6 research outputs found

    Mitochondrial organization and Ca2+ uptake

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    Mitochondria may function as multiple separate organelles or as a single electrically coupled continuum to modulate changes in [Ca2+]c (cytoplasmic Ca2+ concentration) in various cell types. Mitochondria may also be tethered to the internal Ca2+ store or plasma membrane in particular parts of cells to facilitate the organelles modulation of local and global [Ca2+]c increases. Differences in the organization and positioning contributes significantly to the at times apparently contradictory reports on the way mitochondria modulate [Ca2+]c signals. In the present paper, we review the organization of mitochondria and the organelles role in Ca2+ signalling

    Mitochondrial regulation of cytosolic Ca2+ signals in smooth muscle

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    The cytosolic Ca2+ concentration ([Ca2+]c) controls virtually every activity of smooth muscle, including contraction, migration, transcription, division and apoptosis. These processes may be activated by large (>10 μM) amplitude [Ca2+]c increases, which occur in small restricted regions of the cell or by smaller (<1 μM) amplitude changes throughout the bulk cytoplasm. Mitochondria contribute to the regulation of these signals by taking up Ca2+. However, mitochondria’s reported low affinity for Ca2+ is thought to require the organelle to be positioned close to ion channels and within a microdomain of high [Ca2+]. In cultured smooth muscle, mitochondria are highly dynamic structures but in native smooth muscle mitochondria are immobile, apparently strategically positioned organelles that regulate the upstroke and amplitude of IP3-evoked Ca2+ signals and IP3 receptor (IP3R) cluster activity. These observations suggest mitochondria are positioned within the high [Ca2+] microdomain arising from an IP3R cluster to exert significant local control of channel activity. On the other hand, neither the upstroke nor amplitude of voltage-dependent Ca2+ entry is modulated by mitochondria; rather, it is the declining phase of the transient that is regulated by the organelle. Control of the declining phase of the transient requires a high mitochondrial affinity for Ca2+ to enable uptake to occur over the normal physiological Ca2+ range (<1 μM). Thus, in smooth muscle, mitochondria regulate Ca2+ signals exerting effects over a large range of [Ca2+] (∼200 nM to at least tens of micromolar) to provide a wide dynamic range in the control of Ca2+ signals
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