Isometric and isovelocity contractile performance of red musle fibres from the dogfish Scyliorhinus canicula
F. Lou1,*,
N. A. Curtin1,
and
R. C. Woledge2
1 Biological Structure and Function, Division of Biomedical Sciences,
Faculty of Medicine, Sir Alexander Fleming Building, Imperial College of
Science, Technology and Medicine, London SW7 2AZ
2 UCL Institute of Human Performance, Royal National Orthopaedic Hospital
Trust, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK
* Present address: Department of Biosciences, Faculty of Natural Sciences,
University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB,
UK
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Fig. 4. Sample recordings from the slack test measurements of
V0, the unloaded velocity of shortening from a red muscle
preparation. (A) Three superimposed recordings of tetanic force before and
after the length steps ( L) shown in B. The fibre bundle was
released by different distances from the same starting length. (C) Recordings
of force from A shown on expanded scales and with regression lines fitted to
the early part of the force redevelopment. The broken vertical lines marks the
time of the release. The horizontal arrow marks t, the time
from the release to the regression intercept for the largest step. This is the
time required to take up the slack following the length step. (D) Relationship
between step size, L, and t. The slope of the
regression line, 1.503±0.002 L0 s-1
(mean ± S.E.M., N=3), is V0 for this fibre
bundle. The intercept on the L axis,
0.053±0.0001L0 (mean ± S.E.M. N=3),
is an estimate of the compliance of the series elastic component (SEC) of this
fibre bundle. L0, the fibre length at which maximum
isometric force was produced, was 8.7 mm.
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Fig. 7. (A) Example of a stress versus strain relationship for the series
elastic component of a red fibre bundle. The points show observations from
recordings such as those shown in Fig.
5. Stress is that produced at the end of the step change in
length, and strain is the size of the step change in length. The fitted line
was calculated as described in the text. Strain, Y, is the sum of a
constant, k, a linear component, a(x), and a
saturating component, b(x), where x is stress.
Y=k+a(x)+b(x), where
a(x)=mx; if x<c, then
b(x)=nx; if x c, then
b(x)=nc. The fitted values were k=-0.0498,
m=0.0381, n=0.0625 and c=0.186. The total strain
(black line) is the sum of k (broken line) and a(x)
(red line) and b(x) (green line). (B) Corresponding strain
versus stress relationship with points and black line as in A.
L, length change; L0, fibre length at
which maximum isometric force was produced; P0, isometric
force before shortening.
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Fig. 1. (A) Video image of a transverse cryo-section of a red fibre bundle after
staining with Evans Blue. Intact fibres appear grey and damaged fibres pale.
(B) Histogram of the numbers of fibres with different cross-sectional areas
(CSA). The muscle preparation was the same as that shown in A.
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Fig. 3. Relationship between maximum tetanic force and cross-sectional area (CSA)
of intact fibres in red (filled symbols) and white (open symbols) muscle
preparations. Damaged fibres were removed as described in the text before CSA
was measured. The slopes of the lines are the mean of the force/CSA values,
142.4±10.3 kN m-2 (N=35) for red fibres and
289.2±8.4 kN m-2 (means ± S.E.M., N=25) for
white fibres.
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Fig. 5. (A) Three superimposed recordings of active force during tetanic
stimulation of a red fibre bundle shortening at different velocities. (B,C)
Force and length change (L) on an expanded time scale. The
horizontal lines in B show the forces that were measured during the period at
the start of the ramp shortening when force was relatively constant.
L0, the fibre length at which maximum isometric force was
produced, was 6.6 mm.
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Fig. 6. (A) Summary of the force/velocity results for the seven red fibre bundles
(different symbols for different bundles). Force is expressed relative to
P0, the isometric force at L0, the
fibre length at which maximum isometric force was produced, and velocity is
expressed relative to maximum shortening velocity Vmax.
Each fibre bundle's values are expressed relative to its own
P0 and Vmax. Vmax
was found for each fibre bundle by fitting a hyperbola to its force/velocity
data as described in the text. The line is the mean of these fitted lines for
the seven fibre bundles. (B) The relationship between power and velocity of
shortening. The points are the products of the force and velocity values shown
in A and the line is the mean of the calculated power curves for the seven
fibre bundles. (C) The power for both stretch and shortening. The points are
the products of the force and velocity values shown in A. The line for
shortening is the same as in B. The line for stretch is a straight line fitted
through the points and constrained to pass through the origin.
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Fig. 8. (A) Three superimposed recordings of active force during tetanic
stimulation of a red fibre bundle with stretch at different velocities. (B,C)
Force and length change (L) on expanded scales. The horizontal
lines in B show the forces that were measured during stretch. Results from the
same fibre bundle as in Fig. 5.
L0, the fibre length at which maximum isometric force was
produced, was 6.6 mm.
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Fig. 9. Comparison of the force and power output by intact white
(Curtin and Woledge, 1988 ) and
red muscle fibres. Black lines (white fibres) and red lines (red fibres) were
calculated from Hill's equation using the mean values of the fitted constants
in Table 3A (means for seven
white fibre preparations and seven red fibre preparations). (A) The
relationship between relative force and relative velocity calculated from the
following:
P'={[B(P*+A)]/(V'+B)}-A,
where P' is force expressed relative to P0,
the maximum isometric force, V' is velocity expressed relative
to Vmax, the maximum velocity of shortening, which is the
intercept of the force/velocity curve on the velocity axis.
Table 3A includes the values of
the constants:
for red fibres and 1.19±0.04 for white fibres;
A=a/P0=0.269±0.024 for red fibres
and 0.274±0.020 for white fibres;
B=b/Vmax=0.225±0.024 for red
fibres and 0.236±0.022 for white fibres. (B) The relationship between
relative power and relative velocity calculated from the following: relative
power=P'V', where P' and
V' are defined as in A. (C,D) The corresponding relationships
with force expressed in units of force per cross-sectional area and velocity
expressed in units of L0 s-1, where
L0 is the fibre length at which maximum isometric force,
P0, was produced.
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© The Company of Biologists Ltd 2002
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