Mitochondria are intracellular magnesium stores: investigation by simultaneous fluorescent imagings in PC12 cells.
To determine the nature of intracellular Mg2+ stores and Mg2+ release mechanisms in differentiated PC12 cells, Mg2+ and Ca2+ mobilizations were measured simultaneously in living cells with KMG-104, a fluorescent Mg2+ indicator, and fura-2, respectively. Treatment with the mitochondrial uncoupler, carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP), increased both the intracellular Mg2+ concentration ([Mg2+]i) and the [Ca2+]i in these cells. Possible candidates as intracellular Mg2+ stores under these conditions include intracellular divalent cation binding sites, endoplasmic reticulum (ER), Mg-ATP and mitochondria. Given that no change in [Mg2+]i was induced by caffeine application, intracellular IP3 or Ca2+ liberated by photolysis, it appears that no Mg2+ release mechanism thus exists that is mediated via the action of Ca2+ on membrane-bound receptors in the ER or via the offloading of Mg2+ from binding sites as a result of the increased [Ca2+]i. FCCP treatment for 2 min did not alter the intracellular ATP content, indicating that Mg2+ was not released from Mg-ATP, at least in the first 2 min following exposure to FCCP. FCCP-induced [Mg2+]i increase was observed at mitochondria localized area, and vice versa. These results suggest that the mitochondria serve as the intracellular Mg2+ store in PC12 cell. Simultaneous measurements of [Ca2+]i and mitochondrial membrane potential, and also of [Ca2+]i and [Mg2+]i, revealed that the initial rise in [Mg2+]i followed that of mitochondrial depolarization for several seconds. These findings show that the source of Mg2+ in the FCCP-induced [Mg2+]i increase in PC12 cells is mitochondria, and that mitochondrial depolarization triggers the Mg2+ release.
Kubota
Takeshi
T
School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa 223-8522, Japan.
Shindo
Yutaka
Y
Tokuno
Kentaro
K
Komatsu
Hirokazu
H
Ogawa
Hiroto
H
Kudo
Susumu
S
Kitamura
Yoshiichiro
Y
Suzuki
Koji
K
Oka
Kotaro
K
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002413:Cations, Divalent / Q000032:analysis / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects; D005456:Fluorescent Dyes / Q000032:analysis; D007425:Intracellular Membranes / Q000502:physiology; D007476:Ionophores / Q000494:pharmacology; D008274:Magnesium / Q000032:analysis / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D016716:PC12 Cells; D051381:Rats
D002413:Cations, Divalent; D005456:Fluorescent Dyes; D007476:Ionophores; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D002110:Caffeine; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium