Dependence of force and immediate stiffness on sarcomere length and Ca2+ activation in frog skinned muscle fibres
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Skinned fibres prepared from semitendinosus muscle of the frog (Rana temporaria) by a modified Natori's method were suspended in ATP-salt solution (pCa 5, pH 6.7, 3°C). Isometric tension was studied as a function of sarcomere length (determined by laser diffraction) and stiffness was measured by recording tension changes in response to quick changes in length performed within 0.5 ms during Ca2+ activated contractions.
There was a sigmoidal relationship between contractile tension or stiffness and pCa. The threshold Ca ion concentration was 5×10−7 M at a sarcomere length of 2.2 μm and a little lower at larger sarcomere lengths (as also described by Endo 1972). At all sarcomere lengths peak tension was reached at about 10−5 M Ca2+.
The skinned fibres produced maximum tension at sarcomere lengths of 2.0–2.3 μm. With a further increase in sarcomere length, contractile tension decreased. The relation between tension and sarcomere length was linear up to 3.2 μm above which value the relationship ‘tailed’.
Quick releases in the range of 0.1–0.5%L0 applied during Ca2+ activation produced an immediate elastic fall in tension in phase with the length change followed by a quick recovery phase completed within about 10 ms. Conversely, a quick stretch produced an elastic increase followed by a rapid tension decay completed within about 8–10 ms. When the extreme tensions obtained during the length step were plotted versus the size of the length step, a force-extension diagram was obtained corresponding to the T1-curve of Huxley and Simmons (1973) which intercepted the length axis at about −8 nm/half sarcomere at all sarcomere lengths investigated. The slope of the linear portion of the T1-curve was taken to determine immediate stiffness which was proportional to tension when either sarcomere length or Ca2+ ion concentration were varied.
In conclusion tension and immediated stiffness are proportional to the extent of actin myosin filament overlap and hence to the number of possible crossbridges between thick and thin filaments.
At very low calcium ion concentrations (10−7 M) skinned fibres develop tension and become stiff when the Mg-ATP concentration is lowered (at constant [ATP] total) to values below 10−5 M. Under these conditions a quick release causes a drop in tension which is—as in the case of rigor—not followed by a fast recovery of tension. Again stiffness was independent of the direction and amplitude of quick length changes; but — as in the case of rigor — the stiffness to tension ratio was much higher than in Ca2+ activated contraction.
Key wordsSkinned muscle fibres, calcium activation of Skinned muscle fibres, effect of Mg-ATP Muscle stiffness, sarcomere length dependence Muscle force sarcomere length dependence
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- Bressler BH, Clinch NF (1974) The compliance of contracting skeletal muscle. J Physiol (Lond) 237:477–493Google Scholar
- Endo M (1972) Stretch-induced increase in activation of skinned muscle fibres by calcium. Nature New Biol 237:211–213Google Scholar
- Flitney FW, Hirst DG (1978) Cross-bridge detachment and sarcomere “give” during stretch of active frog's muscle. J Physiol (Lond) 276:446–465Google Scholar
- Ford LE, Huxley AF, Simmons RM (1977) Tension responses to sudden length change in stimulated frog muscle fibres near slack length. J Physiol (Lond) 269:441–515Google Scholar
- Gordon AM, Huxley AF, Julian FJ (1966a) Tension development in highly stretched vertebrate muscle fibres. J Physiol (Lond) 184:143–169Google Scholar
- Gordon AM, Huxley AF, Julian FJ (1966b) The variation in isometric tension with sarcomere length in vertebrate muscle fibres. J Physiol (Lond) 184:170–192Google Scholar
- Griffiths PJ, Kuhn HJ, Rüegg JC (1979a) Activation of the contractile system of insect fibrillar muscle at very low concentrations of Mg2+ and Ca2+. Pfügers Arch 382:155–163Google Scholar
- Griffiths PJ, Kuhn HJ, Güth K, Rüegg JC (1979b) Rate of isometric tension development in relation to calcium binding of skinned muscle fibres. Pflügers Arch 382:165–170Google Scholar
- Güth K, Kuhn HJ (1978) Stiffness and tension during and after sudden length changes of glycerinated rabbit psoas muscle fibres. Biophys Struct Mech 4:223–236Google Scholar
- Heinl P, Kuhn HJ, Rüegg JC (1974) Tension responses to quick length changes of glycerinated skeletal muscle fibres from the frog and tortoise. J Physiol (Lond) 237:243–258Google Scholar
- Hellam DC, Podolsky RJ (1969) Force measurements in skinned muscle fibres. J Physiol (Lond) 200:807–819Google Scholar
- Huxley AF, Simmons RM (1973) Mechanical transients and the origin of muscular force. Cold Spring Harbor Symp Quant Biol 37:669–680Google Scholar
- Huxley AF, (1974) Muscular contraction. J Physiol (Lond) 243:1–43Google Scholar
- Jewell BR, Rüegg JC (1966) Oscillatory contraction of insect fibrillar muscle after glycerol extraction. Proc R Soc (Lond) 164B:4280459Google Scholar
- Julian FJ, Morgan DL (1979) Comparison of tension transients in frog twitch and slow fibres. J Physiol (Lond) 301:72–73PGoogle Scholar
- ter Keurs HEDI, Iwazumi T, Pollack GH (1979) The length tension relation in skeletal muscle — Revisited. In: Sugi H, Pollack GH (eds) Cross-bridge mechanism in muscle contraction. University of Tokyo Press, Tokyo, p 277Google Scholar
- Podolsky RJ, Teichholz LE (1970) The relation between calcium and contraction kinetics in skinned muscle fibres. J Physiol (Lond) 211:19–35Google Scholar
- Rack FHH, Westbury DR (1969) The effects of length and stimulus rate on tension in the isometric cat soleus muscle. J Physiol (Lond) 204:443–460Google Scholar
- Renben JP, Brandt PW, Berman M, Grundfest H (1971) Regulation of tension in the skinned crayfish muscle fibre. I. Contraction and relaxation in the absence of Ca. J Gen Physiol 57:387–408Google Scholar
- Rüegg JC, Güth K, Kuhn HJ, Herzig JW, Griffiths PJ, Yamamoto T (1979) Muscle stiffness in relation to tension development of skinned striated muscle fibres. In: Sugi H, Pollack GH (eds) Cross-bridge mechanism in muscle contraction. University of Tokyo Press, Tokyo, p 125–143Google Scholar
- Schädler M (1967) Proportionale Aktivierung von ATPase-aktivität und Kontraktionsspannung durch Calciumionen in isolierten contractilen Strukturen verschiedener Muskelarten. Pflügers Arch Ges Physiol 296:70–90Google Scholar
- Schoenberg M, Podolsky RJ (1972) Length force relation of calcium activated muscle fibres. Science 176:52–54Google Scholar
- Yamamoto T, Herzig JW (1978) Series elastic properties of skinned muscle fibres in contraction and rigor. Pflügers Arch, 373:21–24Google Scholar