Muscle cell electrical hyperpolarization and reduced exercise hyperkalemia in physically conditioned dogs

Area of Science:

• Exercise Physiology
• Cellular Electrophysiology
• Skeletal Muscle Metabolism

Background:

• Intense exercise can cause hyperkalemia (high blood potassium) due to K+ release from contracting muscles, posing cardiotoxicity risks.
• Physical training mitigates exercise-induced hyperkalemia and can lead to resting hypokalemia in highly conditioned individuals.

Purpose of the Study:

• To investigate the physiological factors responsible for reduced exercise-induced hyperkalemia and altered resting membrane potential following endurance training.
• To examine changes in serum and muscle potassium levels, and sarcolemmal Na,K-ATPase activity after a 6-week treadmill running program in dogs.

Main Methods:

• Dogs underwent a 6-week treadmill training program.
• Measurements included resting serum and muscle intracellular [K+], in vivo and in vitro muscle cell membrane potential (Em), and sarcolemmal Na,K-ATPase activity before and after training.
• Exercise tolerance tests were performed to assess serum [K+] response to exhaustive exercise.

Main Results:

• Training decreased resting serum [K+] and increased intracellular muscle [K+], hyperpolarizing the muscle cell membrane potential (Em).
• Skeletal muscle sarcolemmal Na,K-ATPase activity significantly increased post-training.
• Trained dogs showed a blunted serum [K+] elevation during exhaustive exercise compared to untrained dogs.

Conclusions:

• Endurance training induces cellular adaptations in skeletal muscle, including increased Na,K-ATPase activity and altered membrane potential.
• These adaptations contribute to the reduced risk of hyperkalemia during strenuous exercise in trained individuals.
• The precise mechanisms of cellular hyperpolarization require further investigation but likely involve enhanced Na-K exchange across the sarcolemma.