Mitochondrial Ca2+ channels: Great unknowns with important functions.
ABSTRACT Mitochondria process local and global Ca(2+) signals. Thereby the spatiotemporal patterns of mitochondrial Ca(2+) signals determine whether the metabolism of these organelles is adjusted or cell death is executed. Mitochondrial Ca(2+) channels of the inner mitochondrial membrane (IMM) actually implement mitochondrial uptake from cytosolic Ca(2+) rises. Despite great efforts in the past, the identity of mitochondrial Ca(2+) channels is still elusive. Numerous studies aimed to characterize mitochondrial Ca(2+) uniport channels and provided a detailed profile of these great unknowns with important functions. This mini-review revisits previous research on the mechanisms of mitochondrial Ca(2+) uptake and aligns them with most recent findings.
Article: Spatiotemporal Correlations between Cytosolic and Mitochondrial Ca2+ Signals Using a Novel Red-Shifted Mitochondrial Targeted Cameleon[show abstract] [hide abstract]
ABSTRACT: The transfer of Ca 2+ from the cytosol into the lumen of mitochondria is a crucial process that impacts cell signaling in multiple ways. Cytosolic Ca 2+ ([Ca 2+ ] cyto) can be excellently quantified with the ratiometric Ca 2+ probe fura-2, while genetically encoded Fö rster resonance energy transfer (FRET)-based fluorescent Ca 2+ sensors, the cameleons, are efficiently used to specifically measure Ca 2+ within organelles. However, because of a significant overlap of the fura-2 emission with the spectra of the cyan and yellow fluorescent protein of most of the existing cameleons, the measurement of fura-2 and cameleons within one given cell is a complex task. In this study, we introduce a novel approach to simultaneously assess [Ca 2+ ] cyto and mitochondrial Ca 2+ ([Ca 2+ ] mito) signals at the single cell level. In order to eliminate the spectral overlap we developed a novel red-shifted cameleon, D1GO-Cam, in which the green and orange fluorescent proteins were used as the FRET pair. This ratiometric Ca 2+ probe could be successfully targeted to mitochondria and was suitable to be used simultaneously with fura-2 to correlate [Ca 2+ ] cyto and [Ca 2+ ] mito within same individual cells. Our data indicate that depending on the kinetics of [Ca 2+ ] cyto rises there is a significant lag between onset of [Ca 2+ ] cyto and [Ca 2+ ] mito signals, pointing to a certain threshold of [Ca 2+ ] cyto necessary to activate mitochondrial Ca 2+ uptake. The temporal correlation between [Ca 2+ ] mito and [Ca 2+ ] cyto as well as the efficiency of the transfer of Ca 2+ from the cytosol into mitochondria varies between different cell types. Moreover, slow mitochondrial Ca 2+ extrusion and a desensitization of mitochondrial Ca 2+ uptake cause a clear difference in patterns of mitochondrial and cytosolic Ca 2+ oscillations of pancreatic beta-cells in response to D-glucose. Copyright: ß 2012 Waldeck-Weiermair et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.PLoS ONE 09/2012; 7(9):e45917. · 4.09 Impact Factor
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ABSTRACT: Lining the inner surface of the circulatory system, the vascular endothelium accomplishes a vast variety of specialized functions. Even slight alterations of these functions are implicated in the development of certain cardiovascular diseases that represent major causes of morbidity and mortality in developed countries. Endothelial mitochondria are essential to the functional integrity of the endothelial cell as they integrate a wide range of cellular processes including Ca²⁺ handling, redox signaling and apoptosis, all of which are closely interrelated. Growing evidence supports the notion that impairment of mitochondrial signaling in the endothelium is an early event and a causative factor in the development of diseases such as atherosclerosis or diabetic complications. In this review, we want to outline the significance of mitochondria in both physiology and pathology of the vascular endothelium.Pflügers Archiv - European Journal of Physiology 03/2012; 464(1):63-76. · 4.46 Impact Factor
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ABSTRACT: The dynamin-related GTPase protein OPA1, localized in the intermembrane space and tethered to the inner membrane of mitochondria, participates in the fusion of these organelles. Its mutation is the most prevalent cause of Autosomal Dominant Optic Atrophy. OPA1 controls the diameter of the junctions between the boundary part of the inner membrane and the membrane of cristae and reduces the diffusibility of cytochrome c through these junctions. We postulated that if significant Ca²⁺ uptake into the matrix occurs from the lumen of the cristae, reduced expression of OPA1 would increase the access of Ca²⁺ to the transporters in the crista membrane and thus would enhance Ca²⁺ uptake. In intact H295R adrenocortical and HeLa cells cytosolic Ca²⁺ signals evoked with K⁺ and histamine, respectively, were transferred into the mitochondria. The rate and amplitude of mitochondrial [Ca²⁺] rise (followed with confocal laser scanning microscopy and FRET measurements with fluorescent wide-field microscopy) were increased after knockdown of OPA1, as compared with cells transfected with control RNA or mitofusin1 siRNA. Ca²⁺ uptake was enhanced despite reduced mitochondrial membrane potential. In permeabilized cells the rate of Ca²⁺ uptake by depolarized mitochondria was also increased in OPA1-silenced cells. The participation of Na⁺/Ca²⁺ and Ca²⁺/H⁺ antiporters in this transport process is indicated by pharmacological data. Altogether, our observations reveal the significance of OPA1 in the control of mitochondrial Ca²⁺ metabolism.PLoS ONE 01/2011; 6(9):e25199. · 4.09 Impact Factor