Cloning and expression of a small-conductance Ca(2+)-activated K+ channel from the mouse cochlea: coexpression with alpha9/alpha10 acetylcholine receptors.
Functional interactions between ligand-gated, voltage-, and Ca(2+)-activated ion channels are essential to the properties of excitable cells and thus to the working of the nervous system. The outer hair cells in the mammalian cochlea receive efferent inputs from the brain stem through cholinergic nerve fibers that form synapses at their base. The acetylcholine released from these efferent fibers activates fast inhibitory postsynaptic currents mediated, to some extent, by small-conductance Ca(2+)-activated K+ channels (SK) that had not been cloned. Here we report the cloning, characterization, and expression of a complete SK2 cDNA from the mouse cochlea. The cDNAs of the mouse cochlea alpha9 and alpha10 acetylcholine receptors were also obtained, sequenced, and coexpressed with the SK2 channels. Human cultured cell lines transfected with SK2 yielded Ca(2+)-sensitive K+ current that was blocked by dequalinium chloride and apamin, known blockers of SK channels. Xenopus oocytes injected with SK2 in vitro transcribed RNA, under conditions where only outward K+ currents could be recorded, expressed an outward current that was sensitive to EGTA, dequalinium chloride, and apamin. In HEK-293 cells cotransfected with cochlear SK2 plus alpha9/alpha10 receptors, acetylcholine induced an inward current followed by a robust outward current. The results indicate that SK2 and the alpha9/alpha10 acetylcholine receptors are sufficient to partly recapitulate the native hair cell efferent synaptic response.
Nie
Liping
L
Department of Otolaryngology, University of California, Davis, California 95616, USA.
Song
Haitao
H
Chen
Mei-Fang
MF
Chiamvimonvat
Nipavan
N
Beisel
Kirk W
KW
Yamoah
Ebenezer N
EN
Vázquez
Ana E
AE
D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D000891:Anti-Infective Agents, Local / Q000494:pharmacology; D001030:Apamin / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D002645:Chickens; D003001:Cloning, Molecular / Q000379:methods; D003051:Cochlea / Q000378:metabolism*; D003868:Dequalinium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D004622:Embryo, Mammalian; D004625:Embryo, Nonmammalian; D015870:Gene Expression; D006801:Humans; D007668:Kidney; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes; D018408:Patch-Clamp Techniques / Q000379:methods; D016133:Polymerase Chain Reaction / Q000379:methods; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment / Q000379:methods; D013997:Time Factors; D014162:Transfection; D014981:Xenopus
D000891:Anti-Infective Agents, Local; C498540:CHRNA9 protein, human; D002614:Chelating Agents; C470699:Chrna10 protein, rat; C402445:Chrna9 protein, mouse; C498541:Chrna9 protein, rat; D024681:Potassium Channels, Calcium-Activated; D021122:Protein Subunits; D011978:Receptors, Nicotinic; D001030:Apamin; D004533:Egtazic Acid; D003868:Dequalinium; D000109:Acetylcholine