Towards an explanation of laser-induced stimulation and damage of cell cultures

A general mechanism is proposed, capable of accounting for both the stimulating action of visible and infrared lasers on cell cultures, at low laser doses, and the damaging action at larger doses. Laser irradiation is assumed to accelerate the formation of a trans-membrane electrochemical proton gradient in mitochondria. This causes more Ca²⁺ to be released from the mitochondria to the cytoplasm by an 'antiport' process, using the proton-motive force (pmf). At low laser doses, the additional Ca²⁺ transported into the cytoplasm (among other factors controlled by the pmf) triggers mitosis and enhances cell proliferation. At higher laser doses, too much Ca²⁺ is released. This causes hyperactivity of Ca²⁺-ATPase and exhausts the ATP reserves of the cell. The nature of the photoacceptors and possible ways in which the visible and infrared laser energy is converted by the photoacceptors are discussed.