Creatine kinase equilibrium and lactate content compared with muscle pH in tissue samples obtained after isometric...

Area of Science:

• Exercise Physiology
• Biochemistry
• Muscle Metabolism

Background:

• Understanding muscle energy metabolism during exercise is crucial for athletic performance and recovery.
• The creatine kinase reaction plays a vital role in maintaining cellular energy homeostasis.
• Intracellular pH changes during exercise can influence metabolic pathways.

Purpose of the Study:

• To investigate the relationship between muscle pH, high-energy phosphates, and metabolic byproducts during isometric contraction.
• To determine how changes in intracellular pH affect the creatine kinase reaction equilibrium.
• To elucidate the impact of exercise-induced metabolic shifts on muscle energy stores.

Main Methods:

• Muscle biopsies were obtained from the musculus quadriceps femoris at rest, after circulatory occlusion, and following isometric exercise to fatigue.
• Analysis included measurements of pH, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), creatine phosphate (CP), creatine, lactate, and pyruvate.
• The apparent equilibrium constant of the creatine kinase reaction (apparent K(CK)) was calculated.

Main Results:

• Muscle pH decreased significantly from 7.09 at rest to 6.56 after isometric exercise.
• A linear relationship was observed between the decrease in muscle pH and the accumulation of lactate plus pyruvate.
• An increase of 22 µmol/g muscle of lactate plus pyruvate correlated with a 0.5 pH unit drop.
• The apparent K(CK) increased post-contraction, showing a linear relationship with muscle pH.
• Low creatine phosphate levels post-exercise were attributed to altered creatine kinase equilibrium driven by pH changes.

Conclusions:

• Isometric exercise leads to a significant decrease in muscle pH, primarily driven by lactate and pyruvate accumulation.
• The observed changes in intracellular pH directly influence the equilibrium of the creatine kinase reaction.
• Altered creatine kinase equilibrium, caused by exercise-induced pH shifts, contributes to the depletion of creatine phosphate during intense muscle activity.