Force response to width and length perturbations in compressed skinned skeletal muscle fibers.
Previous studies have shown that radial compression of calcium-activated skinned skeletal muscle fibers, with attendant reduction of filament lattice spacing, reduces isometric force generation. In relaxed skinned fibers, radial compression produces a marked increase in axial elastic modulus, and the response to a small amplitude length perturbation resembles that of a muscle in rigor. We interpret these results as indicating that radial compression of the myofilament lattice produces "hindered" cross-bridges which are load bearing but not force generating. The experiments reported here were designed to study the effect(s) of "hindered" cross-bridges on both the time course of isometric force responses following Ca2+ activation and fiber width and length perturbations. The experiments were carried out at room temperature on radially compressed skinned single rabbit soleus fibers. Force development following step-wise Ca2+ activation and step-wise changes of fiber width was "slow" (60-90 sec) compared to that in normal width fibers (approximately 1 sec), and could be approximated by a single exponential curve. Force redevelopment following a length release in compressed fibers was both more rapid and more complicated than force development following activation and width steps, and required a double exponential curve for an adequate description. The results are consistent with the notion that hindered cross-bridges form as a result of lattice compression, and that the hindered bridges affect the force responses following width and length perturbations.
D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004548:Elasticity; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits; D013997:Time Factors
D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D002118:Calcium