Abstract
We discuss light-induced stimulation of biological activity in terms of crytosolic calcium ion concentration oscillations triggered by visible or infrared irradiation of the cells. In the visible region, endogenous or exogenous photosensitizers lead to the formation of reactive oxygen species (ROS) which stimulate the redox activity of the respiratory chain (RC). However, there is competition between photosensitization and intramolecular electronic-vibrational energy transfer from an endogenous photosensitizer to an enzyme of the RC, bringing this enzyme into an inactive configuration and thereby paralyzing the RC. Moreover, there is competition between stimulation of the redox activity of the RC by the ROS and a slower reaction of the enzymes of the RC with the ROS which again paralyzes the RC. The paralysis of the RC plays a dominant rôle in the case of ROS overproduction between reactivation of the ATPase ion pumps in the cell membranes and inhibition of the enzymes of the RC resulting from vibrational overtone excitation. Vibrational heating leading to similar effects may also be achieved by infrared laser-induced multiphoton excitation. Because of the negative influence of the competing processes, optimal irradiation conditions must be achieved to obtain photobiostimulation.
