title: Deactivation kinetics of acid-sensing ion channel 1a are strongly pH-sensitive.
abstract: Acid-sensing ion channels (ASICs) are trimeric cation-selective ion channels activated by protons in the physiological range. Recent reports have revealed that postsynaptically localized ASICs contribute to the excitatory postsynaptic current by responding to the transient acidification of the synaptic cleft that accompanies neurotransmission. In response to such brief acidic transients, both recombinant and native ASICs show extremely rapid deactivation in outside-out patches when jumping from a pH 5 stimulus to a single resting pH of 8. Given that the resting pH of the synaptic cleft is highly dynamic and depends on recent synaptic activity, we explored the kinetics of ASIC1a and 1a/2a heteromers to such brief pH transients over a wider [H+] range to approximate neuronal conditions better. Surprisingly, the deactivation of ASICs was steeply dependent on the pH, spanning nearly three orders of magnitude from extremely fast (<1 ms) at pH 8 to very slow (>300 ms) at pH 7. This study provides an example of a ligand-gated ion channel whose deactivation is sensitive to agonist concentrations that do not directly activate the receptor. Kinetic simulations and further mutagenesis provide evidence that ASICs show such steeply agonist-dependent deactivation because of strong cooperativity in proton binding. This capacity to signal across such a large synaptically relevant bandwidth enhances the response to small-amplitude acidifications likely to occur at the cleft and may provide ASICs with the ability to shape activity in response to the recent history of the synapse.
authors.affiliation: Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, TX 77030 david.m.macLean@uth.tmc.edu.
authors.forename: David M
authors.identifier: 0000-0001-8981-7540
authors.initials: DM
authors.lastname: MacLean
authors.affiliation: Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center, Houston, TX 77030.
authors.forename: Vasanthi
authors.initials: V
authors.lastname: Jayaraman
mesh_terms: D062565:Acid Sensing Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D002645:Chickens; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D058446:Ligand-Gated Ion Channels / Q000378:metabolism; D011522:Protons; D051381:Rats; D013569:Synapses / Q000378:metabolism; D009435:Synaptic Transmission
chemical_list: D062565:Acid Sensing Ion Channels; D058446:Ligand-Gated Ion Channels; D011522:Protons
keywords: acid-sensing ion channel; gating; kinetics; ligand-gated ion channel