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1. Active transport of Na⁺ and K⁺ by Na-rich extensor digitorum and soleus muscles of rat was found to be increased considerably when muscles were innervated during enrichment with Na⁺ in K-free modified Krebs solution containing 160 mM-Na at 2° C and recovery in a similar fluid with 10 mM-K and 137 mM-Na at 37° C, bubbled with oxygen.

2. Addition of acetylcholine (2·0 µg/ml.) to recovery fluid containing denervated extensors increased active transport, whereas addition of eserine (50 µg/ml.), decamethonium (0·1 µg/ml.) and to a lesser extent tubocurarine (0·26 µg/ml.) inhibited active transport. Blocking of nerve conduction in innervated extensor inhibited K⁺ uptake more than Na⁺ excretion.

3. The membrane potential of Na-rich extensor muscles measured soon after re-immersion in recovery fluid was higher in denervated than in innervated muscles. In the latter it was close to the K-equilibrium potential (E_K). It is suggested that denervation here makes the Na-pump electrogenic by decreasing K⁺ uptake either by decreased permeability or by inactivating a K-pump. Evidence is presented that the latter is more likely.

4. Addition of isoprenaline to Na-rich soleus muscles in recovery fluid increased active transport and reduced the membrane potential measured soon after re-immersion in recovery fluid. The Na-pump still remained electrogenic in the presence of isoprenaline. It was suggested that isoprenaline might also stimulate the Na-pump, perhaps through activation of lactic dehydrogenase.

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				T. CLAUSEN Na+-K+ Pump Regulation and Skeletal Muscle Contractility Physiol Rev, October 1, 2003; 83(4): 1269 - 1324. [Abstract] [Full Text] [PDF]