A comparative study of the uptake and photoinactivation of HeLa cells
treated with methylene blue (MB) and toluidine blue (TB) has been perf
ormed. Cell toxicity induced by different concentrations of either MB
or TB showed that 10(-5) M was the concentration at which dark damage
was not observed, while an elevated photoinactivation could be detecte
d with both thiazines. The uptake studies showed that the penetration
kinetics of 10(-5) M MB into HeLa cells is faster than that of TB, use
d at the same concentration, reaching saturation (similar to 1.8 mu g/
10(6) cells) after 6 or 12 h of incubation, respectively. For both sen
sitizers, the survival of HeLa cells was dependent on the incubation t
ime, as well as the light dose, for a given concentration (10(-5) M).
Moreover, cell photoinactivation produced by MB was higher than that p
roduced by TB. The differences between MB and TB obtained under our ex
perimental conditions are discussed.