Key Points
- To determine how inorganic phosphate influences the kinetics of endothermic force generation in single muscle fibres.
- Applied a rapid (~0.2 ms) laser temperature jump from approximately 9°C to 12°C to single-skinned rabbit psoas muscle fibres.
- Measured steady force and force-generation rates across varying concentrations of added inorganic phosphate ranging from 0 to ~25 mM.
- Increasing inorganic phosphate from 0 to ~25 mM reduced steady force while accelerating the apparent rate constant of temperature-induced force generation by two- to threefold.
- The relationship between inorganic phosphate concentration and the apparent rate constant exhibited a hyperbolic saturation pattern.
- Kinetic data aligned with a three-step sequential mechanism involving a pre-force stereospecific transition, endothermic force generation, and rapid phosphate release.
Structured PICO
PPopulationSingle-skinned (rabbit psoas) muscle fibres
IInterventionExposure to different levels of inorganic phosphate (up to ca. 25 mM) combined with a standard temperature jump (from ca. 9 degrees C to ca. 12 degrees C)
CComparatorZero added inorganic phosphate
OOutcomeRate of endothermic force generation (apparent rate constant)surrogate
Inorganic phosphate release from attached cross-bridges in active muscle fibres involves three reversible and sequentially faster molecular steps, influencing endothermic force generation.