title: Heteromeric TASK-1/TASK-3 is the major oxygen-sensitive background K+ channel in rat carotid body glomus cells.
abstract: Carotid body (CB) glomus cells from rat express a TASK-like background K+ channel that is believed to play a critical role in the regulation of excitability and hypoxia-induced increase in respiration. Here we studied the kinetic behaviour of single channel openings from rat CB cells to determine the molecular identity of the 'TASK-like' K+ channels. In outside-out patches, the TASK-like background K+ channel in CB cells was inhibited >90% by a reduction of pH(o) from 7.3 to 5.8. In cell-attached patches with 140 mM KCl and 1 mM Mg2+ in the bath and pipette solutions, two main open levels with conductance levels of approximately 14 pS and approximately 32 pS were recorded at a membrane potential of -60 mV. The K+ channels showed kinetic properties similar to TASK-1 (approximately 14 pS), TASK-3 (approximately 32 pS) and TASK-1/3 heteromer (approximately 32 pS). The presence of three TASK isoforms was tested by reducing [Mg2+](o) to approximately 0 mM, which had no effect on the conductance of TASK-1, but increased those of TASK-1/3 and TASK-3 to 42 pS and 74 pS, respectively. In CB cells, the reduction of [Mg2+](o) to approximately 0 mM also caused the appearance of approximately 42 pS (TASK-1/3-like) and approximately 74 pS (TASK-3-like) channels, in addition to the approximately 14 pS (TASK-1-like) channel. The 42 pS channel was the most abundant, contributing approximately 75% of the current produced by TASK-like channels. Ruthenium red (5 microM) had no effect on TASK-1 and TASK-1/3, but inhibited TASK-3 by 87%. In CB cells, ruthenium red caused approximately 12% inhibition of TASK-like activity. Methanandamide reduced the activity of all three TASKs by 80-90%, and that of TASK-like channels in CB cell also by approximately 80%. In CB cells, hypoxia caused inhibition of TASK-like channels, including TASK-1/3-like channels. These results show that TASK-1, TASK-1/3 and TASK-3 are all functionally expressed in isolated CB cells, and that the TASK-1/3 heteromer provides the major part of the oxygen-sensitive TASK-like background K+ conductance.
authors.affiliation: Department of Physiology and Biophysics, Rosalind Franklin University of Medicine and Science, The Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064, USA.
authors.forename: Donghee
authors.initials: D
authors.lastname: Kim
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Cavanaugh
authors.forename: Insook
authors.initials: I
authors.lastname: Kim
authors.forename: John L
authors.initials: JL
authors.lastname: Carroll
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D002344:Carotid Body / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D015687:Cell Hypoxia / Q000502:physiology; D004396:Coloring Agents; D004594:Electrophysiology; D006367:HeLa Cells; D006801:Humans; D007536:Isomerism; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009419:Nerve Tissue Proteins / Q000187:drug effects / Q000378:metabolism*; D010100:Oxygen / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024683:Potassium Channels, Tandem Pore Domain / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D012430:Ruthenium Red
chemical_list: D001095:Arachidonic Acids; D004396:Coloring Agents; C498655:KCNK9 protein, human; D009419:Nerve Tissue Proteins; D026902:Potassium Channel Blockers; D024683:Potassium Channels, Tandem Pore Domain; D012333:RNA, Messenger; D012430:Ruthenium Red; C088155:methanandamide; C420132:potassium channel subfamily K member 3; D008274:Magnesium; D010100:Oxygen