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Figure 2. Effect of blue light on cellular succinate dehydrogenase activity correlated with population doubling time of cells. Cells were fibroblasts (Balb/c 3T3-mouse lung, HGF-human gingival, WI-38-human lung) or epithelial (MCF-7-human breast carcinoma, OSC-2-human oral squamous cell carcinoma, NHEK-normal human foreskin). Correlation (least-squares method, linear model) of population doubling time of cells vs. succinate dehydrogenase (SDH) activity (MTT method) as a percentage of no-light controls, 72 hrs after exposure to either the plasma-arc curing (A, PAC, 2 min, 60 J/cm2), quartz-tungsten halogen (B, QTH, 10 sec, 5 J/cm2), or laser (C, Laser, 30 sec, 60 J/cm2) light sources (Table). In each case (A,B, and C), the slope of the fitted line was significantly different from zero (p < 0.05). The strongest correlation between the SDH effect and doubling time was with the PAC source (C). The laser induced significant (D, 40–50%, p < 0.05, ANOVA, Tukey, n = 3) stimulation of SDH activity of WI-38 and HGF at 72 hrs and some stimulation of NHEK (30%, not significant). Error bars in D indicate standard deviations.
