Contractile Properties of Actomyosin Threads and Bands Prepared From Dogs' Hearts

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Abstract
The experiments deal with the results obtained on the contraction of actomyosin from dogs' hearts, using a newly developed ‘null-seeking’ device for measuring and recording ATP-induced isometric, isontonic and afterloaded contractions. A comparison was made of the relative shortening of actomyosin a) when the relative shortening of actomyosin threads was plotted against the load, b) when relative shortening of the threads was expressed as a function of their specific nitrogen content, c) when this relationship was determined for compressed actomyosin bands rather than threads. In several experiments, the tension developed during isometric contraction was related to specific nitrogen content. Results demonstrate that the scatter of observation was reduced by compression of the fibers to bands and by mounting the bands in a horizontal position when recording their contractions. Using afterloaded contractions, a definite inverse relationship was found in bands between shortening and load/unit of nitrogen.

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