Abstract
Changes in load during most phases of an isotonic contraction of the frog and turtle heart increased or decreased the duration of the twitch. It was abbreviated by a maintained increase or by a brief decrease in load. The relaxing effect of these procedures developed with a delay lasting more than a second under some conditions and will be called lengthening deactivation. The reverse procedures, a maintained diminution or a brief increase in load, increased the duration of the twitch. This effect will be called shortening activation. Although the termination of relaxation may be delayed or advanced by the mechanical interventions mentioned, the normal time- course of isotonic relaxation was always resumed later, regardless of the starting level of the load, making it possible to measure accurately changes in the duration of the twitch. The responses to changes in load produce positive feedback during the isotonic contraction and explain, at least in part, the difference in the time- course of isotonic and isometric contraction. The effects of changes in load were much smaller and briefer in the atrium than the ventricle.
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Selected References
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- Bozler E., Delahayes J. F. Mechanical and electrical oscillations in cardiac muscle of the turtle. J Gen Physiol. 1973 Nov;62(5):523–534. doi: 10.1085/jgp.62.5.523. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bozler E. Responses and Ca uptake of cardiac muscle in Na-free high-Ca solutions. Am J Physiol. 1971 Aug;221(2):618–622. doi: 10.1152/ajplegacy.1971.221.2.618. [DOI] [PubMed] [Google Scholar]
- HUXLEY A. F. Muscle structure and theories of contraction. Prog Biophys Biophys Chem. 1957;7:255–318. [PubMed] [Google Scholar]
- Kaufmann R. L., Lab M. J., Hennekes R., Krause H. Feedback interaction of mechanical and electrical events in the isolated mammalian ventricular myocardium (cat papillary muscle). Pflugers Arch. 1971;324(2):100–123. doi: 10.1007/BF00592656. [DOI] [PubMed] [Google Scholar]
- Weber A., Murray J. M. Molecular control mechanisms in muscle contraction. Physiol Rev. 1973 Jul;53(3):612–673. doi: 10.1152/physrev.1973.53.3.612. [DOI] [PubMed] [Google Scholar]