Browsing by Subject "Sarco-endoplasmic reticulum"

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    Cytoplasmic Ca2+ signals and cellular death by apoptosis in myocardiac H9c2 cells
    (2006-09) Lax Pérez, Antonio Manuel; Fernandez Belda, Francisco; Soler Pardo, Fernando; Medicina
    The incubation of H9c2 cells with 10 microM thapsigargin (TG) was associated with the appearance of a two-component cytoplasmic Ca2+ peak. Experiments performed in a Ca2+-free medium indicated that both components came from intracellular sources. The first component of the signal corresponded to the discharge of the sarco-endoplasmic reticulum (SER) Ca2+ store. The appearance of the second component was prevented by cell preincubation with cyclosporin A (CsA) and gave rise to a clear and permanent depolarization of the mitochondrial inner membrane. These features were indication of a mitochondrial origin. The observed release of mitochondrial Ca2+ was related with opening of the permeability transition pore (PTP). The two-component cytoplasmic Ca2+ peak, i.e., treatment with 10 microM TG, as compared with the first component alone, i.e., treatment with 3 microM TG, was associated with a faster process of cellular death. In both cases, chromatin fragmentation and condensation at the nuclear periphery were observed. Other prominent apoptotic events such as loss of DNA content and cleavage of poly(ADP-ribose) polymerase (PARP) were also dependent on TG concentration and occurred in different time windows. PTP opening induced by 10 microM TG was responsible for the faster apoptotic death.
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    Intracellular Ca2+ Pools and Fluxes in Cardiac Muscle-Derived H9c2 Cells
    (2005-08) Lax Pérez, Antonio Manuel; Fernandez Belda, Francisco; Soler Pardo, Fernando; Medicina
    Relevant Ca(2+) pools and fluxes in H9c2 cells have been studied using fluorescent indicators and Ca(2+)-mobilizing agents. Vasopressin produced a cytoplasmic Ca(2+) peak with half-maximal effective concentration of 6 nM, whereas thapsigargin-induced Ca(2+) increase showed half-maximal effect at 3 nM. Depolarization of the mitochondrial inner membrane by protonophore was also associated with an increase in cytoplasmic Ca(2+). Ionomycin induced a small and sustained depolarization, while thapsigargin had a small but transient effect. The thapsigargin-sensitive Ca(2+) pool was also sensitive to ionomycin, whereas the protonophore-sensitive Ca(2+) pool was not. The vasopressin-induced cytoplasmic Ca(2+) signal, which caused a reversible discharge of the sarco-endoplasmic reticulum Ca(2+) pool, was sensed as a mitochondrial Ca(2+) peak but was unaffected by the permeability transition pore inhibitor cyclosporin A. The mitochondrial Ca(2+) peak was affected by cyclosporin A when the Ca(2+) signal was induced by irreversible discharge of the intracellular Ca(2+) pool, i.e., adding thapsigargin. These observations indicate that the mitochondria interpret the cytoplasmic Ca(2+) signals generated in the reticular store.