We examined an approach in the cloning of the vast majority of those osteoblast mRNA whose transcription was highly induced when the osteoblasts were irradiated with a GaAlAs diode laser. To identify the genes induced by laser irradiation, a stepwise subtraction procedure was carried out between laser-irradiated and non-irradiated MC3T3-E1 cells. Several clones exhibited high homology with mitochondrial protein- and DNA replication related-genes. Our strategy of subtraction cloning is a powerfu1 tool for isolating the specific laser-irradiated MC3T3-E1 cells or highly induced cDNAs. This approach is useful for studying the mechanisms of cell response following bioactivation with low incident levels of laser irradiation.

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The increasing use of phototherapy (for example in wound healing) has led to a great interest in the mechanism of light-biosystem interaction. Therefore, recent observations on the enhancement of the proliferation of irradiated skin cells (fibroblasts and keratinocytes) by visible light are important to understand phototherapy at the cellular level. In the present communication we show that at the doses appropriate for enhanced fibroblast proliferation, HeNe irradiation produces transiently increasing calcium concentration in the target cells. Fibroblasts were irradiated with 1, 3 and 5 J/cm² HeNe (633 nm) laser and intracellular Ca²⁺ concentration ([Ca²⁺]i) in single cells was analyzed by Fluo-3/AM using a dynamic video imaging system with frame-grabbing software. Such observations can explain photobiostimulation because of the well-known vital rôle played by calcium in important biological processes such as proliferation and exocytosis.

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Many studies using low level laser irradiation (LLLI) have been performed to investigate the influence of laser irradiation on the healing process of wounds. It has been proposed that LLLI may stimulate the growth of bacterial cells and normal tissue cells. This study was performed to determine whether LLLI also has positive effects on the proliferation of Staphylococcus arueus, known as a common cause of skin infections, and to obtain basic data for a future in vivo experiment to study the effect of LLLI on wounds infected with S. aureus. This study includes 3 experiments: experiments for the proliferation of S. Aaureus according to (a) the LLLI pulse type, (b) the interirradiation interval and (c) the irradiation time. The experiment assessing the effect of LLLI by pulse type and energy density, pulse 13 ( P13, 6000 Hz, 14 mW of average output power) was most effective in increasing the proliferation of S. Aureus. As for the interirradiation interval (also using P13), the 4 hour interval was the most effective; 2 minutes of irradiation had a significant effect on the proliferation of S. arueus using P13 and 4 hour interval ( energy density of 14.8 mJ/cm² ).

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Over the past 15 years the author and his colleagues have treated over 1500 patients wit a wide range of pathological conditions using a variety of low power lasers (LPL) with different wavelengths and incident energy densities. The results have, however, been very good independent of these parameters. In the present study the authors offers his hypotheses as to why this should be, drawing on the physical characteristics of light and specific laser/tissue interaction models, and presents some clinical studies as examples of his experiences.

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