Pressure-induced changes in the connectin/titin localization in the myofibrils revealed by immunoelectron microscopy

Changes in the connectin/titin localization in post-mortem and pressurized chicken muscles were investigated by immunoelectron microscopy. The anti-connectin monoclonal antibody, 1D11, strongly labeled the sides of thick filaments near the H-zone and weakly labeled the sides of Z-line in the sarcomere prepared immediately after death. With the development of the muscle contraction, the shortening of the sarcomere and the dispersion of the connectin epitope near the H-zone were observed. With the gradual increase of the sarcomere length during further storage, the apparent increase of the width of the epitope in the A-band region stained by the antibody was observed, but the distance from the epitope to M-line remained almost the same length. In the case of high pressure treatment, significant changes in the labeling pattern of the antibody were observed with the increase of the pressure applied. The increase of the distance from the epitope to M-line and dispersion of the epitope were observed in the fiber pressurized at 100 MPa. These phenomena were accelerated with the increase of the pressure applied. The discontinuous dense materials labeled by the antibody at the thick filament near the H-zone were observed in the fiber bundles pressurized at 200 MPa or more. This is probably due to the accumulation of connectin molecule from ordinary location in the sarcomere, because of the pressure-induced destruction of the thick and connectin filaments. In the fiber bundles pressurized at 300 MPa, a significant increase in the distance from the epitope to M-line accompanied with the increase of the sarcomere length was observed. From the results obtained, it was clear that the changes in the location of the connectin epitope induced by the brief exposure to high pressure were drastic in comparison with that in the sarcomere during post-mortem storage.