Role of the extracellular transmembrane domain interface in gating and pharmacology of a heteromeric neuronal nicotinic receptor

Abstract

J. Neurochem. (2010) 113, 1036–1045. Abstract Nicotinic acetylcholine receptors (nAChRs) transmit the agonist signal to the channel gate through a number of extracellular domains. We have previously shown that particular details of the process of coupling binding to gating could be quantitative and qualitatively different in muscle and neuronal type nAChRs. We have extended previous studies on homomeric α7 nAChRs to heteromeric α3β4 nAChRs, by mutating residues located at loops 2 and 7, and M2–M3 linker of both α3 and β4 subunits which, in order to monitor surface expression, were modified to bind α-bungarotoxin, and expressed in Xenopus oocytes. We show that, in general, mutations in these domains of both α3 and β4 subunits affect the gating function, although the effects are slightly larger if they are inserted in the α3 subunit. However, the involvement of a previously reported intrasubunit interaction in coupling (Gln48-Ile130) seems to be restricted to the β4 subunit. We also show that mutations at these domains, particularly loop 2 of the α3 subunit, change the pharmacological profile of α3β4 nAChRs, decreasing nicotine’s and increasing cytisine’s effectiveness relative to acetylcholine. It is concluded that, unlike muscle nAChRs, the non-α subunits play a relevant role in the coupling process of neuronal α3β4 nAChRs.