Central nervous system nicotinic acetylcholine receptors (nAChR) are predominantly of the Î±4Î²2 subtype. Two isoforms exist, with high or low agonist sensitivity (HS-(Î±4Î²2) 2 Î²2- and LS-(Î±4Î²2) 2 Î±4-nAChR). Both isoforms exhibit similar macroscopic potency and efficacy values at low acetylcholine (ACh) concentrations, mediated by a common pair of high-affinity Î±4(+)/(-)Î²2 subunit binding interfaces. However LS-(Î±4Î²2) 2 Î±4-nAChR also respond to higher concentrations of ACh, acting at a third Î±4(+)/(-)Î±4 subunit interface. To probe isoform functional differences further, HS- and LS-Î±4Î²2-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-(Î±4Î²2) 2 Î²2-nAChR exhibit a single conductance state, whereas LS-(Î±4Î²2) 2 Î±4-nAChR display two distinctive conductance states. A higher ACh concentration did not preferentially recruit either conductance state, but did result in increased LS-(Î±4Î²2) 2 Î±4-nAChR bursting and reduced closed times. Introduction of an Î±4(+)/(-)Î±4-interface loss-of-function Î±4W182A mutation abolished these changes, confirming this siteâ€™s role in mediating LS-(Î±4Î²2) 2 Î±4-nAChR responses. Small or large amplitude openings are highly-correlated within individual LS-(Î±4Î²2) 2 Î±4-nAChR bursts, suggesting that they arise from distinct intermediate states, each of which is stabilized by Î±4(+)/(-)Î±4 site ACh binding. These findings are consistent with Î±4(+)/(-)Î±4 subunit interface occupation resulting in allosteric potentiation of agonist actions at Î±4(+)/(-)Î²2 subunit interfaces, rather than independent induction of high conductance channel openings.
Digital Object Identifier (DOI)
Weltzin, Maegan M.; George, Andrew A.; Lukas, Ronald J.; and Whiteaker, Paul, "Distinctive Single-Channel Properties Of Î±4Î²2-Nicotinic Acetylcholine Receptor Isoforms" (2019). Neurobiology. 209.