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. 1984 Nov 1;99(5):1735–1742. doi: 10.1083/jcb.99.5.1735

Subunit structure of junctional feet in triads of skeletal muscle: a freeze-drying, rotary-shadowing study

PMCID: PMC2113360  PMID: 6386826

Abstract

Isolated heavy sarcoplasmic reticulum vesicles retain junctional specializations (feet) on their outer surface. We have obtained en face three-dimensional views of the feet by shadowing and replicating the surfaces of freeze-dried isolated vesicles. Feet are clearly visible as large structures located on raised platforms. New details of foot structure include a four subunit structure and the fact that adjacent feet do not abut directly corner to corner but are offset by half a subunit. Feet aligned within rows were observed to be rotated at a slight angle off the long axis of the row creating a center-to-center spacing (32.5 nm) slightly less than the average diagonal of the feet (35.3 nm). Comparison with previous information from thin sections and freeze-fracture showed that this approach to the study of membranes faithfully preserves structure and allows better visualization of surface details than either thin-sectioning or negative-staining.

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Selected References

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  1. Brunschwig J. P., Brandt N., Caswell A. H., Lukeman D. S. Ultrastructural observations of isolated intact and fragmented junctions of skeletal muscle by use of tannic acid mordanting. J Cell Biol. 1982 Jun;93(3):533–542. doi: 10.1083/jcb.93.3.533. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Cadwell J. J., Caswell A. H. Identification of a constituent of the junctional feet linking terminal cisternae to transverse tubules in skeletal muscle. J Cell Biol. 1982 Jun;93(3):543–550. doi: 10.1083/jcb.93.3.543. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Campbell K. P., Franzini-Armstrong C., Shamoo A. E. Further characterization of light and heavy sarcoplasmic reticulum vesicles. Identification of the 'sarcoplasmic reticulum feet' associated with heavy sarcoplasmic reticulum vesicles. Biochim Biophys Acta. 1980 Oct 16;602(1):97–116. doi: 10.1016/0005-2736(80)90293-x. [DOI] [PubMed] [Google Scholar]
  4. Castellani L., Hardwicke P. M. Crystalline structure of sarcoplasmic reticulum from scallop. J Cell Biol. 1983 Aug;97(2):557–561. doi: 10.1083/jcb.97.2.557. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Caswell A. H., Lau Y. H., Garcia M., Brunschwig J. P. Recognition and junction formation by isolated transverse tubules and terminal cisternae of skeletal muscle. J Biol Chem. 1979 Jan 10;254(1):202–208. [PubMed] [Google Scholar]
  6. Eisenberg B. R., Eisenberg R. S. The T-SR junction in contracting single skeletal muscle fibers. J Gen Physiol. 1982 Jan;79(1):1–19. doi: 10.1085/jgp.79.1.1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Endo M., Iino M. Specific perforation of muscle cell membranes with preserved SR functions by saponin treatment. J Muscle Res Cell Motil. 1980 Mar;1(1):89–100. doi: 10.1007/BF00711927. [DOI] [PubMed] [Google Scholar]
  8. Flicker P. F., Wallimann T., Vibert P. Electron microscopy of scallop myosin. Location of regulatory light chains. J Mol Biol. 1983 Sep 25;169(3):723–741. doi: 10.1016/s0022-2836(83)80167-3. [DOI] [PubMed] [Google Scholar]
  9. Fowler W. E., Aebi U. Preparation of single molecules and supramolecular complexes for high-resolution metal shadowing. J Ultrastruct Res. 1983 Jun;83(3):319–334. doi: 10.1016/s0022-5320(83)90139-9. [DOI] [PubMed] [Google Scholar]
  10. Franzini-Armstrong C. Membrane particles and transmission at the triad. Fed Proc. 1975 Apr;34(5):1382–1389. [PubMed] [Google Scholar]
  11. Franzini-Armstrong C., Nunzi G. Junctional feet and particles in the triads of a fast-twitch muscle fibre. J Muscle Res Cell Motil. 1983 Apr;4(2):233–252. doi: 10.1007/BF00712033. [DOI] [PubMed] [Google Scholar]
  12. Frey T. G., Costello M. J., Karlsson B., Haselgrove J. C., Leigh J. S. Structure of the cytochrome c oxidase dimer. Electron microscopy of two-dimensional crystals. J Mol Biol. 1982 Nov 25;162(1):113–130. doi: 10.1016/0022-2836(82)90164-4. [DOI] [PubMed] [Google Scholar]
  13. HALL C. E. Method for the observation of macromolecules with the electron microscope illustrated with micrographs of DNA. J Biophys Biochem Cytol. 1956 Sep 25;2(5):625–628. doi: 10.1083/jcb.2.5.625. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Herbette L., Marquardt J., Scarpa A., Blasie J. K. A direct analysis of lamellar x-ray diffraction from hydrated oriented multilayers of fully functional sarcoplasmic reticulum. Biophys J. 1977 Nov;20(2):245–272. doi: 10.1016/S0006-3495(77)85547-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Heuser J. E., Salpeter S. R. Organization of acetylcholine receptors in quick-frozen, deep-etched, and rotary-replicated Torpedo postsynaptic membrane. J Cell Biol. 1979 Jul;82(1):150–173. doi: 10.1083/jcb.82.1.150. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Kelly D. E., Kuda A. M. Subunits of the triadic junction in fast skeletal muscle as revealed by freeze-fracture. J Ultrastruct Res. 1979 Aug;68(2):220–233. doi: 10.1016/s0022-5320(79)90156-4. [DOI] [PubMed] [Google Scholar]
  17. Kelly D. E. The fine structure of skeletal muscle triad junctions. J Ultrastruct Res. 1969 Oct;29(1):37–49. doi: 10.1016/s0022-5320(69)80054-7. [DOI] [PubMed] [Google Scholar]
  18. Lau Y. H., Caswell A. H., Brunschwig J. P. Isolation of transverse tubules by fractionation of triad junctions of skeletal muscle. J Biol Chem. 1977 Aug 10;252(15):5565–5574. [PubMed] [Google Scholar]
  19. Meissner G., Conner G. E., Fleischer S. Isolation of sarcoplasmic reticulum by zonal centrifugation and purification of Ca 2+ -pump and Ca 2+ -binding proteins. Biochim Biophys Acta. 1973 Mar 16;298(2):246–269. doi: 10.1016/0005-2736(73)90355-6. [DOI] [PubMed] [Google Scholar]
  20. Meissner G. Isolation and characterization of two types of sarcoplasmic reticulum vesicles. Biochim Biophys Acta. 1975 Apr 21;389(1):51–68. doi: 10.1016/0005-2736(75)90385-5. [DOI] [PubMed] [Google Scholar]
  21. Mitchell R. D., Saito A., Palade P., Fleischer S. Morphology of isolated triads. J Cell Biol. 1983 Apr;96(4):1017–1029. doi: 10.1083/jcb.96.4.1017. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Schnapp B. J., Reese T. S. Cytoplasmic structure in rapid-frozen axons. J Cell Biol. 1982 Sep;94(3):667–669. doi: 10.1083/jcb.94.3.667. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Shotton D. M., Burke B. E., Branton D. The molecular structure of human erythrocyte spectrin. Biophysical and electron microscopic studies. J Mol Biol. 1979 Jun 25;131(2):303–329. doi: 10.1016/0022-2836(79)90078-0. [DOI] [PubMed] [Google Scholar]
  24. Somlyo A. V. Bridging structures spanning the junctioning gap at the triad of skeletal muscle. J Cell Biol. 1979 Mar;80(3):743–750. doi: 10.1083/jcb.80.3.743. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Stewart M., Kensler R. W., Levine R. J. Structure of Limulus telson muscle thick filaments. J Mol Biol. 1981 Dec 15;153(3):781–790. doi: 10.1016/0022-2836(81)90418-6. [DOI] [PubMed] [Google Scholar]

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