Skeletal muscle ECF pH error signal for exercise ventilatory control

Area of Science:

• Exercise Physiology
• Autonomic Nervous System Regulation
• Skeletal Muscle Metabolism

Background:

• Autonomic reflexes link muscle activity to breathing control.
• Neural afferents in muscle interstitial fluid are suspected mediators.
• The role of muscle extracellular fluid pH (pHe) in this reflex is unclear.

Purpose of the Study:

• To investigate if muscle pHe changes serve as an error signal for exercise ventilatory control.
• To determine if muscle pHe meets criteria for a ventilatory metaboreflex mediator.

Main Methods:

• Electrically induced skeletal muscle contraction in rats.
• Measurement of muscle intracellular and extracellular pH using 31P-magnetic resonance spectroscopy.
• Utilized phenylphosphonic acid as a pH-sensitive marker in the extracellular fluid.

Main Results:

• Muscle intracellular pH decreased significantly during stimulation.
• Muscle extracellular fluid pH (pHe) dropped immediately and remained acidic throughout exercise.
• Arterial pH showed no net change despite induced lactic acidosis and respiratory alkalosis.

Conclusions:

• Muscle extracellular fluid pH (pHe) changes during exercise meet the temporal and qualitative requirements to act as a ventilatory metaboreflex mediator.
• Muscle pHe, not arterial pH, appears to be a key signal for exercise ventilatory control.
• Ion-transport mechanisms are likely involved in regulating muscle pH during exercise.