Abstract
Low level laser therapy reportedly influences soft tissue repair and nerve regeneration. The efficacy of laser therapy on soft tissues, however, remains somewhat controversial. We have made accidental findings that Ar+ laser irradiation could selectively block the generation of anode-break-excitation in frog sciatic nerve, and the effect was similar to the case of application of hyperpolarization-activated channel blockers. In the present study, we examined effects of low power laser irradiation on the contraction of gastrocnemius muscle, another excitable tissue. Twenty-six frogs (Xenopus laevis) were used. They were anesthetized by cooling and their gastrocnemius muscles with sciatic nerve were prepared. Nd:YVO4 laser (532nm, 180mW) was introduced to the surface (diameter: 6mm) of the muscle through an optical fiber (125μm). In the first experiment where electrical stimulation with supramaximal intensity to the sciatic nerve was delivered at 1/s for 12min, the laser irradiation for 3min was started at the time when the amplitude of muscle contraction decreased to 70% of maximal amplitude. It significantly (p<0.01) influenced the muscle contraction to retard its attenuation. In the second experiment where a set of stimulation and cessation was repeated three times and laser irradiation was applied during the cessation, it also influenced the successive muscle contraction to retard its attenuation (not significant). It is suggested that laser irradiation not only influences the transmission at neuromuscular junction but also has a potential to more activate the excitation-contraction coupling.
