title: Electron microscopy and x-ray diffraction evidence for two Z-band structural states.
abstract: In vertebrate muscles, Z-bands connect adjacent sarcomeres, incorporate several cell signaling proteins, and may act as strain sensors. Previous electron microscopy (EM) showed Z-bands reversibly switch between a relaxed, "small-square" structure, and an active, "basketweave" structure, but the mechanism of this transition is unknown. Here, we found the ratio of small-square to basketweave in relaxed rabbit psoas muscle varied with temperature, osmotic pressure, or ionic strength, independent of activation. By EM, the A-band and both Z-band lattice spacings varied with temperature and pressure, not ionic strength; however, the basketweave spacing was consistently 10% larger than small-square. We next sought evidence for the two Z-band structures in unfixed muscles using x-ray diffraction, which indicated two Z-reflections whose intensity ratios and spacings correspond closely to the EM measurements for small-square and basketweave if the EM spacings are adjusted for 20% shrinkage due to EM processing. We conclude that the two Z-reflections arise from the small-square and basketweave forms of the Z-band as seen by EM. Regarding the mechanism of transition during activation, the effects of Ca(2+) in the presence of force inhibitors suggested that the interconversion of Z-band forms was correlated with tropomyosin movement on actin.
authors.affiliation: Department of Cell Biology, Duke University, Durham, North Carolina, USA. rjpe@cellbio.duke.edu
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Perz-Edwards
authors.forename: Michael K
authors.initials: MK
authors.lastname: Reedy
mesh_terms: D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology; D008854:Microscopy, Electron; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism; D009126:Muscle Relaxation / Q000187:drug effects; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D016658:Psoas Muscles / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D011817:Rabbits; D015203:Reproducibility of Results; D013696:Temperature; D019209:Troponin C / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology; D014961:X-Ray Diffraction
chemical_list: D017607:Aluminum Compounds; D019209:Troponin C; D014638:Vanadates; D005459:Fluorides; D002118:Calcium; C032311:aluminum fluoride