science :光生物调节作用是相关激光疗法的共同机制

    美国激光医学年会的1个分组会议一直以生物刺激作用作为题目，2003年改为光生物调节作用。这方面的研究逐年上升。人们分别引入了荧光共振能量转移技 术^[[iv]]、DNA芯片技术^[[v]]和单细胞激光共焦显微镜技术^[[vi]]。近年来研究论文发表档次达到高峰，分别发表在《科学》^[[vii]]、《美国科学院院刊》^[49]、《美国生物化学杂志》^{[[viii],[ix]]}和《J Am Coll Cardio1》等^[[x]]顶级杂志上。Karu^[[xi],[xii]]，Mester等^{[[xiii],[xiv]]}和Abergel等^[[xv]]研究权威发表的5篇经典论文分别被SCI引用了118、111、110、143和101次^[[xvi]]。这些工作说明，科学界已经基本接受了光生物调节作用现象，认为光生物调节作用是相关激光疗法的共同机制，并展开了深入的机制研究。

   Extraordinary biological action of low intensity laser radiation is well known and widely used in laser therapy. In spite of a great success in this field the primary mechanism of laser stimulating effect remains disputable. The main question to be answered is: whether the observed effects are caused by absorption of light by some photoreceptors, the excitation of which starts some chains of biochemical events, or we encounter here with some other mechanism of interaction of light with biological matter. If the first is true, i.e. primary interaction of light with biological object is of pure photochemical nature, then we must find those receptors, study their properties and look for the light source, which emission is best overlapped with the absorption band of the receptors. In this case coherence and polarization of light can not be of importance.
   Indeed high coherence of light (i.e. when the phase of oscillations in electromagnetic wave remains unchanged for a long time) may be important if the phase of electron oscillations in a substance, excited by light, is also kept unchanged long enough. Large biomolecules contain tremendous number of atoms, interaction between which leads to very fast loss of the electron oscillations phase (during 10-13 sec or less). Because of this reason high coherence of light is not needed, and photochemical effects produced by coherent and noncoherent light will be indistinguishable.
   One may use a concept of spectral properties of light and substance instead of coherence and phase memory. Then the above statement can be expressed in the following form: as the spectral absorption bands of organic substances are quite broad (which means that the phase memory is short) one does not need for exciting a photochemical reaction the light with very narrow spectral line (coherent light).
   Polarization of light normally is also not important in photochemical process. It could be important if all (or majority of) absorbing molecules were oriented in space such a way that their transition moments happened to be aligned along some preferential direction. But there is absolutely no reason why the mentioned above hypothetical photoreceptors would be aligned in a body along one direction. And for random orientation of photoreceptors in a body the polarized and nonpolarized light will produce the same effect.
   So we may conclude that if the biological effect of light is based on photochemical processes (i.e. on resonance interaction of light with absorbing molecules) the coherence and polarization of light do not play any important role. From this point of view there is no special reason for using lasers in therapy instead of photodiodes or other noncoherent light sources. In case of noncoherent light source there is also no sense in using polarized light.

    Fig. demonstrates splitting of erythrocyte rouleau by the interference field of Ar-laser. Uniform illumination of an erythrocyte rouleau with a single beam of the laser does not cause any change in its structure. But as soon as the interference structure is created (by switching on the second laser beam) the rouleau is immediately split into separate red blood cells.
    There are also other experiments described in  which prove essential influence of gradient laser fields on some fundamental processes in a cell.

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