ATP Consumption and Efficiency of Human Single Muscle Fibers with Different Myosin Isoform Composition

Abstract

Chemomechanical transduction was studied in single fibers isolated from human skeletal muscle containing different myosin isoforms. Permeabilized fibers were activated by laser-pulse photolytic release of 1.5 mM ATP from p(3)-1-(2-nitrophenyl)ethylester of ATP. The ATP hydrolysis rate in the muscle fibers was determined with a fluorescently labeled phosphate-binding protein. The effects of varying load and shortening velocity during contraction were investigated. The myosin isoform composition was determined in each fiber by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. At 12 degrees C large variations (three- to fourfold) were found between slow and fast (2A and 2A-2B) fibers in their maximum shortening velocity, peak power output, velocity at which peak power is produced, isometric ATPase activity, and tension cost. Isometric tension was similar in all fiber groups. The ATP consumption rate increased during shortening in proportion to shortening velocity. At 12 degrees C the maximum efficiency was similar (0.21-0.27) for all fiber types and was reached at a higher speed of shortening for the faster fibers. In all fibers, peak efficiency increased to approximately 0.4 when the temperature was raised from 12 degrees C to 20 degrees C. The results were simulated with a kinetic scheme describing the ATPase cycle, in which the rate constant controlling ADP release is sensitive to the load on the muscle. The main difference between slow and fast fibers was reproduced by increasing the rate constant for the hydrolysis step, which was rate limiting at low loads. Simulation of the effect of increasing temperature required an increase in the force per cross-bridge and an acceleration of the rate constants in the reaction pathway.

Skinned fibres produce the same power and force as intact fibre bundles from muscle of wild rabbits

“…For example, the maximum specific isometric force reported for human Type 2A fibres at 12°C ranges from 22 to 250 kPa (Harridge et al, 1996;Larsson et al, 1997; see also Kalakoutis et al, 2014). Similarly, for this fibre type and temperature, the maximum power output ranges from 1.6 to 7.3 W l −1 He et al, 2000). Thus, for both force and power, the indications are that the details of the methods used in a particular laboratory have a strong influence on the quantitative results.…”

Critical determinants of combined sprint and endurance performance: an integrative analysis from muscle fiber to the human body

“…Maximal efficiency of type I and type IIA fibers is similar (70); however, type I fibers attain their peak efficiency at lower shortening velocities (70). Accordingly, it has been suggested that a large proportion of slow-type fibers results in a higher efficiency at common cycling cadences [i.e., 602120 rpm (1)].…”

Exergy Analysis of the Musculoskeletal System Efficiency during Aerobic and Anaerobic Activities

“…Based on the results of [46], there is even an efficiency for human muscle cells for some restricted conditions. For an isolated muscle, the efficiency ranges from 0.14 to 0.28 (environment of 12 to 20 • C).…”