ISSN:
1432-2013
Keywords:
Skinned muscle fibres, calcium activation of
;
Skinned muscle fibres, effect of Mg-ATP
;
Muscle stiffness, sarcomere length dependence
;
Muscle force
;
sarcomere length dependence
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract 1. 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. 2. 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+. 3. 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’. 4. Quick releases in the range of 0.1–0.5%L 0 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. 5. 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. 6. 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00582098
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