Bax affects intracellular Ca2+ stores and induces Ca2+ wave propagation

In the present study, we evaluated proapoptotic protein Bax on mitochondria and Ca2+ homeostasis in primary cultured astrocytes. We found that recombinant Bax (rBax, 10 and 100 ng/ml) induces a loss in mitochondrial membrane potential (DeltaPsi(m)). This effect might be related to the inhibition of respiratory rates and a partial release of cytochrome c, which may change mitochondrial morphology. the loss of DeltaPsi(m) and a selective permeabilization of mitochondrial membranes contribute to the release of Ca2+ from the mitochondria. This was inhibited by cyclosporin A (5 muM) and Ruthenium Red (1 mug/ml), indicating the involvement of mitochondrial Ca2+ transport mechanisms. Bax-induced mitochondrial Ca2+ release evokes Ca2+ waves and wave propagation between cells. Our results show that Bax induces mitochondrial alteration that affects Ca2+ homeostasis and signaling. These changes show that Ca2+ signals might be correlated with the proapoptotic activities of Bax.Universidade Federal de São Paulo, UNIFESP, INFAR, Dept Pharmacol, BR-04044020 São Paulo, BrazilNINDS, Biochem Sect, NIH, Bethesda, MD 20892 USAUniv São Paulo, Inst Quim, Dept Biochem, São Paulo, BrazilUniversidade Federal de São Paulo, UNIFESP, INFAR, Dept Pharmacol, BR-04044020 São Paulo, BrazilWeb of Scienc

Tissue-Specific Mitochondrial Decoding of Cytoplasmic Ca2+ Signals Is Controlled by the Stoichiometry of MICU1/2 and MCU

Mitochondrial Ca2+ uptake through the Ca2+ uniporter supports cell functions, including oxidative metabolism, while meeting tissue-specific calcium signaling patterns and energy needs. The molecular mechanisms underlying tissue-specific control of the uniporter are unknown. Here, we investigated a possible role for tissue-specific stoichiometry between the Ca2+-sensing regulators (MICUs) and pore unit (MCU) of the uniporter. Low MICU1:MCU protein ratio lowered the [Ca2+] threshold for Ca2+ uptake and activation of oxidative metabolism but decreased the cooperativity of uniporter activation in heart and skeletal muscle compared to liver. In MICU1-overexpressing cells, MICU1 was pulled down by MCU proportionally to MICU1 overexpression, suggesting that MICU1:MCU protein ratio directly reflected their association. Overexpressing MICU1 in the heart increased MICU1:MCU ratio, leading to liver-like mitochondrial Ca2+ uptake phenotype and cardiac contractile dysfunction. Thus, the proportion of MICU1-free and MICU1-associated MCU controls these tissue-specific uniporter phenotypes and downstream Ca2+ tuning of oxidative metabolism. © 201

Non-Invasive In Vivo Imaging of Calcium Signaling in Mice

Rapid and transient elevations of Ca2+ within cellular microdomains play a critical role in the regulation of many signal transduction pathways. Described here is a genetic approach for non-invasive detection of localized Ca2+ concentration ([Ca2+]) rises in live animals using bioluminescence imaging (BLI). Transgenic mice conditionally expressing the Ca2+-sensitive bioluminescent reporter GFP-aequorin targeted to the mitochondrial matrix were studied in several experimental paradigms. Rapid [Ca2+] rises inside the mitochondrial matrix could be readily detected during single-twitch muscle contractions. Whole body patterns of [Ca2+] were monitored in freely moving mice and during epileptic seizures. Furthermore, variations in mitochondrial [Ca2+] correlated to behavioral components of the sleep/wake cycle were observed during prolonged whole body recordings of newborn mice. This non-invasive imaging technique opens new avenues for the analysis of Ca2+ signaling whenever whole body information in freely moving animals is desired, in particular during behavioral and developmental studies

Subcellular and multicelluar organization of calcium signaling in liver

Cytosolic Ca2+ ([Ca2+]i) is a ubiquitous intracellular messenger in mammalian cells, and imaging studies of single living cells loaded with fluorescent Ca2+ indicators have demonstrated that the [Ca2+]i changes induced by extracellular agonists are often organized in complex temporal and spatial patterns. A number of hormones that regulate hepatic metabolism, including vasopressin and α1adrenergic agonists, bring about their effects through a rise in [Ca2+]i mediated by the Ca2+-mobilizing second messenger IP3. Imaging studies of isolated hepatocytes have demonstrated that the [Ca+]i responses during continuous exposure to these hormones consist of a series of discrete [Ca+]i spikes, the frequency of which is determined by the dose of agonist. By contrast, the amplitude and kinetics of the individual [Ca+]i spikes are not affected by changing the agonist dose. In addition to the temporal organization in the form of [Ca2+]i oscillations, the [Ca2+]i changes are also spatially organized into regenerative [Ca2+]i waves that propagate throughout the cytoplasm and nucleoplasm of the cell from a discrete plasma membrane locus. These oscillatory [Ca2+]i waves are generated by the complex interplay of [Ca2+]i and IP3 in regulating the gating properties of the IP3- receptor Ca2+ channel, which is located in the endoplasmic reticulum Ca2+ store.</jats:p