ATP consumption by sarcoplasmic reticulum Ca2+pumps accounts for 50% of resting metabolic rate in mouse fast and slow twitch skeletal muscle

Abstract

In this study, we aimed to directly quantify the relative contribution of Ca2+cycling to resting metabolic rate in mouse fast-twitch (extensor digitorum longus, EDL) and slow-twitch (soleus) skeletal muscle. Resting oxygen consumption of isolated muscles (V̇o2, μl·g wet wt−1·s−1) measured polarographically at 30°C was ∼25% higher in soleus (0.61 ± .03) than in EDL (0.46 ± .03). To quantify the specific contribution of Ca2+cycling to resting metabolic rate, cyclopiazonic acid (CPA), a highly specific inhibitor of sarco(endo)plasmic reticulum Ca2+ATPases (SERCAs), was added to the bath at different concentrations (1, 5, 10, and 15 μM). There was a concentration-dependent effect of CPA on V̇o2, with increasing CPA concentrations up to 10 μM resulting in progressively greater reductions in muscle V̇o2. There were no differences between 10 and 15 μM CPA, indicating that 10 μM CPA induces maximal inhibition of SERCAs in isolated muscle preparations. Relative reduction in muscle V̇o2in response to CPA was nearly identical in EDL (1 μM, 10.6 ± 3.0%; 5 μM, 33.2 ± 3.4%; 10 μM, 49.2 ± 2.9%; 15 μM, 50.9 ± 2.1%) and soleus (1 μM, 11.2 ± 1.5%; 5 μM, 37.7 ± 2.4%; 10 μM, 50.0 ± 1.3%; 15 μM, 49.9 ± 1.6%). The results indicate that ATP consumption by SERCAs is responsible for ∼50% of resting metabolic rate in both mouse fast- and slow-twitch muscles at 30°C. Thus SERCA pumps in skeletal muscle could represent an important control point for energy balance regulation and a potential target for metabolic alterations to oppose obesity.