Temperature dependence of the axial motions of myosin heads during isometric contraction in single fibres from frog muscle

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University of Central Lancashire / University of Liverpool (2002) J Physiol 543P, S118

Communications: Temperature dependence of the axial motions of myosin heads during isometric contraction in single fibres from frog muscle

M. Reconditi*, G. Piazzesi*, M. Linari*, L. Lucii*, Y.-B. Sun†, P. Boesecke‡, T. Narayanan‡, V. Lombardi* and M. Irving†

*Department of Physiology, University of Florence, I-50134 Firenze, Italy, †School of Biomedical Sciences, King's College London, London SE1 1UL, UK and ‡ESRF, BP 220, 38043 Grenoble, France

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Skeletal muscle fibres generally produce higher active isometric force at higher temperature. In intact fibres from frog skeletal muscle this is due to a higher force per myosin cross-bridge rather than an increase in the number of cross-bridges (Linari et al. 2001). We investigated the structural basis of the temperature effect by X-ray diffraction at beamline ID2 of the European Synchrotron Radiation Facility (ESRF), Grenoble, France, using single fibres from anterior tibialis muscle of frogs (Rana temporaria) that had been humanely killed. The sarcomere length was 2.1 mm. Isometric tetanic force was 34 ± 5 % (mean ± S.D., n = 5 fibres) greater at 11°C than at 0°C. There was no change in the intensity of the first actin layer line, which is sensitive to the number of myosin heads attached to actin. The intensity of the M3 X-ray reflection from the axial repeat of the myosin heads along the filaments was 11 ± 1 % (mean ± S.D.) greater at the higher temperature. The fine structure of the M3 reflection, arising from interference between the two arrays of myosin heads in each myosin filament, was used to measure the axial position of the heads with respect to the centre of the filament (Linari et al. 2000). During an isometric tetanus the M3 reflection was composed of two well-resolved peaks. The ratio of the intensity of the higher angle peak to that of the lower angle peak was 0.88 ± 0.10 at 0 °C and 0.69 ± 0.09 at 11 °C. This difference corresponds to an average shift of the centres of mass of the myosin heads towards the centre of the filament by 0.31 nm at the higher temperature. The changes in intensity and interference fine structure of the M3 reflection were analysed using a structural model for the myosin filament incorporating filament compliance and an atomic model for the myosin head in which force is generated by tilting of its light chain domain with respect to the catalytic domain (Rayment et al. 1993; Piazzesi et al. 2002). The results show that the observed increase in force per myosin head with increasing temperature can be explained by the tilting-light chain domain model.

This work was supported by MRC (UK), MURST and Telethon (Italy), EU, EMBL and ESRF.

All procedures accord with current National guidelines.

Where applicable, experiments conform with Society ethical requirements.

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