Distinctive single-channel properties of ?4?2-nicotinic acetylcholine receptor isoforms.

ABSTRACT: Central nervous system nicotinic acetylcholine receptors (nAChR) are predominantly of the ?4?2 subtype. Two isoforms exist, with high or low agonist sensitivity (HS-(?4?2)2?2- and LS-(?4?2)2?4-nAChR). Both isoforms exhibit similar macroscopic potency and efficacy values at low acetylcholine (ACh) concentrations, mediated by a common pair of high-affinity ?4(+)/(-)?2 subunit binding interfaces. However LS-(?4?2)2?4-nAChR also respond to higher concentrations of ACh, acting at a third ?4(+)/(-)?4 subunit interface. To probe isoform functional differences further, HS- and LS-?4?2-nAChR were expressed in Xenopus laevis oocytes and single-channel responses were assessed using cell-attached patch-clamp. In the presence of a low ACh concentration, both isoforms produce low-bursting function. HS-(?4?2)2?2-nAChR exhibit a single conductance state, whereas LS-(?4?2)2?4-nAChR display two distinctive conductance states. A higher ACh concentration did not preferentially recruit either conductance state, but did result in increased LS-(?4?2)2?4-nAChR bursting and reduced closed times. Introduction of an ?4(+)/(-)?4-interface loss-of-function ?4W182A mutation abolished these changes, confirming this site's role in mediating LS-(?4?2)2?4-nAChR responses. Small or large amplitude openings are highly-correlated within individual LS-(?4?2)2?4-nAChR bursts, suggesting that they arise from distinct intermediate states, each of which is stabilized by ?4(+)/(-)?4 site ACh binding. These findings are consistent with ?4(+)/(-)?4 subunit interface occupation resulting in allosteric potentiation of agonist actions at ?4(+)/(-)?2 subunit interfaces, rather than independent induction of high conductance channel openings.

SUBMITTER: Weltzin MM 

PROVIDER: S-EPMC6405073 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature