Variation in the determinants of power of chemically skinned type I rat soleus muscle fibres.
We explored to which extent maximal velocity of shortening (Vmax), force per cross-sectional area (specific tension, Po) and curvature of the force-velocity relationship (a/Po in the Hill equation) contribute to differences in peak power of single, chemically skinned rat type I fibres. Force-velocity relationships were determined from isotonic contractions of 94 maximally activated fibres. Peak power (±SD) was 3.50±1.64 WL(-1). There was a tenfold range of peak power and five-, six- and fourfold ranges for Po, Vmax and a/Po, respectively. None of the differences between fibres was explicable by differences in myosin heavy or light chain composition. The inverse relationship between a/Po and Vmax suggests a similar underlying cause. Fitting the data to the Huxley (Progr Biophys Biophys Chem 7:255-318, 1957) cross-bridge model showed that the rate constant g (2) and the sum of the rate constants (f+g(1)) co-varied, both being low in the slowest fibres. Approximately 16% of the variation in Po could be explained by variation in the proportion of attached cycling cross-bridges (f/(f+g(1))), but the origin of most of the variance in Po remains unknown.
Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, John Dalton Building, Oxford Road, Manchester M5 1GD, UK.
Sally F
SF
Gilliver
David A
DA
Jones
Jörn
J
Rittweger
Hans
H
Degens
D000818:Animals; D066298:In Vitro Techniques; D007551:Isotonic Contraction; D016018:Least-Squares Analysis; D016014:Linear Models; D008297:Male; D008954:Models, Biological; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism / Q000502:physiology*; D053580:Muscle Strength; D018995:Myosin Heavy Chains / Q000378:metabolism; D018994:Myosin Light Chains / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D018994:Myosin Light Chains; D018995:Myosin Heavy Chains