title: Molecular mechanisms contributing to TARP regulation of channel conductance and polyamine block of calcium-permeable AMPA receptors.
abstract: Many properties of fast synaptic transmission in the brain are influenced by transmembrane AMPAR regulatory proteins (TARPs) that modulate the pharmacology and gating of AMPA-type glutamate receptors (AMPARs). Although much is known about TARP influence on AMPAR pharmacology and kinetics through their modulation of the extracellular ligand-binding domain (LBD), less is known about their regulation of the ion channel region. TARP-induced modifications in AMPAR channel behavior include increased single-channel conductance and weakened block of calcium-permeable AMPARs (CP-AMPARs) by endogenous intracellular polyamines. To investigate how TARPs modify ion flux and channel block, we examined the action of γ-2 (stargazin) on GluA1 and GluA4 CP-AMPARs. First, we compared the permeation of organic cations of different sizes. We found that γ-2 increased the permeability of several cations but not the estimated AMPAR pore size, suggesting that TARP-induced relief of polyamine block does not reflect altered pore diameter. Second, to determine whether residues in the TARP intracellular C-tail regulate polyamine block and channel conductance, we examined various γ-2 C-tail mutants. We identified the membrane proximal region of the C terminus as crucial for full TARP-attenuation of polyamine block, whereas complete deletion of the C-tail markedly enhanced the TARP-induced increase in channel conductance; thus, the TARP C-tail influences ion permeation. Third, we identified a site in the pore-lining region of the AMPAR, close to its Q/R site, that is crucial in determining the TARP-induced changes in single-channel conductance. This conserved residue represents a site of TARP action, independent of the AMPAR LBD.
authors.affiliation: Laboratory of Neurobiology, Bellvitge Biomedical Research Institute, 08907 L'Hospitalet de Llobregat, Spain, and dsoto@idibell.cat m.farrant@ucl.ac.uk s.cull-candy@ucl.ac.uk.
authors.forename: David
authors.initials: D
authors.lastname: Soto
authors.affiliation: Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom.
authors.forename: Ian D
authors.initials: ID
authors.lastname: Coombs
authors.affiliation: Laboratory of Neurobiology, Bellvitge Biomedical Research Institute, 08907 L'Hospitalet de Llobregat, Spain, and.
authors.forename: Esther
authors.initials: E
authors.lastname: Gratacòs-Batlle
authors.affiliation: Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom dsoto@idibell.cat m.farrant@ucl.ac.uk s.cull-candy@ucl.ac.uk.
authors.forename: Mark
authors.initials: M
authors.lastname: Farrant
authors.affiliation: Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, United Kingdom dsoto@idibell.cat m.farrant@ucl.ac.uk s.cull-candy@ucl.ac.uk.
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Cull-Candy
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D002460:Cell Line; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D006801:Humans; D018408:Patch-Clamp Techniques; D011073:Polyamines / Q000378:metabolism; D051381:Rats; D018091:Receptors, AMPA / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D014162:Transfection
chemical_list: C491911:Cacng2 protein, rat; D015220:Calcium Channels; D011073:Polyamines; D018091:Receptors, AMPA
keywords: AMPA receptors; TARP action; TARPs; calcium-permeable AMPARs; channel conductance; polyamine block