title: Efficiency of work performance and contraction velocity in isotonic tetani of frog sartorius.
abstract: Mechanical work, ATP, ADP, PC, free creatine and lactate concentrations were determined on IAA poisoned frog sartorii tetanically stimulated in humidified N2 at 10 degrees C in isotonic conditions (0.25 or 0.45 Po). Tetanus duration was 0.35 s, number of tetani was varied from 0 (rest) to 25 (exhaustion). The mechanical work performed per mole ATP + PC split (W*P) amounted on the average to 16.7 kJ/mol. It was observed, however, that W*P increased from about 13 to about 24 kJ/mol with decreasing ATP concentration from about 2 (resting value) to about 1 mumol/g and that this decrease in ATP was associated with a decrease of the shortening (and relaxation) speed of the muscle to about 30% of the values observed on the first tetanus. It is concluded that the thermodynamic efficiency of muscle contraction, calculated from the ratio of WP* (measured) to the thermodynamic affinity (free energy change) of ATP hydrolysis (estimated) increases from about 0.3 to about 0.5 with decreasing ATP concentration and shortening speed.
authors.affiliation: Department of Physiology, Centre Médical Universitaire, Geneva, Switzerland.
authors.forename: P E
authors.initials: PE
authors.lastname: di Prampero
authors.forename: U
authors.initials: U
authors.lastname: Boutellier
authors.forename: A
authors.initials: A
authors.lastname: Marguerat
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D066298:In Vitro Techniques; D007461:Iodoacetates / Q000494:pharmacology; D019807:Iodoacetic Acid; D007551:Isotonic Contraction; D009119:Muscle Contraction; D009132:Muscles / Q000032:analysis / Q000378:metabolism / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism; D005082:Physical Exertion; D011895:Rana ridibunda; D013997:Time Factors
chemical_list: D007461:Iodoacetates; D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D019807:Iodoacetic Acid