1. High resolution EM micrograph of a skeletal muscle sarcomere (smallest contractile unit). It is the repeating unit between two Z lines. Thin filaments are the major component of the I-band and project from both sides of the Z-disc towards the center of the sarcomere. Bipolar myosin filaments extend throughout the A-band cross-linked at the centre by the M-band. Upon muscle contraction (x-bridge cycle), the A-bands do not change their length (1.6 micrometer), whereas the I-bands and the H-zone shorten.

2. Titin filaments: The sarcomere contains, in addition to thin and thick filaments, a filament system composed of the giant protein titin. Titin molecules anchor in the Z-disc and extend to the M-line of the sarcomere. Many compartments of titin in the I-band region function as a molecular spring (e.g.N2A). This spring maintains the precise structural arrangement of thick and thin filaments, and represents the passive muscle stiffness..

3. Typical immunogold-labeling protocols use primary antibodies against the epitope to be localized and commercially available gold-conjugated antibodies. Colloidal gold particles are electron dense and readily detectable in the EM. We use pre-embedding immunogold labeling on thin tissue sections, it is one of the most sensitive methods to immunolabel antigens for EM. See some selected Immuno-reactivities obtained during past years! We got many immuno-positive EM labellings with suprising and unexpected results. Contact & participate with your ABs !