TY - JOUR
T1 - Isometric and isovelocity contractile performance of red musle fibres
from the dogfish <em>Scyliorhinus canicula</em>
JF - Journal of Experimental Biology
JO - J. Exp. Biol.
SP - 1585
LP - 1595
VL - 205
IS - 11
AU - Lou, F.
AU - Curtin, N. A.
AU - Woledge, R. C.
Y1 - 2002/06/01
UR - http://jeb.biologists.org/content/205/11/1585.abstract
N2 - Maximum isometric tetanic force produced by bundles of red muscle fibres from dogfish, Scyliorhinus canicula (L.), was 142.4±10.3 kN m-2 (N=35 fibre bundles); this was significantly less than that produced by white fibres 289.2±8.4 kN m-2 (N=25 fibre bundles) (means ± S.E.M.). Part, but not all, of the difference is due to mitochondrial content. The maximum unloaded shortening velocity, 1.693±0.108 L0 s-1 (N=6 fibre bundles), was measured by the slack-test method. L0 is the length giving maximum isometric force. The force/velocity relationship was investigated using a step-and-ramp protocol in seven red fibre bundles. The following equation was fitted to the data: [(P/P0)+(a/P0)](V+b)=[(P0*/P0)+(a/P0)]b, where P is force during shortening at velocity V, P0 is the isometric force before shortening, and a, b and P0* are fitted constants. The fitted values were P0*/P0=1.228±0.053, Vmax=1.814±0.071 L0 s-1, a/P0=0.269±0.024 and b=0.404±0.041 L0 s-1 (N=7 for all values). The maximum power was 0.107±0.005P0Vmax and was produced during shortening at 0.297±0.012Vmax. Compared with white fibres from dogfish, the red fibres have a lower P0 (49%) and Vmax (48%), but the shapes of the force/velocity curves are similar. Thus, the white and red fibres have equal capacities to produce power within the limits set by the isometric force and maximum velocity of shortening of each fibre type. A step shortening of 0.050±0.003L0 (N=7) reduced the maximum isometric force in the red fibres' series elasticity to zero. The series elasticity includes all elastic structures acting in series with the attached cross-bridges. Three red fibre bundles were stretched at a constant velocity, and force (measured when length reached L0) was 1.519±0.032P0. In the range of velocities used here, -0.28 to -0.63Vmax, force varied little with the velocity.
ER -