Some properties of glycerinated skeletal muscle fibers containing phosphorylated myosin

The structural changes of phalloidin-rhodamin labelled F-actin at relaxed and contracted skeletal muscle fibre containing phosphorylated myosin and at contracted state after dephosphorylation were investigated by measuring of polarized fluorescence of the fluorophore. The mechanical properties (isometric tension development) of fibre were studied in parallel. At submaximal concentration of Ca ions (0.6 mumol/l) the isometric tension was decreased after dephosphorylation of fibre myosin. The changes in polarization of fluorophore bound to actin filament were correlated with isometric tension developed by the muscle fibre. The angles between the actin filament long axis and the absorption and emission dipoles for contracted and relaxed fibre were different, suggesting changes in the organization of the actin monomers in thin filament, dependent on the physiological state of the fibre. The flexibility of the thin filaments during transition of the fibre from relaxed to "contracted" state increases as indicated by greater average angle between the F-actin long axis and the fibre axis.