Increase in Intracellular Calcium Concentration Induced Differentiation of Hematopoietic Stem Cells

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Calcium (Ca2+) is a key secondary messenger. It is responsible for the generation of intracellular signals which regulates the cellular division, differentiation and cell death. Intracellular calcium concentration ([Ca2+]i) is maintained at a 105-fold lower level than the extracellular calcium concentration. The rise in [Ca2+]i induces differentiation in stem cells and this increased [Ca2+]i also serves as an early indicator of cellular death by apoptosis. In haematological malignancies such as chronic myeloid leukaemia (CML), the cells are arrested in the megakaryocytic stage and are unable to differentiate into platelets. In this study, we treated two cell lines derived from CML patients-K562 and Marimo, with Ca2+ channel blockers (CCBs) - fendiline and BTP2. We examined the effects of CCBs on cellular differentiation and growth in the two cell lines. The [Ca2+]i was found to increase with the increasing concentration of the CCBs. The morphology of the cells was then examined under a light microscope. It was observed that this increasing [Ca2+]i subsequently induced differentiation in both the cell lines. Differentiation is closely linked with proliferation. At even higher concentrations (25 µM), it was observed that these CCBs led to a decline in the number of cells. Cell cycle analysis was then performed to verify if the CCBs had an apoptotic effect on the cell lines. On performing cell cycle analysis, it was concluded that these CCBs at a higher concentration triggered apoptosis in the cells. The results suggest that CCBs causes increase in the intracellular calcium concentration in the cell lines which leads to differentiation of the hematopoietic stem cells. In addition to this, these CCBs are toxic for the cells at high concentrations as they induce apoptosis in the cell lines.