Motoneurons express heteromeric TWIK-related acid-sensitive K+ (TASK) channels containing TASK-1 (KCNK3) and TASK-3 (KCNK9) subunits.
Background potassium currents carried by the KCNK family of two-pore-domain K+ channels are important determinants of resting membrane potential and cellular excitability. TWIK-related acid-sensitive K+ 1 (TASK-1, KCNK3) and TASK-3 (KCNK9) are pH-sensitive subunits of the KCNK family that are closely related and coexpressed in many brain regions. There is accumulating evidence that these two subunits can form heterodimeric channels, but this evidence remains controversial. In addition, a substantial contribution of heterodimeric TASK channels to native currents has not been unequivocally established. In a heterologous expression system, we verified formation of heterodimeric TASK channels and characterized their properties; TASK-1 and TASK-3 were coimmunoprecipitated from membranes of mammalian cells transfected with the channel subunits, and a dominant negative TASK-1(Y191F) construct strongly diminished TASK-3 currents. Tandem-linked heterodimeric TASK channel constructs displayed a pH sensitivity (pK approximately 7.3) in the physiological range closer to that of TASK-1 (pK approximately 7.5) than TASK-3 (pK approximately 6.8). On the other hand, heteromeric TASK channels were like TASK-3 insofar as they were activated by high concentrations of isoflurane (0.8 mm), whereas TASK-1 channels were inhibited. The pH and isoflurane sensitivities of native TASK-like currents in hypoglossal motoneurons, which strongly express TASK-1 and TASK-3 mRNA, were best represented by TASK heterodimeric channels. Moreover, after blocking homomeric TASK-3 channels with ruthenium red, we found a major component of motoneuronal isoflurane-sensitive TASK-like current that could be attributed to heteromeric TASK channels. Together, these data indicate that TASK-1 and TASK-3 subunits coassociate in functional channels, and heteromeric TASK channels provide a substantial component of background K(+) current in motoneurons with distinct modulatory properties.
Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA.
Allison P
AP
Berg
Edmund M
EM
Talley
Jules P
JP
Manger
Douglas A
DA
Bayliss
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D019281:Dimerization; D029721:Drosophila Proteins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007002:Hypoglossal Nerve / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D007530:Isoflurane / Q000494:pharmacology; D007668:Kidney; D008969:Molecular Sequence Data; D009046:Motor Neurons / Q000378:metabolism* / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D024683:Potassium Channels, Tandem Pore Domain / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*; D055503:Protein Multimerization; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000502:physiology; D012430:Ruthenium Red / Q000494:pharmacology; D014162:Transfection
D029721:Drosophila Proteins; C498655:KCNK9 protein, human; C407082:Kcnk9 protein, rat; D009419:Nerve Tissue Proteins; C102352:Ork1 protein, Drosophila; D015221:Potassium Channels; D024683:Potassium Channels, Tandem Pore Domain; D011993:Recombinant Fusion Proteins; D012430:Ruthenium Red; C420132:potassium channel subfamily K member 3; D007530:Isoflurane; D011188:Potassium