[Mechanism of cell death in myeloma NS(O) in culture]

We studied in vitro myeloma cell death in a serum-free medium. Spectrophotometric assessment of DNA fragmentation, flow cytometry, and staining by Hoechst dye and ethidium bromide indicate that by the beginning of the third day cell death largely followed the apoptotic pathway. We studied dynamics of intracellular pH (pHi) during the cell death and the relationship between the pHi and apoptosis induction during cultivation in media with different pH. We have shown that decreasing pHi in the course of cell death is a consequence rather than the cause of myeloma cell death. Apoptosis took place at cultivation in the media with pH 6.3 and 8.1; the corresponding pHi values were 6.5 and 7.2, respectively. In the presence of Ca-ionophore A23187 we observed appearance of the cells with aberrant distribution of chromatin and fragmented nucleus; however calcium binding in the media with 5-10 mM EDTA induced even more pronounced nuclei fragmentation. This may indicate that both increased and decreased concentration of intracellular calcium induce NS(O) myeloma cell apoptosis.