Active transport of sodium and potassium in mammalian skeletal muscle and its modification by nerve and by cholinergic and adrenergic agents

Abstract

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 m[image]-Na at 2[degree]C and recovery in a similar fluid with 10 m[image].-K and 137 m[image]-Na at 37[degree]C, bubbled with oxygen. Addition of acetylcholine (2.0 [mu]g7ml) to recovery fluid containing denervated extensors increased active transport, whereas addition of eserine (50 /[mu]g/ml), decamethonium (0.1 [mu]g/ ml) and to a lesser extent tubocurarine (0.2 [mu]g/ml) inhibited active transport Blocking of nerve conduction in innervated extensor inhibited K+ uptake more than Na+ excretion. 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 (Ek). It is suggested that denervation here makes the Na-pump electrogenic by decreasing K uptake either by decreased permeability or by in-activation a K-pump. Evidence is presented that the latter is more likely. 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.