Key Points
- To determine the relationship between the degree of thick and thin myofilament overlap and the rate of magnesium-activated ATP hydrolysis at pH 7.3.
- Prepared glycerol-extracted frog skeletal muscle fiber bundles capable of contracting in the presence of ATP.
- Assayed magnesium-activated ATPase activity at pH 7.3 across muscle bundles held at resting length and stretched to various lengths beyond rest.
- Determined sarcomere lengths in unfixed, uncontracted bundles via phase microscopy and assessed filament overlap using electron microscopy.
- Evaluated the structural model of muscle contraction wherein actin filaments interact with myosin bridges to accelerate ATP hydrolysis.
- Assessed changes in the rate of ATP cleavage as filament overlap altered across varying degrees of mechanical muscle stretch.
Structured PICO
PPopulationGlycerol-extracted skeletal muscle bundles from adult frogs (Rana pipiens)
IInterventionStretching to various lengths beyond rest length (sarcomere lengths 2.2 to 5.5 µm)
CComparatorUnstretched muscle bundles (approximately rest length)
OOutcomeRate of Mg++ activated ATP hydrolysis (ATPase activity) at pH 7.3surrogate
Demonstrates that ATPase activity in skeletal muscle depends on the amount of overlap between thick and thin myofilaments, providing mechanistic support for the sliding-filament model of contraction.