The Z lattice in canine cardiac muscle.

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 two distinctly different optical diffraction patterns, one for each of two lattice forms (basket weave and small square) . Other images are more complex and exhibit composite diffraction patterns . Thus, the two lattice forms co-exist, interconvert, or represent two different aspects of the same details within the lattice . Two three-dimensional models of the Z lattice are presented . Both include the following features : a double array of axial filaments spaced at 24 nm, successive layers of tetragonally arrayed connecting filaments, projected fourfold 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 two types of variation in the lattice substructure : (a) in the arrangement of connecting filaments, and (b) in the arrangement of units added side-to-side to make larger myofilament bundles and/or end-to-end to make wider Z bands . We conclude that the regular arrangement of axial and connecting filaments generates a dynamic Z lattice . KEY WORDS cardiac muscle -Z bands optical diffraction -image reconstructionIn canine cardiac muscle the Z band in longitudinal section varies in width from 80 to 160 nm and is a repeating filamentous structure with associated electron-dense material at the edge of each sarcomere. In cross sections the Z band is delineated from the surrounding sarcoplasm by vesicles of the sarcoplasmic reticulum (2), and the Z band has a repeating tetragonal unit cell (6). At J. CELL BIOLOGY

The Z-band lattice in skeletal muscle before, during and after tetanic contraction

“…different orientation. We have observed such transitions in our studies of canine cardiac muscle (Goldstein et al, 1977(Goldstein et al, , 1979. Many researchers have observed the small square and basketweave lattices occurring in Z-bands of the same axial filament spacing (Kelly & Cahill, 1972;Goldstein et al, 1982;Yamaguchi et aI., 1985).…”

“…The data show a 20% increase in the spacing of the axial filaments after the lattice change from small square to basketweave. We have previously modelled the Z structures seen in electron micrographs of 'widened' Z bands in canine cardiac muscle, in 'widened' Z-bands in skeletal muscle from a human patient with nemaline myopathy, and in normal canine cardiac muscle and rat soleus muscle on the basis of a repeating unit with four-fold symmetry (Goldstein et al, 1977(Goldstein et al, , 1979(Goldstein et al, , 1980(Goldstein et al, , 1982. This lattice structure is similar to that recently proposed by Yamaguchi et al (1985).…”

“…The small square pattern, seen in glutaraldehyde-fixed muscles (Fardeau, 1969a, b;Landon, 1970a;Franzini-Armstrong, 1973;Goldstein et al, 1982) is parallel to the I squares and divides each square into four small squares. Both patterns, basketweave and small square, are preserved after glutaraldehyde fixation (Kelly, 1967;Goldstein et al, 1979). We have shown further that both patterns can occur in a single myofibril (Goldstein et al, 1982).…”

Striated Muscle Cytoarchitecture: An Intricate Web of Form and Function

“…The rod domains of α-actinin monomers interact to establish antiparallel dimers that are capable of cross-linking actin and titin filaments from neighboring sarcomeres. The width of a Z-line can vary from ∼ 30 nm (fish skeletal muscle) to ∼ 160 nm (vertebrate cardiac muscle) (Franzini-Armstrong 1973, Goldstein et al 1979), suggesting that the configuration and/or number of the α-actinin cross-links may differ between muscles.…”

DNase I interactions with filaments of skeletal muscles

“…The axial filaments of the Z-band are continuous with but thicker than the thin filaments of the I-band (Franzini-Armstrong, 1973;Goldstein et al, 1977Goldstein et al, , 1979 suggesting that additional proteins are associated with the axial filaments. The Z-lattice also contains an additional structural element which is not found in the I-band, small diameter cross-connecting filaments which connect each axial filament to four axial filaments of the adjacent sarcomere (Goldstein et al, 1979(Goldstein et al, , 1982).…”