autoinactivation of the stargazin–ampa receptor complex subunit-dependency and independence from physical dissociationautoinactivation stargazin-ampa受体的复杂subunit-dependency和独立于物理分离.pdf

Autoinactivation of the Stargazin–AMPA Receptor Complex: Subunit-Dependency and Independence from Physical Dissociation 1 ¨ 1,2 1 2 ¨ 1 Artur Semenov , Tommi Moykkynen , Sarah K. Coleman , Esa R. Korpi , Kari Keinanen * 1 Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki, Finland, 2 Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland Abstract Agonist responses and channel kinetics of native a-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are modulated by transmembrane accessory proteins. Stargazin, the prototypical accessory protein, decreases desensitization and increases agonist potency at AMPA receptors. Furthermore, in the presence of stargazin, the steady- state responses of AMPA receptors show a gradual decline at higher glutamate concentrations. This ‘‘autoinactivation’’ has been assigned to physical dissociation of the stargazin-AMPA receptor complex and suggested to serve as a protective mechanism against overactivation. Here, we analyzed autoinactivation of GluA1–A4 AMPA receptors (all flip isoform) expressed in the presence of stargazin. Homomeric GluA1, GluA3, and GluA4 channels showed pronounced autoinactivation indicated by the bell-shaped steady-state dose response curves for glutamate. In contrast, homomeric GluA2i channels did not show significant autoinactivation. The resistance of GluA2 to autoinactivation showed striking dependence on the splice form as GluA2-flop receptors displayed clear autoinactivation. Interestingly, the resistance of GluA2-flip c