Activation of electrogenic sodium pump in mammalian skeletal muscle by external cations.
The effect of change of the external ionic composition on "Na-loaded" and "K-depleted" soleus muscle fibres of K-deficient rats was investigated by recording resting membrane potentials. The addition of K, Rb, Cs and NH4 ions to K-free Krebs solution bathing "Na-rich" muscles resulted in a rapid hyperpolarization. The hyperpolarization was abolished by removing the above cations, cooling to ca. 4 degrees C, and adding 0.1 mM ouabain. The effectiveness of cations for activating the electrogenic Na pump was Rb greater than or equal to K greater than NH4 greater than Cs, and NH4 ions seemed to be unique in their stimulating action. The resting cell membrane of "Na-rich" muscles is permeable to cations in the order of Rb = K greater than Cs greater than NH4. Reducing Na ions in Krebs solution had no effect on the rate of Na-pumping in "Na-rich" muscle fibres at a given K concentration. It is concluded that the external K ions could be replaced by Rb, Cs and NH4 ions in activating the electrogenic Na pump in "Na-rich" soleus muscle fibres, but that the electrogenic Na pump in this tissue does not require the external Na ions.
D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002463:Cell Membrane Permeability; D002586:Cesium / Q000494:pharmacology; D003080:Cold Temperature; D006614:Hindlimb; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011191:Potassium Deficiency / Q000503:physiopathology; D051381:Rats; D012413:Rubidium / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D002586:Cesium; D010042:Ouabain; D000641:Ammonia; D012964:Sodium; D012413:Rubidium; D011188:Potassium