Effects of Electrical Stimulation and Insulin on Na + –K + ‐ATPase ([ 3 H]Ouabain Binding) in Rat Skeletal Muscle

Exercise has been reported to increase the Na + –K + ‐ATPase (Na + –K + pump) α 2 isoform in the plasma membrane 1.2‐ to 1.9‐fold, purportedly reflecting Na + –K + pump translocation from an undefined intracellular pool. We examined whether Na + –K + pump stimulation, elicited by muscle contraction or insulin, increases the plasma membrane Na + –K + pump content ([ 3 H]ouabain binding) in muscles from young rats. Stimulation of isolated soleus muscle for 10 s at 120 Hz caused a rapid rise in intracellular Na + content, followed by an 18‐fold increase in the Na + re‐extrusion rate (80 % of theoretical maximum). Muscles frozen immediately or 120 s after 10–120 s stimulation showed 10–22 % decrease in [ 3 H]ouabain binding expressed per gram wet weight, but with no significant change expressed per gram dry weight. In soleus muscles from adult rats, [ 3 H]ouabain binding was unaltered after 10 s stimulation at 120 Hz. Extensor digitorum longus (EDL) muscles stimulated for 10–60 s at 120 Hz showed no significant change in [ 3 H]ouabain binding. Insulin (100 mU ml −1 ) decreased intracellular Na + content by 27 % and increased 86 Rb uptake by 23 % soleus muscles, but [ 3 H]ouabain binding was unchanged. After stimulation for 30 s at 60 Hz soleus muscle showed a 30% decrease in intracellular Na + content, demonstrating increased Na + –K + pump activity, but [ 3 H]ouabain binding measured 5 to 120 min after stimulation was unchanged. Stimulation of soleus or EDL muscles for 120–240 min at 1 Hz (continuously) or 10 Hz (intermittently) produced no change in [ 3 H]ouabain binding per gram dry weight. In conclusion, the stimulating effects of electrical stimulation or insulin on active Na + , K + ‐transport in rat skeletal muscle could not be even partially accounted for by an acute increase in the content of functional Na + –K + pumps in the plasma membrane.