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First published online March 27, 2009
Journal of Experimental Biology 212, 1115-1119 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.020982
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Non-linear myofilament elasticity in frog intact muscle fibres

K. A. P. Edman

Department of Experimental Medical Science, Biomedical Centre, University of Lund, S-221 84 Lund, Sweden


Figure 1
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  		Fig. 1. Simultaneous records of force, stiffness and puller movement during load-clamp recording performed during fused tetanus of a single muscle fibre. Sarcomere length: 2.20 µm. FL=fibre length. Temperature, 2.1°C.

 

Figure 2
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  		Fig. 2. Superimposed records of force (upper) and stiffness (lower) recorded at 2.20 µm and 2.60 µm sarcomere lengths. Two different load-clamp levels are illustrated in two separate muscle fibres A and B. Load-clamp levels (fraction of tetanic force at 2.20 µm sarcomere length): A, 0.46; B, 0.59. Note that whereas the load-clamp level is the same at the two sarcomere lengths in A and B, the fibre stiffness recorded during the load-clamp phase is markedly different at the two lengths. Temperature: A, 2.0°C; B, 2.1°C.

 

Figure 3
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  		Fig. 3. The ratio of fibre stiffness recorded at 2.60 µm sarcomere length (S2.60) to that recorded at 2.20 µm sarcomere length (S2.20) plotted against the force held by the fibre during the load-clamp phase. Force is expressed as a fraction of the tetanic force measured at 2.20 µm sarcomere length. Data collected from eight individual muscle fibres with 1–3 different load-clamp levels tested in each fibre. Line: linear regression of stiffness ratio upon force. The slope of the line does not deviate from zero, P>0.5. Each data point is based on 1–3 recordings at 2.20 and 2.60 µm sarcomere length.

 

Figure 4
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  		Fig. 4. Myofilament stiffness calculated for different force levels based on data presented in Fig. 3. Open symbols: myofilament stiffness at 2.20 µm sarcomere length. Closed symbols: myofilament stiffness at 2.60 µm sarcomere length. Lines: least-squares fitting of exponential growth y=0.99exp(2.67x) (upper curve) and y=0.50exp(2.67x) (lower curve). R2=0.99. Force is expressed as a fraction of the tetanic force measured at 2.20 µm sarcomere length.

 

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© The Company of Biologists Ltd 2009