The Z lattice in canine cardiac muscle.

Open Access
Publisher Website
Google Scholar
Abstract
Filtered images of mammalian cardiac Z bands were reconstructed from optical diffraction patterns from electron micrographs. Reconstructed images from longitudinal sections show connecting filaments at each 38 nm axial repeat in an array consistent with cross-sectional data. Some reconstructed images from cross sections indicate 2 distinctly different optical diffraction patterns, 1 for each of 2 lattice forms (basket weave and small square). Other images are more complex and exhibit composite diffraction patterns. The 2 lattice forms co-exist, interconvert or represent 2 different aspects of the same details within the lattice. Two 3-dimensional models of the Z lattice are presented which include a double array of axial filaments spaced at 24 nm, successive layers of tetragonally arrayed connecting filaments, projected 4-fold symmetry in cross section, and layers of connecting filaments spaced at intervals of 38 nm along the myofibril axis. Projected views of the models are compared to electron micrographs and optically reconstructed images of the Z lattice in successively thicker cross sections. The entire Z band is rarely a uniform lattice regardless of plane of section or section thickness. Optical reconstructions strongly suggest 2 types of variation in the lattice substructure: in the arrangement of connecting filaments and in the arrangement of units added side-to-side to make larger myofilament bundles and/or end-to-end to make wider Z bands. Regular arrangement of axial and connecting filaments apparently generates a dynamic Z lattice.