The Z-band lattice in a slow skeletal muscle.

Structural features of the Z-lattice were examined in cross-sections of rat soleus muscle. Optical diffraction analysis of individual myofilament bundles revealed highly ordered, tightly packed tetragonal lattice regions with abrupt shifts in orientation. Optical reconstructions of cross-sections of the Z-lattice in regions having the same axial filament spacing showed both the basket weave and the small square lattice forms, as well as intermediate structures. Analysis of these regions in three dimensions and in two-dimensional projections suggests that a change in diameter together with a change in curvature of the cross-connecting filaments can explain the different appearances of the Z-lattice at a given sarcomere length.