Orientation and length of mammalian skeletal myocytes in response to a unidirectional stretch

Effects of mechanical forces exerted on mammalian skeletal muscle cells dur ing development were studied using an in vitro model to unidirectionally st retch cultured C2C12 cells grown on silastic membrane. Previous models to d ate have not studied these responses of the mammalian system specifically. The silastic membrane upon which these cells were grown exhibited linear st rain behavior over the range of 3.6-14.6% strain, with a Poisson's ratio of approximately 0.5. To mimic murine in utero long bone growth, cell substra tes were stretched at an average strain rate of 2.36%/day for 4 days or 1.7 7%/day for 6 days with an overall membrane strain of 9.5% and 10.6%, respec tively. Both control and stretched fibers stained positively for the contra ctile protein, alpha -actinin, demonstrating muscle fiber development. An e ffect of stretch on orientation and length of myofibers was observed. At bo th strain rates, stretched fibers aligned at a smaller angle relative to th e direction of stretch and were significantly longer compared to randomly o riented control fibers. There was no effect of duration of stretch on orien tation or length, suggesting the cellular responses are independent of stra in rate for the range tested. These results demonstrate that, under conditi ons simulating mammalian long bone growth, cultured myocytes respond to mec hanical forces by lengthening and orienting along the direction of stretch.