Spatiotemporal Imaging And Detection Of Biophotonic Activities In Retina

Biophoton is an extremely weak photon beam radiated spontaneously by the organisms in physiological or pathological conditions. The photoreceptors in retina have a large number of oxygen consumption, suggesting that the biophotonic activities of them may be extensive, but so far, no direct experimental evidence is existed for the retinal spontaneous biophoton radiation. The retinal dark noises are random small fluctuations of membrane potential in most vertebrate photoreceptors under the dark conditions, which are usually consist of two components: discrete dark noise and continuous dark noise. The retinal dark noise is the key restrictive factor of visual system sensing outside signals under the low light conditions. It is traditionally believed that the origin of the discrete dark noise is produced by the random spontaneous thermal activation of the visual pigment, while the continuous dark noise is caused by the fluctuation of the intracellular concentration of cGMP and Ca2+ in the photoreceptors. However, a large number of studies have found that the Arrhenius thermal activation energy of the rhodopsin is not enough to activate its photoisomerization. Such an energy barrier is the key problem for the original mechanism of the discrete dark noise, which has been debated for long time.In this study, by using a new developed and high-sensitive ultra-weak biophoton imaging system, we detected the biophotonic activities of rat and bullfrog retinas under the physiological conditions. Consequently, it was found that the biophoton emissions of rat and bullfrog retinas were gradually increased as the temperature increased from 34? to 36? and 38?. Such temperature-dependent effects in biophotonic activities were completely blocked either by removing intracellular and extracellular Ca2+ together or applying a phosphodiesterase 6(PDE6) inhibitor.These results suggest that there exists active biophotonic emission in retina, which may mediate physical functions of retina. In addition, our findings may provide a new thought for the explanation of origin of discrete dark noise in retina, and the possible mechanism is that the photon-like component of the discrete dark noise may be due not to directly the thermal activation of rhodopsin, but rather to an indirect thermal induction of biophotonic activities which then activate the retinal chromophore of rhodopsin.