Evidence for Two Distinct Cross-Bridge Populations in Tetanized Frog Muscle Fibers Stretched with Moderate Velocities
When a tetanized frog skeletal muscle fiber is stretched with moderate velocities (<1 L 0/s), the tension developed above the level of isometric tension starts to decay after a sudden reduction of stretch velocity by more than 40–50%, though the fiber is still being stretched. We analyzed the decay of tension responses caused by the sudden reduction of stretch velocity, by applying three different types of stretch, i.e. a 1.5% stretch with velocity V1 (stretch 1), a 1.5% stretch with velocity V2 < V1 (stretch 2), and a 3% stretch consisting of stretches 1 and 2 applied in succession (stretch 3) and comparing the corresponding tension responses, TR 1, TR 2 and TR 3. It was found that TR 3 to stretch 3 was equal to algebraical sum of TR 1 to the preceding stretch 1 and TR 2 to the subsequent stretch 2. In other words, TR 2 started on the falling tension baseline equal to the decay of TR 1 after completion of stretch 1, These results can be explained by assuming two distinct cross-bridge populations mechanically acting in parallel with each other.
KeywordsThin Filament Myosin Head Tension Response Isometric Tension Sudden Reduction
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- 2.Hill, A.V. & Howarth, J.V. Proc. Roy. Soc. B151, 169–193 (1959).Google Scholar
- 4.Huxley, A.F. Prog. Biophys. Biophys. Chem.l, 255–318 (1957).Google Scholar
- 5.Huxley, H.E. in The Cell, (eds. Brahet, J. & Mirsky, A.E.) 365–481 (Academic Press, New York, 1960)Google Scholar
- 7.Kobayashi, T., Kosuge, S., Narushima, K. & Sugi, H. submitted, 1998Google Scholar
- 9.Gasser, H.S. & Hill, A.V. Proc. Roy. Soc. B96, 398–437 (1924).Google Scholar
- 13.Kobayashi, T., Wakabayashi, K., Kosuge, S. & Sugi, H. J. Muscle Res. Cell Motil. 18, 486 (1997).Google Scholar