Abstract
It is generally accepted that the contraction of muscle fiber is reversibly inhibited by 2,3-butanedione monoxime (BDM). Since the muscle contraction takes place by the interaction between thin actin filaments and myosin heads of thick filaments, it was suggested that BDM directly inhibits the actin-myosin interaction. But detail mechanisms of the suppression of contraction by BDM are still unknown. In this study, we examined how BDM affects the transverse stiffness of myofibrils and muscle fibers by AFM. Myofibrils and muscle fibers prepared from psoas muscle of rabbit were used. The transverse stiffness was measured as in our previous studies. Modified AFM cantilevers having a glass rod attached to the tip of AFM cantilever were prepared and used for measurements to minimally alter the actin-myosin lattice structure. The tip of AFM cantilever was approached to the surface of preparations attached to coverslip, and force-curves were measured to obtain the transverse stiffness. The transverse stiffness of myofibrils decreased in the order of rigor state > contracting state > contracting state (+BDM) > relaxed state. Remarkably the transverse stiffness of myofibrils was much greater in contracting state (+BDM) than in relaxed state. For muscle fibers, the transverse stiffness decreased in the same order as above for myofibrils. These results indicate that cross-bridges are formed in contracting state (+BDM), and suggest that the suppression of muscle contraction by BDM is not simply due to the inhibition of cross-bridge formation. [J Physiol Sci. 2006;56 Suppl:S79]
