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

Abstract

Norris SM, Bombardier E, Smith IC, Vigna C, Tupling AR. ATP consumption by sarcoplasmic reticulum Ca 2ϩ pumps accounts for 50% of resting metabolic rate in mouse fast and slow twitch skeletal muscle. Am J Physiol Cell Physiol 298: C521-C529, 2010. First published December 16, 2009; doi:10.1152/ajpcell.00479.2009In this study, we aimed to directly quantify the relative contribution of Ca 2ϩ 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 (V O2, l·g wet wt) measured polarographically at 30°C was ϳ25% higher in soleus (0.61 Ϯ .03) than in EDL (0.46 Ϯ .03). To quantify the specific contribution of Ca 2ϩ cycling to resting metabolic rate, cyclopiazonic acid (CPA), a highly specific inhibitor of sarco(endo)plasmic reticulum Ca 2ϩ ATPases (SERCAs), was added to the bath at different concentrations (1, 5, 10, and 15 M). There was a concentration-dependent effect of CPA on V O2, with increasing CPA concentrations up to 10 M resulting in progressively greater reductions in muscle V O2. There were no differences between 10 and 15 M CPA, indicating that 10 M CPA induces maximal inhibition of SERCAs in isolated muscle preparations. Relative reduction in muscle V O2 in response to CPA was nearly identical in EDL (1 M, 10.6 Ϯ 3.0%; 5 M, 33.2 Ϯ 3.4%; 10 M, 49.2 Ϯ 2.9%; 15 M, 50.9 Ϯ 2.1%) and soleus (1 M, 11.2 Ϯ 1.5%; 5 M, 37.7 Ϯ 2.4%; 10 M, 50.0 Ϯ 1.3%; 15 M, 49.9 Ϯ 1.6%). The results indicate that ATP consumption by SERCAs is responsible for ϳ50% 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. oxygen consumption; in vitro; isolated skeletal muscle; energy expenditure; calcium pump SKELETAL MUSCLE REPRESENTS ϳ40% of body weight and accounts for ϳ20 -30% of whole body basal metabolic rate (45, 60). Like other cell types, a portion of basal metabolic rate in skeletal muscle can be attributed to the cycling of Ca 2ϩ across cell membranes, but very few studies have attempted to quantify the relative contribution of Ca 2ϩ cycling to resting muscle metabolism. Under basal conditions in skeletal muscle, sarco-(endo)plasmic reticulum Ca 2ϩ -ATPases (SERCAs) are responsible for maintaining a Ͼ10 4 -fold Ca 2ϩ concentration gradient across the sarcoplasmic reticulum (SR) membrane and for keeping the cytosolic free Ca 2ϩ concentration ([Ca 2ϩ ] f ) at or below 100 nM (53). Under optimized states, SERCAs transport 2 mol of Ca 2ϩ across the SR membrane upon the hydrolysis of 1 mol of ATP (15,31, 51). Early estimates of the energy consumed by SERCAs in muscle under basal conditions were based on measurements of the rate of Ca 2ϩ efflux from isolated SR vesicles and then the amount of ATP that would be required to reuptake that Ca 2ϩ was calculated assuming an optimal Ca 2ϩ -to-ATP coupling ratio. This appr...

Effects of Catecholamine Stress on Diastolic Function and Myocardial Energetics in Obesity

“…The association between reduced myocardial energetics and diastolic dysfunction has been shown in multiple studies. 7,24 This is in line with the concept that an impairment in high-energy phosphate metabolism initially affects the ability of the sarcoplasmic reticular Ca 2ϩ ATPase (SERCA), the most energetically demanding of all enzymes involved in contractile function, 25 to lower cytosolic Ca 2ϩ and thus impairs diastolic function. So far, the vast majority of data supporting an impairment in myocardial energetics in obesity come from animal models, 12,26 with only 1 prior study showing reduced resting myocardial energetics in human male obesity.…”

“…In contrast, in the obese cohort, there was no correlation between the increase in heart rate and the increase in diastolic filling rate (RϭϪ0. 25,Pϭ0.28). This loss of the correlation between heart rate and diastolic function in obesity has not been described before.…”

Mitochondrial and sarcoplasmic reticulum abnormalities in cancer cachexia: Altered energetic efficiency?

“…In fact, upregulation of SERCA1 in skeletal muscle has been described in disuse atrophy [31]. It is also very interesting to remark that ATP consumption by SERCA pumps accounts for 50% of resting metabolic rate in mice [32]. If we take into consideration the fact that cancer patients have an increased energy expenditure [33], which contributes to weight loss, it becomes clear the importance that SERCA pumps may have in cancer cachexia.…”

Influences of temperature, oxidative stress, and phosphorylation on binding of heat shock proteins in skeletal muscle fibers

“…HSP72, in contrast, appears to bind in stress situations primarily to membrane proteins, and in particular has been found to bind to and stabilize the structure and function of the sarco(endo)plasmic reticulum Ca 2ϩ -ATPase pump (SERCA1a and SERCA2a) in skeletal and cardiac muscle following heat stress (13,45). In apparent accord, we have recently reported that the absolute amounts of HSP72 in skeletal muscles are much lower than the density of SERCA pumps [HSP72 content ϳ1.1 and 4.6 mol/kg wet weight in rat extensor digitorum longus (EDL) and SOL muscle (21), and total SERCA content ϳ100 and ϳ20 -35 mol/kg, respectively (34,49)], that heat treatment of skeletal muscles to 45°C causes tight binding of Ͼ95% of the HSP72 present, and that exposure of such heat-treated fibers to Triton X-100 for 10 min caused diffusional loss of a similar proportion (ϳ50% to 70%) of both the HSP72 and the SERCA (21).…”

“…In this case the HSP72 evidently recognized and bound to targets within the fibers because of alterations in target proteins rather than alterations in the HSP72 itself. It is likely that SERCA is the predominant binding site of the HSP72 in the skinned fibers here, given 1) the propensity of SERCA to bind HSP72 (13,14,45), 2) the comparatively high absolute number of SERCA proteins present in muscle fibers [ϳ100 and 20 -35 mol/kg wet weight in EDL and SOL muscle, respectively (34,49)], and 3) the relatively greater additional HSP72 binding occurring in the EDL fibers compared with SOL fibers (Fig. 6) [see also INTRODUCTION and Ref.…”