| 15133064 |
Cuchillo-Ibanez I, Lejen T, Albillos A, Rose SD, Olivares R, Villarroya M, Garcia AG, Trifaro JM: Mitochondrial calcium sequestration and protein kinase C cooperate in the regulation of cortical F-actin disassembly and secretion in bovine chromaffin cells. J Physiol. 2004 Oct 1;560(Pt 1):63-76. Epub 2004 May 7.
Mitochondria play an important role in the homeostasis of intracellular Ca (2+) and regulate its availability for exocytosis. Inhibitors of mitochondria Ca (2+) uptake such as protonophore CCCP potentiate the secretory response to a depolarizing pulse of K (+). Exposure of cells to agents that directly (cytochalasin D, latrunculin B) or indirectly (PMA) disrupt cortical F-actin networks also potentiate the secretory response to high K (+). The effects of cytochalasin D and CCCP on secretion were additive whereas those of PMA and CCCP were not; this suggests different mechanisms for cytochalasin D and CCCP and a similar mechanism for PMA and CCCP. Mitochondria were the site of action of CCCP, because the potentiation of secretion by CCCP was observed even after depletion of Ca (2+) from the endoplasmic reticulum. CCCP induced a small increase in the cytosolic Ca (2+) concentration ([Ca (2+)](c)) that was not modified by the protein kinase C (PKC) inhibitor chelerythrine. Both CCCP and PMA induced cortical F-actin disassembly, an effect abolished by chelerythrine. In addition, rotenone and oligomycin A, two other mitochondrial inhibitors, also evoked cortical F-actin disassembly and potentiated secretion; again, these effects were blocked by chelerythrine. CCCP also enhanced the phosphorylation of PKC and myristoylated alanine-rich C kinase substance (MARCKS), and these were also inhibited by chelerythrine. The results suggest that the rapid sequestration of Ca (2+) by mitochondria would protect the cell from an enhanced PKC activation and cortical F-actin disassembly, thereby limiting the magnitude of the secretory response. |
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