Comparative statistical mechanics of myosin molecular motors in rat heart, diaphragm and tracheal smooth muscle
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences. Pharmacy
Comptes rendus biologies / Institut de France. Académie des sciences. - Paris, 2002, currens
, p. 725-736
University of Antwerp
Purpose Statistical mechanics establishes a link between microscopic properties of matter and its bulk properties. A. Huxley's equations (1957)  provide the necessary phenomenological formalism to use statistical mechanics. Methods We compared statistical mechanics in rat diaphragm in tetanus (tet; n = 10) and twitch (tw; n = 12) modes, in heart in twitch mode (n = 20), and in tracheal smooth muscle in tetanus mode (TSM; n = 10). This powerful tool makes it possible to determine: (i) statistical entropy (S) which is related to the dispersal of energy and represents a measure of the degree of disorder in muscular system; (ii) thermodynamic force A/T (chemical affinity A and temperature T); (iii) thermodynamic flow (υ); (iv) entropy production rate (A/T × υ), which quantifies irreversible chemical processes generated by myosin crossbridge (CB) molecular motors. Results All muscles studied operated near equilibrium, i.e., A << 2500 J/mol and in a stationary linear regime, i.e., A/T varied linearly with υ. The heart operated farther from equilibrium than both diaphragm (tet and tw) and TSM, as attested by its high entropy production rate. S was of the same order of magnitude in heart and TSM but lower in diaphragm (tet and tw). Conclusion CB kinetics derived from A. Huxley's equations conferred a characteristic profile in terms of statistical mechanics on each muscle type. All studied muscles differed in terms of statistical entropy, chemical affinity, and entropy production rate. Stimulation mode (tet and tw) modulated CB kinetics and statistical mechanics. All muscle types operated near equilibrium and in a stationary linear regime.