Energetics of active sodium-potassium transport following stimulation with insulin, adrenaline or salbutamol in rat soleus muscle

Abstract

The total metabolic energy expenditure associated with active Na−K-transport over the first 20 min of stimulation with insulin, adrenaline or salbutamol (ΔH_mNa−K) was determined from direct calorimetric and tracer ion flux measurements in isolated muscles at rest. The reversible work performed by the Na−K-pump during the same interval of time (W_revNa−K) was calculated as the product of the ouabain-suppressible Na−K transfers and the mean free energy increase imparted to the two ions as they are transported against their electrochemical gradients across the plasma membrane. Comparison of membrane potential and intracellular Na and K concentrations before and after the stimulations indicated that part of W_revNa−K had contributed to increase the ion electrochemical gradients in the preparation (i.e. had not been lost as heat) during the 20 min period. Accordingly, the maximum value of ΔH_mNa−K was taken as the sum of the ouabain-suppressible heat production and W_revNa−K. Following stimulation with insulin, adrenaline or salbutamol this maximum corresponded to 10, 10 and 12% respectively, of basal metabolism. Under the same three conditions, the minimum “energetic efficiency” of the active Na−K-transport process, defined as the ratio between W_revNa−K and maximum ΔH_mNa−K, was 35, 41 and 38%, respectively.