title: Mitochondrial Ca2+ uptake from plasma membrane Cav3.2 protein channels contributes to ischemic toxicity in PC12 cells.
abstract: T-type Ca(2+) channel inhibitors protect hippocampal CA1 neurons from delayed death after global ischemia in rats, suggesting that Cav3.1, Cav3.2, or Cav3.3 channels generate cytotoxic Ca(2+) elevations during anoxia. To test this hypothesis, we measured the Ca(2+) concentration changes evoked by oxygen and glucose deprivation (OGD) in the cytosol and in the mitochondria of PC12 cells. OGD evoked long-lasting cytosolic Ca(2+) elevations that were reduced by Cav3.2 inhibition (50 μm Ni(2+)) and Cav3.1/Cav3.2 silencing and potentiated by Cav3.2 overexpression. The kinetics of the sustained cytosolic Ca(2+) elevations occurring during OGD directly correlated to the extent of cell death measured 20 h after reoxygenation, which was decreased by Ni(2+) and Cav3.1/Cav3.2 silencing and increased by Cav3.2 overexpression. Ni(2+) and Cav3.1/Cav3.2 silencing delayed the decline of cellular ATP during OGD, consistent with a reduction in the Ca(2+) load actively extruded by plasma membrane Ca(2+) pumps. The cytosolic Ca(2+) elevations were paralleled by mitochondrial Ca(2+) elevations that were also increased by Cav3.2 overexpression and decreased by Ni(2+) but not by Cav3.1/Cav3.2 silencing. Overexpression and silencing of the mitochondrial Ca(2+) uniporter, the major mitochondrial Ca(2+) uptake protein, revealed that the cytotoxicity was correlated to the amplitude of the mitochondrial, rather than the cytosolic, Ca(2+) elevations. Selective activation of T-type Ca(2+) channels evoked both cytosolic and mitochondrial Ca(2+) elevations, but only the mitochondrial responses were reduced by Cav3.1/Cav3.2 silencing. We conclude that the opening of Cav3.2 channels during ischemia contribute to the entry of Ca(2+) ions that are transmitted to mitochondria, resulting in a deleterious mitochondrial Ca(2+) overload.
authors.affiliation: Department of Cell Physiology and Metabolism, University of Geneva, Geneva CH-1211, Switzerland.
authors.forename: Yves
authors.initials: Y
authors.lastname: Gouriou
authors.forename: Philippe
authors.initials: P
authors.lastname: Bijlenga
authors.forename: Nicolas
authors.initials: N
authors.lastname: Demaurex
mesh_terms: D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D051381:Rats
chemical_list: C500994:Cacna1g protein, rat; C509958:Cacna1h protein, rat; D020747:Calcium Channels, T-Type; D000255:Adenosine Triphosphate; D002118:Calcium
keywords: Calcium Signaling; Ion Channels; Ischemia; Mitochondria; Stroke