A computational model for glycogenolysis in skeletal muscle

Area of Science:

• Biochemistry
• Systems Biology
• Skeletal Muscle Physiology

Background:

• Skeletal muscle glycogenolysis is crucial for energy production during exercise.
• Understanding the dynamic regulation of this pathway is complex.
• Existing models often lack physiological relevance or detailed thermodynamic constraints.

Purpose of the Study:

• To construct a dynamic, thermodynamically valid model of the glycogenolytic pathway to lactate in skeletal muscle.
• To investigate the regulatory control of this pathway when coupled to cellular energy demands (ATPase).
• To compare muscle glycogenolysis modeling with that of other cell types.

Main Methods:

• Developed a dynamic model incorporating mammalian kinetic parameters, stoichiometric constraints, mass balance, and reversible thermodynamics.
• Validated model thermodynamics by reaching equilibrium and comparing mass action ratios to equilibrium constants.
• Integrated physiological features: fixed glycogen, lactate efflux, and ATPase coupling for steady-state flux analysis.

Main Results:

• Coupling the glycogenolytic network to an ATPase renders the system primarily ATPase-driven.
• The steady-state flux is most sensitive to external ATPase activity, rather than internal pathway enzyme kinetics.
• Internal pathway enzyme control is minor and flux-dependent, influenced by glycogen phosphorylase a levels.

Conclusions:

• The dynamic model provides a unique framework for understanding muscle glycogenolysis regulation.
• External cellular demands (ATPase activity) are dominant regulators of muscle energy flux from glycogen.
• This model highlights distinct control mechanisms in skeletal muscle compared to other cell types.