Merck

Stoichiometry for activation of neuronal α7 nicotinic receptors.

Proceedings of the National Academy of Sciences of the United States of America (2013-12-04)
Natalia Andersen, Jeremías Corradi, Steven M Sine, Cecilia Bouzat
ABSTRACT

Neuronal α7 nicotinic receptors elicit rapid cation influx in response to acetylcholine (ACh) or its hydrolysis product choline. They contribute to cognition, synaptic plasticity, and neuroprotection and have been implicated in neurodegenerative and neuropsychiatric disorders. α7, however, often localizes distal to sites of nerve-released ACh and binds ACh with low affinity, and thus elicits its biological response with low agonist occupancy. To assess the function of α7 when ACh occupies fewer than five of its identical binding sites, we measured the open-channel lifetime of individual receptors in which four of the five ACh binding sites were disabled. To improve the time resolution of the inherently brief α7 channel openings, background mutations or a potentiator was used to increase open duration. We find that, in receptors with only one intact binding site, the open-channel lifetime is indistinguishable from receptors with five intact binding sites, counter to expectations from prototypical neurotransmitter-gated ion channels where the open-channel lifetime increases with the number of binding sites occupied by agonist. Replacing the membrane-embedded domain of α7 by that of the related 5-HT3A receptor increases the number of sites that need to be occupied to achieve the maximal open-channel lifetime, thus revealing a unique interdependence between the detector and actuator domains of these receptors. The distinctive ability of a single occupancy to elicit a full biological response adapts α7 to volume transmission, a prevalent mechanism of ACh-mediated signaling in the nervous system and nonneuronal cells.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Acetylcholine iodide, ≥97%
Sigma-Aldrich
Acetylcholine bromide, ≥99%
Sigma-Aldrich
Acetylcholine perchlorate
Sigma-Aldrich
Acetylcholine chloride, ≥99% (TLC)
Sigma-Aldrich
Acetylcholine chloride, suitable for cell culture
Sigma-Aldrich
Acetylcholine chloride, pkg of 150 mg (per vial)
Sigma-Aldrich
Acetylcholine chloride, ≥99% (TLC), free-flowing, Redi-Dri