Cross bridges account for only 20 % of total ATP consumption during submaximal isometric contraction in mouse fast-twitch skeletal muscle

only 20 % of total ATP consumption during submaximal isometric contraction in mouse fast-twitch skeletal muscle. Am J Physiol Cell Physiol 291: C147–C154, 2006. First published February 15, 2006; doi:10.1152/ajpcell.00578.2005.—It is generally believed that cross bridges account for 50 % of the total ATP consumed by skeletal muscle during contraction. We investigated the effect of N-benzyl-p-toluene sulfonamide (BTS), an inhibitor of myosin ATPase, on muscle force production and energy metabolism under near-physio-logical conditions (50-Hz stimulation frequency at 30°C results in 35 % of maximal force). Extensor digitorum longus muscles from mice were isolated and stimulated to perform continuous isometric tetanic contractions. Metabolites of energy metabolism were analyzed with fluorometric techniques. ATP turnover was estimated from the changes in phosphocreatine (PCr), ATP, and lactate (2ATP PCr [1.5lactate]). During contractions (2–10 s), BTS decreased force production to 5 % of control. Under these conditions, BTS inhibited ATP turnover by only 18–25%. ATP turnover decreased markedly and similarly with and without BTS as the duration of contraction progressed. In conclusion, cross bridges (i.e., actomyosin ATPase) account for only a small fraction (20%) of the ATP consumption during contraction in mouse fast-twitch skeletal muscle under near-physiological conditions, suggesting that ion pumping is the major energy-consuming process. ATPase; high-energy phosphates; lactate DURING MUSCLE CONTRACTION, 50–80 % of the total ATP con-sumption is thought to be accounted for by actomyosin ATP-ase, with the remainder accounted for by ion pumping (1, 7, 12