Nicotinic acetylcholine receptors containing α7 subunits on rat cortical neurons do not undergo long‐lasting inactivation even when up‐regulated by chronic nicotine exposure

Abstract

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.