2α4 receptors expressed heterologously in Xenopus oocytes. Desensitization was assessed by measuring the degree of functional inhibition caused by prolonged exposure to ACh, as measured under equilibrium conditions. We used the single-point mutation α4W182A to measure the contribution of individual agonist sites to desensitization.
  
  
  RESULTS
  (α4β2)2α4 receptors are less sensitive to activation and desensitization by ACh than (α4β2)2β2 receptors. Incorporation of α4W182A into any of the agonist sites of concatenated (α4β2)2α4 receptors decreased sensitivity to activation and desensitization but the effects were more pronounced when the mutation was introduced into the α4(+)/α4(-) interface.
  
  
  CONCLUSIONS
  The findings suggest that the agonist sites in (α4β2)2α4 receptors are not functionally equivalent. The agonist site at the α4(+)/α4(-) interface defines the sensitivity of (α4β2)2α4 receptors to agonist-induced activation and desensitization. Functional differences between (α4β2)2α4 and (α4β2)2β2 receptors might shape the physiological and behavioural responses to nicotinic ligands when the receptors are exposed to nicotinic ligands for prolonged periods of times.
authors.affiliation: Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, UK.
authors.forename: N
authors.initials: N
authors.lastname: Benallegue
authors.forename: S
authors.initials: S
authors.lastname: Mazzaferro
authors.forename: C
authors.initials: C
authors.lastname: Alcaino
authors.forename: I
authors.initials: I
authors.lastname: Bermudez
mesh_terms: D000109:Acetylcholine / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D008024:Ligands; D018722:Nicotinic Agonists / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014982:Xenopus laevis
chemical_list: D008024:Ligands; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; C403531:nicotinic receptor alpha4beta2; D000109:Acetylcholine
keywords: concatenated receptors; high-affinity desensitization; nicotinic ACh receptors; window current; α4β2 receptors