Key result
In rabbit slow-twitch muscle fibers, maximum shortening velocity showed Michaelian saturation with a Km of 18 microM and Vmax of 0.6 lengths/s, compared to 150 microM and 1.6 lengths/s in psoas.
Population
Glycerinated rabbit slow-twitch muscle fibers (semimembranosus and soleus) and fast-twitch psoas muscle
Comparison
Varying MgATP concentration vs Fast-twitch psoas muscle
Design
Preclinical
Authors
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May reverse fiber-type velocity hierarchy at low MgATP; leaves open translation to human physiology and in vivo conditions.
At low, nonphysiological MgATP concentrations, fast-twitch muscle actually has a lower shortening velocity than slow-twitch muscle due to a 10-fold difference in Km.
Pate et al. (1992) studied this question. MgATP concentration vs. Fast-twitch psoas muscle was evaluated on Maximum shortening velocity (Vmax) and Michaelis constant (Km). In rabbit slow-twitch muscle fibers, maximum shortening velocity showed Michaelian saturation with a Km of 18 microM and Vmax of 0.6 lengths/s, compared to 150 microM and 1.6 lengths/s in psoas.
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