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Keywords:

  • α7;
  • bungarotoxin;
  • inactivation;
  • nicotinic;
  • receptor;
  • up-regulation

Chronic exposure to (–)nicotine has been widely reported to up-regulate nicotinic acetylcholine receptors on neurons and induce long-term inactivation as a possible cause. Nicotinic receptors containing α7 subunits are among the most abundant in brain and influence diverse cellular events. Whole-cell patch clamp recording from embryonic rat cortical neurons in culture was used to identify responses from α7-containing receptors. Immunochemical staining for glutamic acid decarboxylase (GAD) indicated that both GABAergic and non-GABAergic neurons expressed the receptors. Exposure to micromolar concentrations of nicotine for 1–4 days caused up-regulation of the receptors as measured by [α-125I]-bungarotoxin binding. Carbachol produced the same up-regulation, and cell counts demonstrated that neuronal survival was unchanged. The up-regulation was accompanied by an increased whole-cell response; no evidence was found for long-lasting inactivation. Autonomic α7-containing receptors also avoided long-lasting inactivation, even though the receptors were down-regulated by nicotine. Blocking protein synthesis or protein glycosylation prevented receptor up-regulation on cortical neurons, suggesting that new synthesis was required. No evidence was found for a pre-existing intracellular pool that supplied receptors to the surface. The results indicate that α7-containing receptors differ from other receptor subtypes in their regulation by nicotine and demonstrate further that long-lasting inactivation is not an obligatory requirement for up-regulation in this case.