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Hypoxia potentiates exocytosis and Ca 2+ channels in PC12 cells via increased amyloid β peptide formation and reactive oxygen species generation
Author(s) -
Green Kim N.,
Boyle John P.,
Peers Chris
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2002.017582
Subject(s) - exocytosis , reactive oxygen species , ascorbic acid , chemistry , melatonin , oxidative stress , amyloid beta , medicine , endocrinology , secretion , biochemistry , microbiology and biotechnology , biology , peptide , food science
Exposure of PC12 cells to chronic hypoxia (CH; 10 % O 2 , 24 h) augments catecholamine secretion via formation of a Cd 2+ ‐resistant Ca 2+ influx pathway, and up‐regulates native L‐type Ca 2+ channels. These effects are mimicked by exposure of cells to Alzheimer's disease‐associated amyloid β peptides (AβPs). Since pathological effects of AβPs have been associated with increased levels of reactive oxygen species (ROS), the involvement of ROS in hypoxia‐mediated up‐regulation of exocytosis and Ca 2+ channel activity was examined. Both melatonin and ascorbic acid (two structurally unrelated antioxidants) fully blocked the enhancement of catecholamine secretion caused by CH (as determined amperometrically). Enhanced immunofluorescence, observed in chronically hypoxic cells using a primary monoclonal antibody raised against the N‐terminus of AβP, was also suppressed by melatonin. Ascorbic acid, melatonin and ebselen (an additional antioxidant) also fully prevented augmentation of whole‐cell Ca 2+ currents caused by CH (as monitored using whole‐cell patch‐clamp recordings). Exposure of normoxic cells to H 2 O 2 (40 μM, 24 h), like hypoxia, caused Ca 2+ channel up‐regulation. Importantly, AβP formation appeared to be an absolute requirement for the effects of hypoxia, since the ability of CH to augment exocytosis and Ca 2+ channel activity was blocked by two novel inhibitors of γ secretase, an enzyme complex required for AβP formation. Our results indicate that the effects of hypoxia require ROS generation from AβPs, and suggest that elevated levels of ROS mediate hypoxic and AβP‐mediated pathological remodelling of Ca 2+ homeostasis.