Total ATP content was determined by rapidly permeabilizing 20 μl cell suspension with 80 μl dimethyl sulfoxide.
The cell suspension was diluted in 4.9 ml sterile water, and ATP content was determined in 100 μl of the preparation as described by the manufacturer. To determine the extracellular ATP concentration, the 20 μl cell suspension was mixed with 80 μl sterile water and analysed as described above. Intracellular ATP concentrations were calculated by using the intracellular volumes of 0.85 μm3. The number of cells in suspension was determined by plate spreading. The reported results are from two independent experiments.