Folding muscle fibers of the golfingia gouldii

Regulatory mechanism of contraction in the proboscis retractor muscle of Phascolosoma scolops was studied by physiological measurements and cytochemical electron microscopy. The magnitude of K+-contracture was dependent on external Ca2+ concentration and the contracture disappeared in Ca2+-free solution. The K+-contracture was suppressed by application of procaine and Mn2+. Caffeine induced contracture even when external Ca2+ was absent. Ultrastructural observations of the retractor muscle cells showed the presence of a large number of vesicles (subsarcolemmal vesicles), corresponding to the sarcoplasmic reticulum in vertebrate skeletal muscle, underneath the plasma membrane. For the cytochemical electron microscopy, the muscle fibers were fixed with 1% OsO4 solution containing 2% K-pyroantimonate. In the relaxed fibers, pyroantimonate precipitates were localized along the inner surface of plasma membrane and in the subsarcolemmal vesicles. In the contracting fibers, the precipitates were uniformly distributed in the myoplasm. The X-ray microanalysis revealed that the precipitates contained Ca. These results suggest that the contractile system is activated by the influx of extracellular Ca2+ as well as by the release of Ca2+ from the intracellular structures such as the inner surface of the plasma membrane and subsarcolemmal vesicles.

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Length-tension relation of single smooth muscle cells isolated from the pedal retractor muscle ofMytilus edulis

Ishii

Takahashi

1982

J Muscle Res Cell Motil

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Single smooth muscle cells were isolated with an enzymatic dispersion procedure from the pedal retractor muscle (PRM) of Mytilus edulis. The isometric tension of the isolated cell was measured by photoelectrically recording the small, elastic displacement of one of the pair of micropipettes used to hold the ends of the cell by suction. Stimulation with a 0.1 ms rectangular current pulse elicited in the cell a twitch-like contraction which was comparable to that of the whole PRM in both time course an tension per unit cross-sectional area. The length-tension relation for maximal twitches showed that the isolated cell, like the whole PRM, can generate tension over a very wide range of lengths, that is from 0.2 to more that 2.0 Ls (where Ls is the shortest length which the resting cell assumes without any slack). No persistent tension was observed in the cell stretched up to 2.0 Ls, indicating that the passive tension observed in the whole PRM is caused by extracellular material.

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Folding muscle fibers of the golfingia gouldii

Cited by 7 publications

References 7 publications

Evolution and Diversity of Nonstriated Muscles

Evolution and Diversity of Nonstriated Muscles

Regulatory mechanism of contraction in the proboscis retractor muscle of a sipunculid worm, Phascolosoma scolops

Length-tension relation of single smooth muscle cells isolated from the pedal retractor muscle ofMytilus edulis

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