Lattice arrangement of myosin filaments correlates with fiber type in rat skeletal muscle

Figure 1.. Simple and superlattice models. (A) Simple (left) and superlattice (right) models of transverse sections of thick filament bare regions in electron micrographs. (B) Sampling of intensity on myosin layer lines of x-ray diffraction pattern. 10, 11, etc. show positions of reflections on equator. 43.0, 21.5, and 14.3 nm show positions of first, second, and third myosin layer lines. In the simple lattice, note alignment of layer line sampled spots with corresponding equatorial reflections; in the case of the superlattice, the sampling is more complex. Based on Luther et al. (1996) and Harford and Squire (1986), with permission.

Figure 2.. X-ray diffraction patterns of rat SOL (A) and EDL (B) intact muscles. ML1-6 indicate positions of myosin layer lines (repeat 43 nm), and ALL indicates the position of the 5.9-nm actin layer line. Horizontal inserts on equator show shorter exposures to reveal the high-intensity equatorial 1,0 and 1,1 and Z-line reflections. Prominent lattice sampling is seen in SOL at the same positions as equatorial reflections (vertical rectangles aligning with 1,0 and 1,1 reflections). This indicates a simple lattice of myosin filaments. Lattice sampling is largely absent in EDL, except for weak superlattice spot circled. The pattern suggests a local superlattice with disorder. Scale at left is intensity in arbitrary units (upper, equator; lower, rest of pattern).

Figure 3.. Transverse sections of bare region of rat SOL and EDL revealing lattice type. (A) SOL shows triangular filament profiles pointing in approximately the same direction along all three lattice planes (arrows) and within a hexagon (circle). This suggests a simple lattice. (B) EDL shows triangular profiles with variable orientations, which are analyzed below. (C–F) SOL and EDL sections at higher magnification analyzed by projection matching. (C and E) Raw images with superposed white triangles representing orientation determined by projection matching (see text). (D and F) Triangles extracted from C and E reveal orientations most clearly. (D) Triangles with similar orientations in all three planes (red rectangles) and in hexagon (circle). (F) Triangles with varying orientations, mostly following the no-three-alike rule. Scale bars, 200 nm (A and B); 100 nm (C–F).

Figure 4.. Analysis of filament orientations in one micrograph each of SOL and EDL. (A and D) Filament orientations in simple lattice (A; all filaments have same orientation; mean deviation angle = 0°) and no-three-alike superlattice (D; in any group of three filaments, in a line or forming a triangle, one filament is rotated by 60° with respect to the other two, which are identical; mean deviation angle for any three adjacent filaments = 30°). (B) Histogram for SOL micrograph showing mean deviation angle for the six filaments surrounding the central filament in a hexagon. The histogram peaks near 10°, close to the expected 0° for a simple lattice. (C) Deviation angle for adjacent filaments in SOL considered pairwise. The histogram peaks near to 0°, as expected for a simple lattice. (E) Mean deviation angle for the six filaments surrounding the central filament in a hexagon for EDL micrograph. The peak is close to 30°, as expected for a no-three-alike superlattice. (F) Deviation angle for adjacent filaments in EDL considered pairwise. There are two peaks, close to 0 and 60°, as expected for a no-three-alike superlattice (see D). Note: The relatively broad spread of the angle data is due…