IJCsatellite IJCsatellite/JTB


Journal of Theoretical Biology

Volume 235, Issue 3 , 7 August 2005, Pages 381-392


Statistical mechanics of myosin molecular motors in skeletal muscles

Y. Lecarpentiera, d, , , F.-X. Blancb, J. Quillardc, J.-L. H?berta, X. Krokidisa and C. Coiraultd

aService de Physiologie, H?pital de Bic?tre, Assistance Publique-H?pitaux de Paris, Le Kremlin-Bic?tre, France
bServices de M?decine Interne, H?pital de Bic?tre, Assistance Publique-H?pitaux de Paris, Le Kremlin-Bic?tre, France
cService d’ Anatomo-Pathologie, H?pital de Bic?tre, Assistance Publique-H?pitaux de Paris, Le Kremlin-Bic?tre, France
dInserm U572, H?pital Lariboisi?re, Paris, France

Received 13 October 2004; revised 7 January 2005; accepted 25 January 2005. Communicated by Athelstan Cornish-Bowden. Available online 19 March 2005.

Statistical mechanics provides the link between microscopic properties of matter and its bulk properties. The grand canonical ensemble formalism was applied to contracting rat skeletal muscles, the soleus (SOL, n=30) and the extensor digitalis longus (EDL, n=30). Huxley's equations were used to calculate force (π) per single crossbridge (CB), probabilities of six steps of the CB cycle, and peak muscle efficiency (Effmax). SOL and EDL were shown to be in near-equilibrium (CB cycle affinity ) and stationary state (linearity between CB cycle affinity and myosin ATPase rate). The molecular partition function (z) was higher in EDL (1.126±0.005) than in SOL (1.050±0.003). Both π and Effmax were lower in EDL (8.3±0.1 pN and 38.1±0.2%, respectively) than in SOL (9.2±0.1 pN and 42.3±0.2%, respectively). The most populated step of the CB cycle was the last detached state (D3) (probability PD3: 0.890±0.004 in EDL and 0.953±0.002 in SOL). In each muscle group, both π and Effmax linearly decreased with z and statistical entropy and increased with PD3. We concluded that statistical mechanics and Huxley's formalism provided a powerful combination for establishing an analytical link between chemomechanical properties of CBs, molecular partition function and statistical entropy.

Keywords: Statistical entropy; Canonical ensembles; Partition functions

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