Rigor-force producing cross-bridges in skeletal muscle fibers activated by a substoichiometric amount of ATP.
Isometric skinned muscle fibers were activated by the photogeneration of a substoichiometric amount of ATP and their cross-bridge configurations examined during the development of the rigor force by x-ray diffraction and electron microscopy. By the photogeneration of approximately 100 microM ATP, approximately 2/3 of the concentration of the myosin heads in a muscle fiber, muscle fibers originally in the rigor state showed a transient drop of the force and then produced a long-lasting rigor force (approximately 50% of the maximal active force), which gradually recovered to the original force level with a time constant of approximately 4 s. Associated with the photoactivation, muscle fibers revealed small but distinct changes in the equatorial x-ray diffraction that run ahead of the development of force. After reaching a plateau of force, long-lasting intensity changes in the x-ray diffraction pattern developed in parallel with the force decline. Two-dimensional x-ray diffraction patterns and electron micrographs of the sectioned muscle fibers taken during the period of 1-1.9 s after the photoactivation were basically similar to those from rigor preparations but also contained features characteristic of fully activated fibers. In photoactivated muscle fibers, some cross-bridges bound photogenerated ATP and underwent an ATP hydrolysis cycle whereas a significant population of the cross-bridges remained attached to the thin actin filaments with no available ATP to bind. Analysis of the results obtained indicates that, during the ATP hydrolysis reaction, the cross-bridges detached from actin filaments and reattached either to the same original actin monomers or to neighboring actin monomers. The latter cross-bridges contribute to produce the rigor force by interacting with the actin filaments, first producing the active force and then being locked in a noncycling state(s), transforming their configuration on the actin filaments to stably sustain the produced force as a passive rigor force.
Yamada
Takenori
T
Department of Physiology, School of Medicine, Teikyo University, Tokyo 173-8605, Japan. yamada@rs.kagu.tus.ac.jp
Takezawa
Yasunori
Y
Iwamoto
Hiroyuki
H
Suzuki
Suechika
S
Wakabayashi
Katsuzo
K
D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000737:chemistry; D008027:Light; D008854:Microscopy, Electron; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000737:chemistry; D009127:Muscle Rigidity; D018482:Muscle, Skeletal / Q000473:pathology*; D009132:Muscles / Q000378:metabolism / Q000473:pathology; D011188:Potassium / Q000737:chemistry; D011817:Rabbits; D013314:Stress, Mechanical; D017356:Synchrotrons; D013997:Time Factors; D014961:X-Ray Diffraction
D000255:Adenosine Triphosphate; D011188:Potassium; D002118:Calcium