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1 Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
* To whom correspondence should be addressed. E-mail: abram.katz{at}fyfa.ki.se.
It is generally believed that cross-bridges account for more than 50% of the total ATP consumed by skeletal muscle during contraction. We investigated the effect of N-benzyl-p-toluene sulphonamide (BTS), an inhibitor of myosin ATPase, on muscle force production and energy metabolism under near physiological conditions (50 Hz stimulation frequency; 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 (-2
ATP - 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 (ie, 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.
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