Does AMP-activated protein kinase couple inhibition of mitochondrial oxidative phosphorylation by hypoxia to calcium signaling in O2-sensing cells?
Specialized O2-sensing cells exhibit a particularly low threshold to regulation by O2 supply and function to maintain arterial pO2 within physiological limits. For example, hypoxic pulmonary vasoconstriction optimizes ventilation-perfusion matching in the lung, whereas carotid body excitation elicits corrective cardio-respiratory reflexes. It is generally accepted that relatively mild hypoxia inhibits mitochondrial oxidative phosphorylation in O2-sensing cells, thereby mediating, in part, cell activation. However, the mechanism by which this process couples to Ca2+ signaling mechanisms remains elusive, and investigation of previous hypotheses has generated contrary data and failed to unite the field. We propose that a rise in the cellular AMP/ATP ratio activates AMP-activated protein kinase and thereby evokes Ca2+ signals in O2-sensing cells. Co-immunoprecipitation identified three possible AMP-activated protein kinase subunit isoform combinations in pulmonary arterial myocytes, with alpha1 beta2 gamma1 predominant. Furthermore, their tissue-specific distribution suggested that the AMP-activated protein kinase-alpha1 catalytic isoform may contribute, via amplification of the metabolic signal, to the pulmonary selectivity required for hypoxic pulmonary vasoconstriction. Immunocytochemistry showed AMP-activated protein kinase-alpha1 to be located throughout the cytoplasm of pulmonary arterial myocytes. In contrast, it was targeted to the plasma membrane in carotid body glomus cells. Consistent with these observations and the effects of hypoxia, stimulation of AMP-activated protein kinase by phenformin or 5-aminoimidazole-4-carboxamide-riboside elicited discrete Ca2+ signaling mechanisms in each cell type, namely cyclic ADP-ribose-dependent Ca2+ mobilization from the sarcoplasmic reticulum via ryanodine receptors in pulmonary arterial myocytes and transmembrane Ca2+ influx into carotid body glomus cells. Thus, metabolic sensing by AMP-activated protein kinase may mediate chemotransduction by hypoxia.
Evans
A Mark
AM
Division of Biomedical Sciences, School of Biology, Bute Building, University of St. Andrews, St. Andrews, Fife KY16 9TS, United Kingdom. ame3@st-and.ac.uk
Mustard
Kirsteen J W
KJ
Wyatt
Christopher N
CN
Peers
Chris
C
Dipp
Michelle
M
Kumar
Prem
P
Kinnear
Nicholas P
NP
Hardie
D Grahame
DG
D055372:AMP-Activated Protein Kinases; D000244:Adenosine Diphosphate / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D000906:Antibodies / Q000737:chemistry; D002118:Calcium / Q000378:metabolism*; D002339:Carotid Arteries / Q000473:pathology; D002384:Catalysis; D004305:Dose-Response Relationship, Drug; D000860:Hypoxia; D007150:Immunohistochemistry; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000378:metabolism / Q000502:physiology*; D032389:Myocytes, Smooth Muscle / Q000166:cytology; D010085:Oxidative Phosphorylation; D010100:Oxygen / Q000378:metabolism*; D010766:Phosphorylation; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D011651:Pulmonary Artery / Q000166:cytology; D051381:Rats; D017208:Rats, Wistar; D012266:Ribose / Q000737:chemistry; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D015398:Signal Transduction; D013050:Spectrometry, Fluorescence
D000906:Antibodies; D009097:Multienzyme Complexes; D020033:Protein Isoforms; D012433:Ryanodine; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D012266:Ribose; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D010100:Oxygen; D002118:Calcium