• Na+ flux;
  • Rb+ flux;
  • K+ flux;
  • Li+ flux;
  • U937 cells;
  • Apoptosis;
  • Cell ion balance;
  • Cell water balance


Unidirectional 22Na, Li+ and Rb+ fluxes and net fluxes of Na+ and K+ were measured in U937 human leukemic cells before and after induction of apoptosis by staurosporine (1 μM, 4 h) to answer the question which ion transporter(s) are responsible for changes in cell ion and water balance at apoptosis. The original version of the mathematical model of cell ion and water balance was used for analysis of the unidirectional ion fluxes under the balanced distribution of major monovalent ions across the cell membrane. The values of all major components of the Na+ and K+ efflux and influx, i.e. fluxes via the Na+,K+-ATPase pump, Na+ channels, K+ channels, Na/Na exchanger and Na-Cl symport were determined. It is concluded that apoptotic cell shrinkage and changes in Na+ and K+ fluxes typical of apoptosis in U937 cells induced by staurosporine are caused by a complex decrease in the pump activity, Na-Cl symport and integral Na+ channel permeability.