Influence of partial activation on force-velocity properties of frog skinned muscle fibers in millimolar magnesium ion.
Key result
Partial activation (developed force approximately 40% of full value) of frog skinned muscle fibers did not significantly alter relative force-velocity relations compared to full activation.
Population
Segments of briefly glycerinated muscle fibers from Rana pipiens
Comparison
Partial activation under 6 mM MgCl2 and 5 mM ATP vs Full activation under 6 mM MgCl2 and 5 mM ATP
Design
Preclinical
Authors
Discussion
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Implication
Supports activation-independent shortening in frog fibers; leaves open translation to mammalian cardiac myofilament mechanics.
Structured PICO
P
Population
Segments of briefly glycerinated muscle fibers from Rana pipiens used to study force-velocity properties.
I
Intervention
Partial activation (developed force approximately 40% of full value) under 6 mM MgCl2 and 5 mM ATP
C
Comparator
Full activation under 6 mM MgCl2 and 5 mM ATP
O
Outcome
Relative isotonic forces (P/P0) and shortening velocitiessurrogate
Shortening velocity in frog skinned muscle fibers is independent of the level of activation, supporting the hypothesis that cross-bridges act independently and calcium acts as an all-or-none switch.
Limitations
- Attempts to repeat earlier experiments using low ionic strength were unsuccessful because the fibers broke after a few contractions.
- Attempts to repeat earlier experiments by others showing a dependence of shortening velocity on activation were unsuccessful because the low ionic strength used in those experiments caused the fibers to break after a few contractions.
Cite This Study
Podolin et al. (1986) studied Frog skinned muscle fibers. Partial activation vs. Full activation was evaluated on Relative force-velocity relations. Partial activation (developed force approximately 40% of full value) of frog skinned muscle fibers did not significantly alter relative force-velocity relations compared to full activation.