title: Decrease in stiffness during shortening in calcium activated skinned muscle fibers.
abstract: Single fibers from frog sartorius or semitendinosus muscle were mechanically skinned and activated in ATP salt solution containing 10 micro M Ca2+ (7 degrees C). After development of an isometric contraction, fibers were released at constant speed (0.03-2.4 s-1). During ramp shortening, stiffness was determined from the slope of the tension-length diagram obtained during superimposed quick stretches. Both force and stiffness decreased, as the ramp shortening proceeded and approached a steady value after about 60 ms. An increase in speed of shortening caused a decrease in fiber tension and stiffness and an increase in the ratio of stiffness to tension, suggesting a decrease in both the number of attached crossbridges and in the average force per crossbridge.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004548:Elasticity; D006706:Homeostasis; D009119:Muscle Contraction / Q000187:drug effects*; D011892:Rana catesbeiana; D011896:Rana temporaria; D013997:Time Factors
chemical_list: D002118:Calcium