Effects of K+, Mg2+ deficiency and adrenal steroids on Na+, K(+)-pump concentration in skeletal muscle.
Animal studies have shown that deficiency of K+ is associated with a reduction in the concentration of Na+, K+ pumps in skeletal muscle, and that this reduction is closely correlated with the reduction in the muscle K+ concentration. Furthermore, animals deficient in Mg+ show a downregulation of the Na+, K(+)-pump concentration, but this seems to be secondary to the concomitant K+ deficiency, which often accompanies Mg2+ deficiency. Measurements on skeletal muscle biopsies from patients who had been in long-term treatment with diuretics showed that 55% had reduced concentrations of both K+ and Mg2+, and that this was associated with a reduction in the concentration of Na+, K+ pumps. Furthermore, the Na+, K(+)-pump concentration correlated significantly with both muscle K+ and Mg2+, suggesting that the downregulation of the Na+, K+ pumps was related to the loss of K+, as predicted from the animal experiments. In accordance with this, normalization of muscle K+ and Mg2+ in response to oral Mg2+ supplementation, resulted in a restoration of the Na+, K+ pumps. Apart from thyroid hormone, which is another major regulator for the Na+, K(+)-pump concentration, other hormones may be of importance. It is well known that adrenal steroids control the synthesis of Na+, K+ pumps in the kidney and heart. Recently, treatment with dexamethasone was found to increase the Na+, K(+)-pump concentration in rat skeletal muscle. The increase was found in EDL, soleus, gastrocnemius and diaphragm muscles, and amounted to 23-52%. In contrast, treatment with aldosterone induced a decrease in the Na+, K(+)-pump concentration, which was closely correlated to the reduced K+ content of the muscles. The results indicate that in skeletal muscle, high doses of glucocorticoids upregulate the concentration of Na+, K+ pumps, whereas mineralocorticoids induce a downregulation which is secondary to the concomitant K+ deficiency.
Dørup
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Institute of Physiology, University of Aarbus, Denmark.
D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000818:Animals; D006801:Humans; D008275:Magnesium Deficiency / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011191:Potassium Deficiency / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*
D000305:Adrenal Cortex Hormones; D000254:Sodium-Potassium-Exchanging ATPase