Tension relaxation in frog skeletal muscle is proportional to the number of sarcomeres in series activated initially, suggesting latency relaxation may be caused by a definite elongation.
Hypothesis-generating in frog skeletal muscle; leaves open whether sarcomere-series mechanisms apply to mammalian cardiac relaxation.
Mulieri (1972) has reported that the depth of the latency relaxation, tension relaxation, changes only insignificantly when about half of a fibre bundle is wound tightly around a small glass rod. From this observation he concludes that the tension relaxation is not correlated with the number of sarcomeres in series in a frog muscle fibre. The dependency of the tension relaxation on the number of sarcomeres in series has been reinvestigated using both Mulieri's method and other independent methods. When Mulieri's experimental procedure was repeated, his result was reproduced. In the other methods used the tension relaxation was found to be proportional to the number of sarcomeres in series which were activated initially. This result was also obtained by introducing a slight modification to the procedure used by Mulieri. The results could equally well be understood if the latency relaxation was caused by a definite elongation rather than an increase in compliance of the fibre.
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Bartels et al. (1976) studied this question.
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