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The Na+,K+ pump and muscle excitability
T Clausen1, O B Nielsen, A P Harrison
1Department of Physiology, University of Aarhus, Arhus, Denmark.
Acta Physiologica Scandinavica
|May 13, 1998
Summary
Skeletal muscle excitability relies on the balance between sodium (Na+) entry and sodium-potassium (Na+,K+) pump capacity. The Na+,K+ pump dynamically maintains muscle excitability during intense activity.
Area of Science:
- Muscle Physiology
- Cellular Electrophysiology
Background:
- Mammalian skeletal muscles possess a high capacity for Na+,K+ pumps, with only 5% active at rest.
- High-frequency stimulation activates nearly all Na+,K+ pumps within seconds.
- Despite this capacity, muscle activity can lead to K+ loss, Na+ gain, and reduced excitability.
Purpose of the Study:
- To investigate the dynamic role of the Na+,K+ pump in maintaining skeletal muscle excitability during activity.
- To determine the relationship between Na+ influx, Na+,K+ pump capacity, and muscle endurance.
Main Methods:
- Analysis of Na+,K+ pump activity under varying extracellular K+ and Na+ concentrations.
- Assessment of force development and recovery during electrical stimulation.
- Investigation of the effects of ouabain on force recovery.
Main Results:
- Reduced excitability occurs with high extracellular K+ or low extracellular Na+.
- Na+,K+ pump stimulation promotes force recovery, blocked by ouabain, via hyperpolarization and gradient restoration.
- Impaired Na+,K+ pump capacity accelerates force decline and delays recovery during stimulation.
- Increased Na+ channel activity correlates with reduced endurance and impaired force recovery.
Conclusions:
- Skeletal muscle excitability during activity is critically dependent on the ratio of Na+ entry to Na+,K+ pump capacity.
- The Na+,K+ pump plays a vital, dynamic role in the rapid restoration and maintenance of excitability in working muscles.