Neuronal Nicotinic Receptor Structure and Function

Abstract

The best characterized subtype from the branch of the neuronal nicotinic receptor (nAChR) gene family which does not bind α-bungarotoxin has the subunit stoichiometry (α4)2(β2)3 and accounts for >90% of the high affinity nicotine binding in mammalian brains. Chronic treatment of cells transfected with α4β2 AChRs causes an increase in the amount of AChR with pharmacological characteristics and a time course that parallel the nicotine-induced increase in brain α4β2 AChRs. This is the result of a decrease in turnover of surface AChRs. Many of these surface AChRs are permanently functionally inactive. The predominant subtype of the branch of the neuronal AChR gene family which binds α-bungarotoxin (α-BTX) contains α7 subunits. α7 AChRs predominate in brain, while α8 AChRs predominate in retina, and α7α8 AChRs are a minor component in both tissues. α7 and α8 homomers have similar channel properties, but α8 homomers and native α8 AChRs have lower affinity for α-BTX and higher affinity for small cholinergic ligands than do α7 homomers and α7 AChRs. The high Ca++ permeability and rapid desensitization of α7 and α8 AChRs may enable them to participate in unusual synaptic mechanisms.