Although laser irradiation has been reported to promote skin wound healing, the mechanism is still unclear. As mast cells are found to accumulate at the site of skin wounds we hypothesized that mast cells might be involved in the biological effects of laser irradiation. In this work the mast cells, RBL-2H3, were used in vitro to investigate the effects of laser irradiation on cellular responses. After laser irradiation, the amount of intracellular calcium ([Ca2+]i) was increased, followed by histamine release, as measured by confocal fluorescence microscopy with Fluo-3/AM staining and a fluorescence spectrometer with o-phthalaldehyde staining, respectively. The histamine release was mediated by the increment of [Ca2+]i from the influx of the extracellular buffer solution through the cation channel protein, transient receptor potential vanilloid 4 (TRPV4). The TRPV4 inhibitor, Ruthenium Red (RR) can effectively block such histamine release, indicating that TRPV4 was the key factor responding to laser irradiation. These induced responses of mast cells may provide an explanation for the biological effects of laser irradiation on promoting wound healing, as histamine is known to have multi-functions on accelerating wound healing.
In medical applications of low power laser irradiations, safety is one of the most concerning problems since the light focused by the biological object itself may cause damage of living organisms. The light distributions in an erythrocyte with the shape of native biconcave, oblate spheroid, or disk sphere under the irradiation of a plane light of 632.8 nm were studied with a numerical calculation method of finite-difference time domain. The focusing effect by either the biconcave erythrocyte, oblate spheroid, or disk sphere erythrocyte was found to be so remarkable that the light intensities at the focused areas close to the erythrocyte membrane were about 10 times higher than that of the incident light when the light irradiated along the erythrocyte plane. This focusing effect became weak and even disappeared when the irradiation direction deviated from the erythrocyte plane for more than an angle of 15 degrees. Because the highest light intensity in the erythrocyte can be about one order of magnitude higher than that of the incident light, this factor should be taken into account for laser safety in medical applications.
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