Muscle fiber formation in vitro is delayed by low power laser irradiation.

The myogenic cell culture provides a good in vitro model for studying the differentiation process of the muscle tissue. Although the growth of the mononucleated myoblasts is predetermined, in that they will fuse to form multinucleated muscle fibers, some control on the process of fusion can be achieved in vitro. The low power laser irradiation (LPLI) has been shown to enhance in cultured mammalian cells DNA synthesis and motility of cells. In our rat myogenic cell line (L8) system the LPLI induced a delay of 5 to 6 hours in the onset of fusion of the myoblasts compared to the nonirradiated cells. The creatine kinase activity and the incorporation of labelled thymidine of the irradiated cultures were similar to the pattern of behaviour of these parameters in the control cultures. Thus, we have extended the longevity of the myoblasts population. We assume that the delay in fusion was induced by the increase of the motility of the myoblasts in culture, so that rearrangements of physical contacts or of membrane components were needed to resume fusion.