X-Ray Diffraction Study of the Effect of Temperature on the Structure of Mammalian Muscle at Rest and During Isometric Contraction

Abstract

X-ray diffraction patterns were recorded from whole EDL muscle of 1-2 month old mice at rest and during isometric contraction (force T0) at temperatures between 10 and 35°C. Muscles were vertically mounted at the BioCAT beamline (APS, Argonne, USA, X-ray energy 12 keV, camera length 3.5m) in a trough containing physiological solution gassed with carbogen (95% O2 plus 5% CO2, pH=7.4) and at the in situ rest length. X-ray exposure time was 20 ms for both rest and T0, repeated twice at each temperature. The muscle was shifted axially between exposures to minimise radiation damage. T0 was 251±17 kPa(mean±S.E.M., n=3) at 30°C (T0,30) and not significantly different at 35°C. Below 30°C force decreased with decreasing temperature, reaching 0.25 T0,30 at 10°C. The M3 meridional reflection from the axial repeat of the myosin heads was sampled by X-ray interference between the two halves of the myosin filament. At rest the M3 reflection consisted of a main peak with two small satellite peaks; during activation it consisted of two main peaks with an intensity ratio (RM3; high angle/low angle) that varied from ∼0.8 at 30°C to ∼1.1 at 10°C. The total M3 intensity (IM3) was five times smaller at 10 than at 30°C, both at rest and during isometric contraction. The M3 spacing (SM3) increased by ∼1.3% from rest to isometric contraction at all temperatures; the spacing of its second order (SM6) had a markedly different temperature dependence at rest, but a roughly similar temperature dependence during isometric contraction, so that, from rest to T0, SM6 increased by ∼1.3% at 30°C but by only ∼0.5% at 10°C.Supported by Ente Cassa di Risparmio di Firenze, MIUR, CNISM, (Italy), MRC (U.K.), NIH.