Ion currents as initiators of light-induced effects: studies using photosensitizers

The effects of reactive oxygen species, especially as generated by photosensitizers and light, may serve as a model for light-induced effects relying on endogenous chromophores. Early events in the series of reactions initiated by these processes are reviewed and representative data on block of ionic currents, membrane permeabilization and increase in intracellular calcium concentration are presented. A general model for the effects of oxidative stress ranging from no effect with mild challenge to necrosis following severe challenge is pre - sented. The results suggest that a 1O2 mechanism could be operative for some forms of low level laser therapy. Energetic considerations suggest that this mechanism is only likely for irradiation wavelengths shorter than 1270 nm.