Mitochondria respond to Ca2+ already in the submicromolar range: correlation with redox state.
Rapid formation of high-Ca2+ perimitochondrial cytoplasmic microdomains has been shown to evoke mitochondrial Ca2+ signal and activate mitochondrial dehydrogenases, however, the significance of submicromolar cytoplasmic Ca2+ concentrations in the control of mitochondrial metabolism has not been sufficiently elucidated. Here we studied the mitochondrial response to application of Ca2+ at buffered concentrations in permeabilized rat adrenal glomerulosa cells, in an insulin-producing cell line (INS-1/EK-3) and in an osteosarcoma cell line (143BmA-13). Mitochondrial Ca2+ concentration was measured with the fluorescent dye rhod-2 and, using an in situ calibration method, with the mitochondrially targeted luminescent protein mt-aequorin. In both endocrine cell types, mitochondrial Ca2+ concentration increased in response to elevated cytoplasmic Ca2+ concentration (between 60 and 740 nM) and an increase in mitochondrial Ca2+ concentration could be revealed already at a cytoplasmic Ca2+ concentration step from 60-140 nM. Similar responses were observed in the osteosarcoma cell line, although a clearcut response was first observed at 280 nM extramitochondrial Ca2+ only. As examined in glomerulosa cells, graded increases in cytoplasmic Ca2+ concentration were associated with graded increases in the reduction of mitochondrial pyridine nucleotides, consistent with Ca2+-dependent activation of mitochondrial dehydrogenases. Our data indicate that in addition to the recognized role of high-Ca2+ cytoplasmic microdomains, also small Ca2+ signals may influence mitochondrial metabolism.
Pitter
J G
JG
Department of Physiology, Semmelweis University, Faculty of Medicine, Budapest, Hungary.
Maechler
P
P
Wollheim
C B
CB
Spät
A
A
D000331:Aequorin; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002460:Cell Line; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D014407:Tumor Cells, Cultured; D015384:Zona Glomerulosa / Q000166:cytology / Q000378:metabolism
D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; C068483:rhod-2; D000331:Aequorin; D009249:NADP; D002118:Calcium