Ca2+ hot spots on the mitochondrial surface are generated by Ca2+ mobilization from stores, but not by activation of store-operated Ca2+ channels.
Although it is widely accepted that mitochondria in living cells can efficiently uptake Ca(2+) during stimulation because of their vicinity to microdomains of high [Ca(2+)], the direct proof of Ca(2+) hot spots' existence is still lacking. Thanks to a GFP-based Ca(2+) probe localized on the cytosolic surface of the outer mitochondrial membrane, we demonstrate that, upon Ca(2+) mobilization, the [Ca(2+)] in small regions of the mitochondrial surface reaches levels 5- to 10-fold higher than in the bulk cytosol. We also show that the [Ca(2+)] to which mitochondria are exposed during capacitative Ca(2+) influx is similar between near plasma membrane mitochondria and organelles deeply located in the cytoplasm, whereas it is 2- to 3-fold higher in subplasma membrane mitochondria upon activation of voltage-gated Ca(2+) channels. These results demonstrate that mitochondria are exposed to Ca(2+) hot spots close to the ER but are excluded from the regions where capacitative Ca(2+) influx occurs.
Giacomello
Marta
M
Department of Biomedical Sciences, University of Padova, Padova, Italy.
Drago
Ilaria
I
Bortolozzi
Mario
M
Scorzeto
Michele
M
Gianelle
Alessio
A
Pizzo
Paola
P
Pozzan
Tullio
T
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002412:Cations / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D021962:Membrane Microdomains / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000473:pathology; D014162:Transfection
D015220:Calcium Channels; D002412:Cations; D049452:Green Fluorescent Proteins; D002118:Calcium