Abstract
Shortening causes a transient decrease, extension an increase, in activity during contractures of the frog ventricle induced by high Ca or by isosmotic K solution. This is shown by the fact that, after the immediate passive shortening, the muscle is extended under isotonic conditions when the load is diminished, and that under isometric conditions quick release causes first a rapid drop, then a further, much slower, fall of tension. Increasing the load or stretching induce the opposite effects. At low temperatures all rapid changes in length produce oscillations of low frequency. These responses are due to a sensitive feedback mechanism similar to that previously demonstrated for insect fibrillar muscle. That this mechanism comes into play in the heart under normal conditions and controls the time-course of the twitch is demonstrated by the observation that relaxation begins earlier the greater the shortening. Thus, during afterloaded isotonic twitches the onset of relaxation is advanced as the load is diminished.
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Selected References
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- Brady A. J. Active state in cardiac muscle. Physiol Rev. 1968 Jul;48(3):570–600. doi: 10.1152/physrev.1968.48.3.570. [DOI] [PubMed] [Google Scholar]
- Edman K. A., Kiessling A. The time course of the active state in relation to sarcomere length and movement studied in single skeletal muscle fibres of the frog. Acta Physiol Scand. 1971 Feb;81(2):182–196. doi: 10.1111/j.1748-1716.1971.tb04891.x. [DOI] [PubMed] [Google Scholar]
- GOODALL M. C. Auto-oscillations in extracted muscle fibre systems. Nature. 1956 Jun 30;177(4522):1238–1239. doi: 10.1038/1771238b0. [DOI] [PubMed] [Google Scholar]
- LORAND L., MOOS C. Auto-oscillations in extracted muscle fibre systems. Nature. 1956 Jun 30;177(4522):1239–1239. doi: 10.1038/1771239a0. [DOI] [PubMed] [Google Scholar]
- Pringle J. W. The contractile mechanism of insect fibrillar muscle. Prog Biophys Mol Biol. 1967;17:1–60. doi: 10.1016/0079-6107(67)90003-x. [DOI] [PubMed] [Google Scholar]
- Rüegg J. C., Steiger G. J., Schädler M. Mechanical activation of the contractile system in skeletal muscle. Pflugers Arch. 1970;319(2):139–145. doi: 10.1007/BF00592492. [DOI] [PubMed] [Google Scholar]