A comparison of the Three-Dimensional structures of Z bands in unstimulated and rigor skeletal muscle

Abstract

Previous studies (reviewed in ref. 1) lead to the expectation that Z bands from unstimulated skeletal muscle exhibit the unactivated small square form of the Z band lattice. Rigor Z bands, on the other hand are expected to exhibit the basket-weave form of the Z band lattice associated with activation in skeletal muscle. This Z band structural transition has been investigated by three-dimensional reconstruction of Z bands and nearby I bands in unstimulated and rigor rat soleus muscle. The reconstructions were calculated using the tomographic method of weighted back-projection on a series of electron micrographs of longitudinal thin sections of muscle.Examination of Z band cross-sections of the reconstructions reveals that the unstimulated muscle does indeed exhibit the expected small square lattice form. Furthermore, Z band cross sections of the rigor reconstructions reveal the expected basket-weave lattice form. The lattice dimensions were 20 +- 1 nra for the small square lattice and 27 +- 4 nm for the basket-weave lattice, consistent with the results from electron micrographs of cross-sections.