Abstract
Highly ordered lattice structure is an outstanding feature of striated muscle. It realizes condensed packing of myoproteins to a concentration unattainable with the ultracentrifugation of myoproteins. It is of interest how sarcomere stabilizes such condensed lattice structure. Skinned muscle specimen is suitable to study the intrinsic lattice stability, since it is free from the isovolumic constraint across the cell membrane. The force balance between electrostatic repulsive force and van der Waals attractive force (DLVO-theory) fails to account for the effect of low ionic strength on the lattice. The mechanical force born by sarcomeric structures such as connectin/titin and acto-myosin affinity would be significant. Actually, strong acto-myosin affinity at rigor and contracting states is considered to shrink the lattice. At resting state, the significance of acto-myosin affinity on the lattice is unclear. We prepared gelsolin treated skinned muscle specimens, from which actin filaments were successfully removed. Their lattice was observed with x-ray diffraction at BL45XU of SPring8. The results indicated that actin filament little contributes to the lattice of resting skeletal and cardiac muscles. Since lattice spacing is expected to be a significant modulator of the activation process in both muscles, reconsideration on the activation process would be necessary. [J Physiol Sci. 2007;57 Suppl:S35]
