ISSN:
1432-1424
Keywords:
excitation-contraction coupling
;
triad junctions
;
dihydropyridine receptor
;
ryanodine receptor
;
strong triads
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870074
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