Second harmonic generation imaging in muscle fibers

We have used second harmonic generation (SHG) imaging to quantify a strong intrinsic SHG-signal from cellular and subcellular muscle fibre preparations. In isolated single muscle cells, the intrinsic SHG-signal periodically follows the striation pattern and strongly depends on the sarcomere length and the polarization of the illuminating laser beam. At the subcellular level, the SHG signal seems to be located mainly at the overlapping region of the (thin) actin and (thick) myosin filaments. Thus, SHG imaging resolves the arrangement of the contractile structures with high resolution non-invasively and without chromophores. It may also allow to study dynamic molecular interactions of the motor protein myosin with actin filaments during force production and muscle shortening.