New information about the unique structural symmetry of the Z band lattice will provide insights into the contractile and elastic properties essential for adaptation of the heart. In striated heart muscle cells, the Z band is not just a link between contractile units, but an integral part of the three-dimensional contractile apparatus. We have shown that the Z band in heart and skeletal muscle has two distinct structural states and these are related to the contractile state. One lattice form (ss) is found in relaxed muscle; the other (bw) is found in an activated or tension bearing state. We have provided evidence that the Z band can serve as an elastic component in cardiac and skeletal muscle. Our 3-d reconstruction of a mammalian skeletal muscle Z band shows an even more complex filament arrangement than predicted from computer-enhanced 2-d projections. Our data indicate that the Z band modulates contraction and in the process, the lattice is rearranged. Our purpose in these studies is to begin to characterize the Z band in real time and in 3-d. We will continue to examine differences in 2-d images of the Z band lattice in adult and developing cardiac and slow skeletal muscle, and in adult fast skeletal muscle. These differences will be correlated with specific structural states of the Z band induced experimentally by altered tension, calcium or selective extraction. We will generate three dimensional reconstructions of the Z band by computerized image processing of tilt series of electron micrographs. Then we can determine the impact of specific rearrangements within the lattice in different muscle types in different physiological states. Using goniometer tilt and stereo techniques at standard and high voltages, together with optical diffraction and image enhancement, we will examine Z bands in each lattice state 1) in normal muscles frozen before and during a single twitch and after tetanic contraction; 2) in normal muscle chemically skinned, relaxed, or in rigor, and incubated with antibodies to specific Z band proteins; and 3) in postnatally developing intact muscle. The proposed analysis of the Z band will show precise structural features responsible for some of the fundamental properties of striated muscle. The new experimental approaches we are developing will help us assess function at the macromolecular level and thus understand disease at the level of protein expression.
