Routes of Ca2+ Shuttling during Ca2+ Oscillations; Focus on the Role of Mitochondrial Ca2+ Handling and Cytosolic Ca2+ Buffers [Computational Biology]
September 22nd, 2015 by Pecze, L., Blum, W., Schwaller, B.
In some cell types, Ca2+ oscillations are strictly dependent on Ca2+ influx across the plasma membrane, while in others oscillations also persist in the absence of Ca2+ influx. We observed that in primary mesothelial cells, the plasmalemmal Ca2+ influx played a pivotal role. However, when the Ca2+ transport across the plasma membrane by the "lanthanum insulation method" was blocked prior to the induction of the serum-induced Ca2+ oscillations, mitochondrial Ca2+ transport was found to be able to substitute for the plasmalemmal Ca2+ exchange function, thus rendering the oscillations independent of extracellular Ca2+. However, in a physiological situation, the Ca2+-buffering capacity of mitochondria was found not to be essential for Ca2+ oscillations. Moreover, brief spontaneous Ca2+ changes were observed in the mitochondrial Ca2+ concentration without apparent changes in the cytosolic Ca2+ concentration indicating the presence of a mitochondrial autonomous Ca2+ signaling mechanism. In the presence of calretinin, a Ca2+-buffering protein, the amplitude of cytosolic spikes during oscillations was decreased and the amount of Ca2+ ions taken up by mitochondria was reduced. Thus, the increased calretinin expression observed in mesothelioma cells and in certain colon cancer might be correlated to the increased resistance of these tumor cells to pro-apoptotic/pro-necrotic signals. We identified and characterized (experimentally and by modeling) three Ca2+ shuttling pathways in primary mesothelial cells during Ca2+ oscillations: Ca2+ shuttled between I) the ER and mitochondria II) the ER and the extracellular space and III) the ER and cytoplasmic Ca2+ buffers.