TY - JOUR
T1 - Interference fine structure and sarcomere length dependence of the axial x-ray pattern from active single muscle fibers
AU - Linari, M
AU - Piazzesi, G
AU - Dobbie, I
AU - Koubassova, N
AU - Reconditi, M
AU - Narayanan, T
AU - Diat, O
AU - Irving, M
AU - Lombardi, V
PY - 2000/6/20
Y1 - 2000/6/20
N2 - Axial x-ray diffraction patterns from single intact fibers of frog skeletal muscle were recorded by using a highly collimated x-ray beam at the European Synchrotron Radiation Facility. During isometric contraction at sarcomere lengths 2.2-3.2 mu m, the M3 x-ray reflection, associated with the repeat of myosin heads along the filaments, was resolved into two peaks. The total M3 intensity decreased linearly with increasing sarcomere length and was directly proportional to the degree of overlap between myosin and actin filaments, showing that it comes from myosin heads in the overlap region. The separation between the M3 peaks was smaller at longer sarcomere length and was quantitatively explained by x-ray interference between myosin heads in the two overlap regions of each sarcomere. The relative intensity of the M3 peaks was independent of sarcomere length, showing that the axial periodicities of the nonoverlap and overlap regions of the myosin filament have the same value, 14.57 nm, during active contraction. In resting fibers the periodicity is 14.34 nm, so muscle activation produces a change in myosin filament structure in the nonoverlap as well as the overlap part of the filament. The results establish x-ray interferometry as a new tool for studying the motions of myosin heads during muscle contraction with unprecedented spatial resolution.
AB - Axial x-ray diffraction patterns from single intact fibers of frog skeletal muscle were recorded by using a highly collimated x-ray beam at the European Synchrotron Radiation Facility. During isometric contraction at sarcomere lengths 2.2-3.2 mu m, the M3 x-ray reflection, associated with the repeat of myosin heads along the filaments, was resolved into two peaks. The total M3 intensity decreased linearly with increasing sarcomere length and was directly proportional to the degree of overlap between myosin and actin filaments, showing that it comes from myosin heads in the overlap region. The separation between the M3 peaks was smaller at longer sarcomere length and was quantitatively explained by x-ray interference between myosin heads in the two overlap regions of each sarcomere. The relative intensity of the M3 peaks was independent of sarcomere length, showing that the axial periodicities of the nonoverlap and overlap regions of the myosin filament have the same value, 14.57 nm, during active contraction. In resting fibers the periodicity is 14.34 nm, so muscle activation produces a change in myosin filament structure in the nonoverlap as well as the overlap part of the filament. The results establish x-ray interferometry as a new tool for studying the motions of myosin heads during muscle contraction with unprecedented spatial resolution.
UR - http://www.scopus.com/inward/record.url?scp=0034691199&partnerID=8YFLogxK
U2 - 10.1073/pnas.97.13.7226
DO - 10.1073/pnas.97.13.7226
M3 - Article
SN - 1091-6490
VL - 97
SP - 7226
EP - 7231
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 13
ER -