title: Extracellular calcium depletion transiently elevates oxygen consumption in neurosecretory PC12 cells through activation of mitochondrial Na+/Ca2+ exchange.
abstract: Fluctuating extracellular Ca2+ regulates many aspects of neuronal (patho)physiology including cell metabolism and respiration. Using fluorescence-based intracellular oxygen sensing technique, we demonstrate that depletion of extracellular Ca2+ from 1.8 to < or = 0.6 mM by chelation with EGTA induces a marked spike in O2 consumption in differentiated PC12 cells. This respiratory response is associated with the reduction in cytosolic and mitochondrial Ca2+, minor depolarization on the mitochondrial membrane, moderate depolarization of plasma membrane, and no changes in NAD(P)H and ATP. The response is linked to the influx of extracellular Na+ and the subsequent activation of mitochondrial Na+/Ca2+ and Na+/H+ exchange. The mitochondrial Na+/Ca2+ exchanger ((m)NCX) activated by Na+ influx reduces Ca2+ and increases Na+ levels in the mitochondrial matrix. The excess of Na+ activates the mitochondrial Na+/H+ exchanger (NHE) increasing the outward pumping of protons, electron transport and O2 consumption. Reduction in extracellular Na+ and inhibition of Na+ influx through the receptor operated calcium channels and plasmalemmal NHE reduce the respiratory response. Inhibition of the (m)NCX, L-type voltage gated Ca2+ channels or the release of Ca2+ from the endoplasmic reticulum also reduces the respiratory spike, indicating that unimpaired intercompartmental Ca2+ exchange is critical for response development.
authors.affiliation: Biochemistry Department, University College Cork, College Road, Cork, Ireland. a.zhdanov@ucc.ie
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Zhdanov
authors.forename: Manus W
authors.initials: MW
authors.lastname: Ward
authors.forename: Cormac T
authors.initials: CT
authors.lastname: Taylor
authors.forename: Ekaterina A
authors.initials: EA
authors.lastname: Souslova
authors.forename: Dmitri M
authors.initials: DM
authors.lastname: Chudakov
authors.forename: Jochen H M
authors.initials: JH
authors.lastname: Prehn
authors.forename: Dmitri B
authors.initials: DB
authors.lastname: Papkovsky
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004734:Energy Metabolism; D005110:Extracellular Space / Q000502:physiology; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism*; D010101:Oxygen Consumption; D016716:PC12 Cells; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000502:physiology*
chemical_list: D019831:Sodium-Calcium Exchanger; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002118:Calcium