ISSN:
1432-0878
Keywords:
Skeletal muscle
;
Branchiostoma lanceolatum
;
Fibre types
;
Sarcoplasmic reticulum
;
Sarcolemma
;
Calcium
;
X-ray micro-analysis
;
Freeze-fracturing
;
Replica
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The trunk muscle lamellae of Amphioxus is made up of cross-striated lamellae about 1 μm thick. Transverse tubules are absent, but numerous subsarcolemmal vesicles are found in both tissue blocks and minced samples after aldehyde and osmium fixation, embedding and sectioning. The vesicles contain a granular matrix, range in diameter from 30 to 200 nm and constitute about 3 to 6% of the muscle fibre volume. 8 out of 10 vesicles are found above the Z and I-bands. In the presence of oxalate, electron dense precipitates form within the vesicles. Energy-dispersive X-ray microanalysis reveals the presence of Calcium in these precipitates. The area of the plasma membrane is about 2 μm2/μm3 muscle fibre volume. The corresponding area of sarcoplasmic membrane is ca. 1 μm2/μm3. About 20% of the plasma membrane is directly overlaid and coupled to the sarcoplasmic vesicles. A thin surface coat is present all over the lamellae, but ruthenium red staining indicates that the coat is slightly concentrated above the sarcoplasmic vesicles. Freeze-fracture replicas reveal tightly packed coarse granular material in the vesicular membrane and less concentrated and smaller particles in the plasma membrane. The latter particles are seen somewhat less commonly above the vesicles than on the rest of the plasma membrane. Likewise, direct replicas of lamella spread on glass slides and freeze-dried, reveal a distinct pattern in the surface coat or its underlying structures, corresponding to the Z and I-bands. In the scanning electron microscope the general arrangement of the sarcoplasmic vesicles could be examined. In addition, numerous defects in the plasma- and vesicular membranes indicate a strong adhesion between the two. It is concluded that the trunk muscle lamellae of Amphioxus have a sarcoplasmic reticulum consisting of subsarcolemmal vesicles with calcium sequestrating properties at Z and I-level. Further that the plasma membrane and its surface coat is probably specialized above the vesicles as compared to the rest of the surface.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00219979
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