Hypoxic augmentation of Ca2+ channel currents requires a functional electron transport chain.
The incidence of Alzheimer disease is increased following ischemic episodes, and we previously demonstrated that following chronic hypoxia (CH), amyloid beta (Abeta) peptide-mediated increases in voltage-gated L-type Ca(2+) channel activity contribute to the Ca(2+) dyshomeostasis seen in Alzheimer disease. Because in certain cell types mitochondria are responsible for detecting altered O(2) levels we examined the role of mitochondrial oxidant production in the regulation of recombinant Ca(2+) channel alpha(1C) subunits during CH and exposure to Abeta-(1-40). In wild-type (rho(+)) HEK 293 cells expressing recombinant L-type alpha(1C) subunits, Ca(2+) currents were enhanced by prolonged (24 h) exposure to either CH (6% O(2)) or Abeta-(1-40) (50 nm). By contrast the response to CH was absent in rho(0) cells in which the mitochondrial electron transport chain (ETC) was depleted following long term treatment with ethidium bromide or in rho(+) cells cultured in the presence of 1 microm rotenone. CH was mimicked in rho(0) cells by the exogenous production of O2(-.). by xanthine/xanthine oxidase. Furthermore Abeta-(1-40) enhanced currents in rho(0) cells to a degree similar to that seen in cells with an intact ETC. The antioxidants ascorbate (200 microm) and Trolox (500 microm) ablated the effect of CH in rho(+) cells but were without effect on Abeta-(1-40)-mediated augmentation of Ca(2+) current in rho(0) cells. Thus oxidant production in the mitochondrial ETC is a critical factor, acting upstream of amyloid beta peptide production in the up-regulation of Ca(2+) channels in response to CH.
Brown
Stephen T
ST
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
Scragg
Jason L
JL
Boyle
John P
JP
Hudasek
Kristin
K
Peers
Chris
C
Fearon
Ian M
IM
D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000737:chemistry; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000494:pharmacology; D001692:Biological Transport; D002545:Brain Ischemia / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002460:Cell Line; D002839:Chromans / Q000494:pharmacology; D004579:Electron Transport; D004583:Electrons; D004594:Electrophysiology; D004996:Ethidium / Q000494:pharmacology; D006801:Humans; D000860:Hypoxia; D007150:Immunohistochemistry; D008928:Mitochondria / Q000378:metabolism; D019636:Neurodegenerative Diseases / Q000473:pathology; D016877:Oxidants / Q000378:metabolism / Q000494:pharmacology; D010100:Oxygen / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D017382:Reactive Oxygen Species; D012402:Rotenone / Q000494:pharmacology; D013481:Superoxides; D014162:Transfection; D015854:Up-Regulation; D014969:Xanthine Oxidase / Q000378:metabolism
D016229:Amyloid beta-Peptides; D000975:Antioxidants; D015220:Calcium Channels; D002839:Chromans; D016877:Oxidants; D010455:Peptides; D017382:Reactive Oxygen Species; D012402:Rotenone; D013481:Superoxides; D014969:Xanthine Oxidase; D004996:Ethidium; D001205:Ascorbic Acid; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D010100:Oxygen; D002118:Calcium