Effect of Antibodies to Myosin Head on the Development of Rigor Tension and Stiffness in Skinned Muscle Fibers

Using three antibodies to myosin head, attaching to (1) distal region and (2) proximal region of myosin head catalytic domain, and (3) to myosin head lever arm domain, respectively, we have shown definite differences between in vitro actin-myosin sliding and muscle contraction. In the present study, we studied the effect of these antibodies on the development of rigor tension and stiffness in single skinned muscle fibers at pCa>9. To form rigor actin-myosin linkages, myosin heads should override tropomyosin, covering myosin-binding sites on actin, and to detach antibodies from them. Despite their different attachment sites in myosin head, all these antibodies slowed down development of rigor tension and stiffness with or without changing their peak values. The rigor tension versus stiffness relation was highly variable, suggesting that the rigor tension reflects the sum of tension in individual rigor linkages, while rigor stiffness represents the total number of rigor linkages. Dummy antibody had no effect on the development of rigor state. These results indicate that the action of myosin heads overriding tropomyosin is inhibited by the antibodies, so that development of rigor state is slowed down due to gradual detachment of the antibodies from individual myosin heads. Highlights The effect of three antibodies, attaching to different regions in myosin heads on the development of rigor state was examined at pCa >9, using single skinned muscle fibers. Despite their different binding sites on myosin, all the antibodies slowed down development of rigor tension and stiffness with or without changes in their peak values. The rigor tension versus stiffness relation was highly variable, suggesting that rigor tension reflects the sum of tension generated by individual myosin heads, while stiffness serves as a measure of total number of rigor linkages. These results indicate that the antibodies inhibit myosin head movement to override tropomyosin, and detachment of the antibodies from myosin heads is necessary prerequisite for rigor linkage formation.