title: AMP-activated protein kinase mediates carotid body excitation by hypoxia.
abstract: Early detection of an O2 deficit in the bloodstream is essential to initiate corrective changes in the breathing pattern of mammals. Carotid bodies serve an essential role in this respect; their type I cells depolarize when O2 levels fall, causing voltage-gated Ca2+ entry. Subsequent neurosecretion elicits increased afferent chemosensory fiber discharge to induce appropriate changes in respiratory function (1). Although depolarization of type I cells by hypoxia is known to arise from K+ channel inhibition, the identity of the signaling pathway has been contested, and the coupling mechanism is unknown (2). We tested the hypothesis that AMP-activated protein kinase (AMPK) is the effector of hypoxic chemotransduction. AMPK is co-localized at the plasma membrane of type I cells with O2-sensitive K+ channels. In isolated type I cells, activation of AMPK using 5-aminoimidazole-4-carboxamide riboside (AICAR) inhibited O2-sensitive K+ currents (carried by large conductance Ca2+-activated (BKCa) channels and TASK (tandem pore, acid-sensing potassium channel)-like channels, leading to plasma membrane depolarization, Ca2+ influx, and increased chemosensory fiber discharge. Conversely, the AMPK antagonist compound C reversed the effects of hypoxia and AICAR on type I cell and carotid body activation. These results suggest that AMPK activation is both sufficient and necessary for the effects of hypoxia. Furthermore, AMPK activation inhibited currents carried by recombinant BKCa channels, whereas purified AMPK phosphorylated thealpha subunit of the channel in immunoprecipitates, an effect that was stimulated by AMP and inhibited by compound C. Our findings demonstrate a central role for AMPK in stimulus-response coupling by hypoxia and identify for the first time a link between metabolic stress and ion channel regulation in an O2-sensing system.
authors.affiliation: Division of Biomedical Sciences, School of Biology, Bute Building, University of St. Andrews, St. Andrews, Fife, KY16 9TS, UK.
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Wyatt
authors.forename: Kirsty J
authors.initials: KJ
authors.lastname: Mustard
authors.forename: Selina A
authors.initials: SA
authors.lastname: Pearson
authors.forename: Mark L
authors.initials: ML
authors.lastname: Dallas
authors.forename: Lucy
authors.initials: L
authors.lastname: Atkinson
authors.forename: Prem
authors.initials: P
authors.lastname: Kumar
authors.forename: Chris
authors.initials: C
authors.lastname: Peers
authors.forename: D Grahame
authors.initials: DG
authors.lastname: Hardie
authors.forename: A Mark
authors.initials: AM
authors.lastname: Evans
mesh_terms: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D002344:Carotid Body / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004594:Electrophysiology; D006801:Humans; D000860:Hypoxia; D008564:Membrane Potentials; D009097:Multienzyme Complexes / Q000378:metabolism / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010766:Phosphorylation; D015221:Potassium Channels / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D012265:Ribonucleotides / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; D015221:Potassium Channels; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide; D010100:Oxygen; D002118:Calcium