In the current study we compare the effect of different light sources in the visible and near infra-red (IR) range on cell stimulation. It is obvious that in order to interact with the living cell, light has to be absorbed by intracellular chromophores. In a search for chromophores responsible for photobiostimulation, endogenous porphyrins, mitochondrial and membranal cytochromes were found to be suitable candidates, as they possess absorption bands in the visible and near I.R. ranges. The above-mentioned chromophores are photosensitizers that generate reactive oxygen species (ROS) following irradiation. In our opinion the first step in photobiostimulation might be ROS formation. To confirm ROS formation by various light sources, we used the electron paramagnetic resonance (EPR) associated with spin trapping techniques. All wavelengths used (360, 630, 660, 830nm), including a broad band in the visible range (400-800nm), stimulated hydroxyl radical formation in sperm cells. Measuring the amount of OH radicals as a function of the irradiating wavelength shows that shorter wavelengths might be more effective on the cell than longer ones.
2000 Japan Medical Laser Laboratory