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Fig. 5. The interaction of ATP turnover rate, diffusion distance and the
effectiveness factor (
), which is the ratio of the reaction rate in the
presence of diffusion to the rate if diffusion were not limiting. The surface
was generated from a Loess fit to output from a simplified
reaction–diffusion model with linear expressions for ATP production
(mitochondria), ATP consumption (ATPases) and diffusion (see text for
additional details). The symbols represent the positions on the surface of a
variety of anaerobic (white) and aerobic (red) muscle fibers from insects (bee
flight muscle) (diamonds), crustaceans (circles), fishes (squares), amphibians
(frog lumbrical muscle) (inverted triangle), reptiles (including rattlesnake
tailshaker muscle) (crosses), bird (hummingbird flight muscle) (triangle), and
mammals (pentagons). The white lines are developmental trajectories from
individual species for white muscle fibers that grow hypertrophically (muscles
are, in order from low to high ATP turnover rate: blue crab light levator,
black sea bass white epaxial muscle, pink shrimp abdominal flexor and grass
shrimp abdominal flexor). The black arrow indicates the impact of subdividing
the large aerobic fibers of blue crabs, which greatly reduces the
intracellular diffusion distances and alleviates diffusion limitation
associated with the hypothetical, non-subdivided case (value with a low )
(see text for additional details). Diffusion distances were taken from direct
measurements or calculated as in Tyler and Sidell
(Tyler and Sidell, 1984) from
the mitochondrial volume density and mitochondrial surface density [the latter
was calculated assuming a mitochondrial surface area to volume ratio of 6 if
not directly measured (Tyler and Sidell,
1984)]. ATP turnover rates per volume of muscle fiber were
determined from direct measurements of O2 consumption in tissue,
isolated fibers, or isolated mitochondria assuming 22.4 l O2
mol–1 O2, an ATP/O2 ratio of 6, and an
intracellular water content that was 70% of wet mass. For cases where
measurements of O2 consumption were unavailable, ATP turnover rate
was estimated from mitochondrial volume density assuming a sustainable rate of
O2 consumption of 3 ml min–1 cm–3
of mitochondrial volume [(Schwerzmann et
al., 1989); this value was not applied to mitochondria with known
high cristae surface densities]. Data are from the published literature
(Tyler and Sidell, 1984;
Andersen and Saltin, 1985;
Egginton and Sidell, 1989;
Schwerzmann et al., 1989;
Stokes and Josephson, 1992;
Curtin et al., 1997;
Conley and Lindstedt, 1998;
Johnston et al., 1998;
Suarez, 1998;
Egginton et al., 2000;
Vicini and Kushmerick, 2000;
Kanatous et al., 2002;
Boyle et al., 2003;
Kindig et al., 2003;
Johnson et al., 2004;
Stary et al., 2004;
Kinsey et al., 2005;
Hardy et al., 2006;
Nyack et al., 2007) and
personal observations (S.T.K., unpublished results). In studies of ectotherms
from different temperature regimes, only data from the warm acclimated or
adapted groups were included.
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