title: Regulation of neuronal excitability by interaction of fragile X mental retardation protein with slack potassium channels.
abstract: Loss of the RNA-binding protein fragile X mental retardation protein (FMRP) represents the most common form of inherited intellectual disability. Studies with heterologous expression systems indicate that FMRP interacts directly with Slack Na(+)-activated K(+) channels (K(Na)), producing an enhancement of channel activity. We have now used Aplysia bag cell (BC) neurons, which regulate reproductive behaviors, to examine the effects of Slack and FMRP on excitability. FMRP and Slack immunoreactivity were colocalized at the periphery of isolated BC neurons, and the two proteins could be reciprocally coimmunoprecipitated. Intracellular injection of FMRP lacking its mRNA binding domain rapidly induced a biphasic outward current, with an early transient tetrodotoxin-sensitive component followed by a slowly activating sustained component. The properties of this current matched that of the native Slack potassium current, which was identified using an siRNA approach. Addition of FMRP to inside-out patches containing native Aplysia Slack channels increased channel opening and, in current-clamp recordings, produced narrowing of action potentials. Suppression of Slack expression did not alter the ability of BC neurons to undergo a characteristic prolonged discharge in response to synaptic stimulation, but prevented recovery from a prolonged inhibitory period that normally follows the discharge. Recovery from the inhibited period was also inhibited by the protein synthesis inhibitor anisomycin. Our studies indicate that, in BC neurons, Slack channels are required for prolonged changes in neuronal excitability that require new protein synthesis, and raise the possibility that channel-FMRP interactions may link changes in neuronal firing to changes in protein translation.
authors.affiliation: Department of Pharmacology, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Yalan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Maile R
authors.initials: MR
authors.lastname: Brown
authors.forename: Callen
authors.initials: C
authors.lastname: Hyland
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Jack
authors.initials: J
authors.lastname: Kronengold
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Fleming
authors.forename: Andrea B
authors.initials: AB
authors.lastname: Kohn
authors.forename: Leonid L
authors.initials: LL
authors.lastname: Moroz
authors.forename: Leonard K
authors.initials: LK
authors.lastname: Kaczmarek
mesh_terms: D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D001048:Aplysia; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D003412:Cricetulus; D055724:Electrophysiological Phenomena; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000378:metabolism*; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering; D012964:Sodium / Q000494:pharmacology; D013569:Synapses / Q000502:physiology
chemical_list: D000841:Anisomycin; D051860:Fragile X Messenger Ribonucleoprotein 1; D015221:Potassium Channels; D011500:Protein Synthesis Inhibitors; D034741:RNA, Small Interfering; D012964:Sodium