Weakly attached cross-bridges in relaxed frog muscle fibers.
Tension responses due to small, rapid length changes (completed within 40 microseconds) were obtained from skinned single frog muscle fiber segments (4-10 mm length) incubated in relaxing and rigor solutions at various ionic strengths. The first 2 ms of these responses can be described with a linear model in which the fiber is regarded as a rod, composed of infinitesimally small, identical segments, containing one undamped elastic element and two or three damped elastic elements and a mass in series. Rigor stiffness changed less than 10% in a limited range, 40-160 mM, of ionic strength conditions. Equatorial x-ray diffraction patterns show a similar finding for the filament spacing and intensity ratio I(11)/I(10). Relaxed fibers became stiffer under low ionic strength conditions. This stiffness increment can be correlated with a decreasing filament spacing and (an increased number of) weakly attached cross-bridges. Under low ionic strength conditions an additional recovery (1 ms time constant) became noticeable which might reflect characteristics of weakly attached cross-bridges.
Jung
D W
DW
Department of Physiology, University of Amsterdam, The Netherlands.
Blangé
T
T
de Graaf
H
H
Treijtel
B W
BW
D000199:Actins / Q000502:physiology; D000818:Animals; D004548:Elasticity; D066298:In Vitro Techniques; D008962:Models, Theoretical; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009132:Muscles / Q000502:physiology*; D011893:Rana esculenta; D014961:X-Ray Diffraction
D000199:Actins