[Regulatory volume increase (RVI) and apoptotic volume decrease (AVD) in U937 cells placed into hyperosmotic medium]

Time course of changes in intracellular water, K+ and Na+ of U937 cells incubated in hyperosmolar medium with addition of 200 mM sucrose was studied. Ouabain-sensitive and ouabain-resistant Rb+ (K+) influxes were measured during regulatory cell volume increase (RVI) and apoptotic volume decrease (AVD). Microscopy of cells stained by Acrydine orange, Ethydium bromide, APOPercenrage Dye and polycaspase marker FLICA was performed. We found that initial osmotic cell shrinkage induced both RVI and AVD responses. RVI dominated at the early stage whereas AVD prevailed at the later stage. In view of the data obtained in U937 cells the current opinion that RVI "dysfunction" is a prerequisite for apoptosis and AVD (Subramanyam et al., 2010) should be revised. U937 cells are capable to trigger of apoptosis and AVD in spite of the unimpaired RVI response. It is concluded that AVD plays a significant role in preventing osmotic lysis of apoptotic cells rather than in the initiation of apoptosis.