Three-Dimensional Reconstruction reconstruction of A Z band from rigor skeletal muscle

Abstract

We have produced three dimensional reconstructions of several regions of the Z band and the nearby I band in rat soleus muscle in rigor. The reconstructions were calculated using weighted back-projection techniques on electron micrograph tilt series taken about two orthogonal axes. Examination of cross-sections of the reconstructed Z bands reveal that the lattice is in the basket-weave form. We have previously shown that this form of the Z band lattice predominates in the muscle in rigor. The reconstructions reveal a dense net of cross-connecting Z-filaments in the Z band, which interconnect the axial filaments in a projected four-fold array.The Z band lattice spacing was measured as 27 +− 4 nm, consistent with values seen in electron micrographs of cross sections of this muscle. The Z spacing and the form of the lattice show little distortion from that observed in cross sections, despite a beam induced change in section thickness from ∼80 to 45 nm. This suggests that, as in previous Z band reconstructions in unstimulated muscle, section shrinkage in the Z band does not occur by means of a uniform collapse throughout the section.