The Journal of Membrane Biology

, Volume 113, Issue 3, pp 221–235

Identification of a new subpopulation of triad junctions isolated from skeletal muscle; Morphological correlations with intact muscle

  • Kyungsook C. Kim
  • Anthony H. Caswell
  • J. -P. Brunschwig
  • Neil R. Brandt
Articles

DOI: 10.1007/BF01870074

Cite this article as:
Kim, K.C., Caswell, A.H., Brunschwig, J.P. et al. J. Membrain Biol. (1990) 113: 221. doi:10.1007/BF01870074

Summary

It has been previously recognized that a number of protocols may cause breakage of the triad junction and separation of the constituent organelles of skeletal muscle. We now describe a fraction of triad junctions which is refractory to the known protocols for disruption. Triads were passed through a French press and the dissociated organelles were separated on a sucrose density gradient, which was assayed for PN200-110, ouabain and ryanodine binding. Ryanodine binding showed a single peak at the density of heavy terminal cisternae. On the other hand, the PN200-110 and ouabain, which are external membrane ligands, bound in two peaks: one at the free transverse tubule region and the other at the light terminal cisternae. Similarly, a two peak pattern of PN200-110 and ouabain binding was observed when triad junctions were broken by the Ca2+-dependent protease, calpain, which selectively hydrolyzes the junctional foot protein. The light terminal cisternae vesicles were subjected to three different procedures of junctional breakage: French press, hypertonic salt treatment, and protease digestion using calpain or trypsin. The treated membranes were then centrifuged on density gradients. Only extensive trypsin digestion caused a partial shift of ouabain activity into the free transverse tubule region. These observations suggest that the triads are a composite mixture of breakage susceptible, “weak,” and breakage resistant, “strong,” triads. Scatchard analysis of PN200-110 suggests that the transverse tubules of strong triads contain a relatively high number of dihydropyridine receptors compared to those of weak triads. Thin section electron microscopic images of the strong triads comparable to those of intact muscle are presented.

Key words

excitation-contraction coupling triad junctions dihydropyridine receptor ryanodine receptor strong triads 

Copyright information

© Springer-Verlag New York Inc. 1990

Authors and Affiliations

  • Kyungsook C. Kim
    • 1
  • Anthony H. Caswell
    • 1
  • J. -P. Brunschwig
    • 1
  • Neil R. Brandt
    • 1
  1. 1.Department of PharmacologyUnviersity of Miami, School of MedicineMiami