The immobilizing and lethal effect of visible radiation on mammalian and avian sperm appears to be the result of a photosensitized oxidation (photodynamic action) initiated by an endogenous intracellular pigment acting as a photonacceptor. The action spectrum of the photoimmobilization of bovine sperm reveals maxima at 440, 480, and 550 mμ. Its approximate correspondence with the absorption spectrum of these cells implicates a heme-protein, possibly one of the cytochromes as the photosensitizing agent. Excitation of this intracellular chromophore by light probably results in a triplet sensitizer-oxygen complex, free radical formation and in the induction of a primary lesion presumably in the cytoplasmic portion of the cell. Further evidence for the cytoplasmic localization of the photosensitizer was obtained from the photoinactivation of decapitate but motile and metabolically active sperm tails. Observations on the decline in the fertilizing capacity of irradiated cock sperm and on the inability of the majority of eggs fertilized with irradiated sperm to develop normally suggest that light exposure may indirectly impair the nucleic determinants in the sperm nucleus. That the photodynamic action may involve an autocatalytic reaction is inferred by the time-course of the photoreaction in terms of the decline in motility of sperm during irradiation, and by the observation that even subimmobilizing exposures of sperm to light are sufficient to eventually cause loss of motility followed by cell death, in the dark. The rate of this "dark reaction" is related to the number of quanta captured by the sensitizer. Finally, using visible light as a stressor, and spermatozoa stored in vitro as the biological test sytem, it has been possible to obtain quantitative data which establish a positive correlation between sensitivity to stress (visible radiation) and cell age. This is discussed in reference to theories of cell senescence.
ASJC Scopus subject areas
- Cell Biology