title: Mitochondrial Ca2+ uptake with and without the formation of high-Ca2+ microdomains.
abstract: The mitochondrial Ca(2+) uniporter has low affinity for Ca(2+), therefore it has been assumed that submicromolar Ca(2+) signals cannot induce mitochondrial Ca(2+) uptake. The close apposition of the plasma membrane or the endoplamic reticulum (ER) to the mitochondria and the limited Ca(2+) diffusion in the cytoplasm result in the formation of perimitochondrial high-Ca(2+) microdomains (HCMDs) capable of activating mitochondrial Ca(2+) uptake. The possibility of mitochondrial Ca(2+) uptake at low submicromolar [Ca(2+)](c) has not yet been generally accepted. Earlier we found in permeabilized glomerulosa, luteal and pancreatic beta cells that [Ca(2+)](m) increased when [Ca(2+)](c) was raised from 60 nM to less than 200 nM. Here we report data obtained from H295R (adrenocortical) cells transfected with ER-targeted GFP. Cytoplasmic Ca(2+) response to angiotensin II was different in mitochondrion-rich and mitochondrion-free domains. The mitochondrial Ca(2+) response to angiotensin II correlated with GFP fluorescence indicating the vicinity of ER. When the cells were exposed to K(+) (inducing Ca(2+) influx), no correlation was found between the mitochondrial Ca(2+) signal and the vicinity of the plasma membrane or the ER. The results presented here provide evidence that mitochondrial Ca(2+) uptake may occur both with and without the formation of HCMDs within the same cell.
authors.affiliation: Department of Physiology, Faculty of Medicine, Semmelweis University and Laboratory of Cellular and Molecular Physiology, Hungarian Academy of Sciences, Budapest, Hungary.
authors.forename: Gergo
authors.initials: G
authors.lastname: Szanda
authors.forename: Péter
authors.initials: P
authors.lastname: Koncz
authors.forename: Péter
authors.initials: P
authors.lastname: Várnai
authors.forename: András
authors.initials: A
authors.lastname: Spät
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000502:physiology; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D015384:Zona Glomerulosa / Q000166:cytology / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; C034703:mitochondrial calcium uniporter; D000804:Angiotensin II; D011188:Potassium; D002118:Calcium