This study was supported by The Norwegian Research Council, Anders Jahre's Fund for the Promotion of Science, The Laerdal Foundation for Acute Medicine, The Norwegian Air Ambulance Service, and Rakel and Otto Kr. Bruun's legacy.
Fuzzy space and control of Na+, K+-pump rate in heart and skeletal muscle
Article first published online: 6 NOV 2003
Scandinavian Physiological Society
Acta Physiologica Scandinavica
Volume 156, Issue 3, pages 213–225, March 1996
How to Cite
SEMB, S. O. and SEJERSTED, O. M. (1996), Fuzzy space and control of Na+, K+-pump rate in heart and skeletal muscle . Acta Physiologica Scandinavica, 156: 213–225. doi: 10.1046/j.1365-201X.1996.211000.x
- Issue published online: 6 NOV 2003
- Article first published online: 6 NOV 2003
- Cited By
- fuzzy space;
- Na+ gradient;
- K+ pump;
- skeletal muscle;
Since intracellular Na+ activity (aiNa) is one important determinant of Na+, K+-pump rate as well as excitability and the finely tuned contractility, it is surprising that the relation between aiNa and pump rate reported by different authors has k0.5 varying between 10 and 40 mmol L-1. Other data also point to a variable relation between pump rate and aiNa. During stimulation of isolated rat soleus muscles at 2 Hz, ouabain-sensitive 86Rb uptake was increased in spite of the intracellular Na+ remaining unaltered. In isolated cardiomyocytes, a transient Na+, K+-pump current was observed upon activation by extracellular K+ in spite of good control of aiNa. Na+-loaded, isolated, sheep cardiac Purkinje fibres initially hyperpolarized over a period of up to 1 min upon activation of the Na+, K+ pump with no detectable change of aiNa. These examples are compatible with the existence of a micro-environment close to the membrane where diffusion is slower than in the rest of the cytosol, so that local aiNa may fluctuate or gradients may develop as visualized by Wendt-Gallitelli et al. (1993). We conclude that the reported relationships between Na+, K+-pump rate and aiNa in intact cells probably underestimate the true affinity of the Na+, K+ pump for Na+ due to a functional diffusion barrier beneath the sarcolemma, and also because of incomplete cell dialysis in whole-cell voltage clamp experiments. The Na+, K+ pump seems to be preferentially supplied with Na+ from the outside through neighbouring channels and transporters.