Abstract
Low energy visible light (LEVL) irradiation has been shown to exert some beneficial effects on various cell cultures. For example, it increases the fertilizing capability of sperm cells, promotes cell proliferation, induces sprouting of neurons, and more. To learn about the mechanism of photobiostimulation, we studied the relationship between increased intracellular calcium ([Ca2+]i) and reactive oxygen species production following LEVL illumination of cardiomyocytes. We found that visible light causes the production of O2. and H2O2 and that exogenously added H2O2 (12 microm) can mimic the effect of LEVL (3.6 J/cm2) to induce a slow and transient increase in [Ca2+]i. This [Ca2+]i elevation can be reduced by verapamil, a voltage-dependent calcium channel inhibitor. The kinetics of [Ca2+]i elevation and morphologic damage following light or addition of H2O2 were found to be dose-dependent. For example, LEVL, 3.6 J/cm2, which induced a transient increase in [Ca2+]i, did not cause any cell damage, whereas visible light at 12 J/cm2 induced a linear increase in [Ca2+]i and damaged the cells. The linear increase in [Ca2+]i resulting from high energy doses of light could be attenuated into a non-linear small rise in [Ca2+]i by the presence of extracellular catalase during illumination. We suggest that the different kinetics of [Ca2+]i elevation following various light irradiation or H2O2 treatment represents correspondingly different adaptation levels to oxidative stress. The adaptive response of the cells to LEVL represented by the transient increase in [Ca2+]i can explain LEVL beneficial effects.
Highlights
Life on earth is entirely dependent upon the interaction of sunlight with cells especially in plant photosynthesis [1]
Illuminating cardiomyocytes while scanning the Electron Paramagnetic Resonance (EPR) spectrum for 83 s resulted in the appearance of a spectrum that is compatible with that of DEPMPO-OOH (Fig. 2b), whereas the non-illuminated cell suspension spectrum exhibited only background noise (Fig. 2c)
These results show that low energy visible light (LEVL) illumination increases the level of O2. in illuminated cardiomyocytes
Summary
Life on earth is entirely dependent upon the interaction of sunlight with cells especially in plant photosynthesis [1]. Recent observations show that even low energy visible light (LEVL) can serve as a medical tool. The suggestion is based on the recent recognition that small amounts of ROS are considered to be important for mediating cell activities (16 –19). The production of ROS in response to low energy visible light has been demonstrated in fibroblasts [20], sperms [21], and lymphocytes [15]. It has been found that LEVL causes [Ca2ϩ]i elevation in cells like sperm [4] and skin [22]. A change in [Ca2ϩ]i following LEVL may be another important mediator of photobiostimulation effects. Livingston et al [29] showed that high concentrations of oxidants (Ͼ50 M) caused a sustained increase in [Ca2ϩ]i, whereas a transient increase in [Ca2ϩ]i was observed following administration of a low concentration of oxidants. More than a 4-fold increase in the [Ca2ϩ]i level was obtained in photodynamic treatment of mouse myeloma cells that had been enriched with exogenous photosensitizers before illumination, whereas only a slight increase in [Ca2ϩ]i was observed in irradiated cells without exogenous photosensitizers [30]
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