ABSTRACT
The properties of some models of the actin filament are compared with those of the thin filament in muscle. The greater stiffness of thin filaments ex vivo with respect to F-actin in vitro is attributed to the effect of both protein osmotic pressure and the attached cross-bridges. By comparing the stiffness of thin filaments in vitro and in isometric and rigor muscles the stiffness of thin filaments in relaxed muscle is computed. The upper limit of thin filament stretching is deduced to approach approximately 10 nm microm(-1). It is also calculated that, on stretching by 2.02 nm of the fully non-overlapped thin filament or by 1.59 nm of the thin filament on isometric contraction, the energy released on the hydrolysis of one molecule of ATP is fully used up.
Subject(s)
Actin Cytoskeleton/physiology , Actins/chemistry , Muscles/physiology , Osmotic Pressure , Animals , Models, Biological , Muscles/ultrastructureABSTRACT
A simple model is presented where, by an iterative procedure, the forces delivered by the power strokes are summed up to overcome the load. The system is moderated by the viscous hindrance. The model reproduces the features of muscle contraction as defined by the data of He et al. [1997. ATPase kinetics on activation of permeabilized isometric fibres from rabbit and frog muscle: a real time phosphate assay. J. Physiol. 501, 125-148] on rabbit psoas muscle fibres. According to the model power strokes are random. Energy summation take place if the subsequent power stroke occurs before the energy delivered by the previous power stroke is completely used. In order the sarcomere to be competent to contract initial driving force must reach a threshold whose value increases with the load. The step size of the power stroke decreases with the increase of the load. The viscous regime is simulated by the equation, where 1/k measures the viscous hindrance of the system. The relationship between water activity, viscosity and stiffness is discussed. It is concluded that the three parameters vary cyclically and that when water activity decreases (sarcomere shortening, cross-bridge attachment) viscosity and stiffness increase.
Subject(s)
Models, Biological , Muscle Contraction/physiology , Muscle, Skeletal/physiology , Viscosity , Animals , Osmotic Pressure , Sarcomeres/physiology , Stress, MechanicalABSTRACT
We present a model of muscle contraction based on purely physical grounds and modulated by a parameter, k, related to the visco-elastic hindrances of the contractile apparatus. The model predicts a strong cooperation among sarcomere units and proposes that viscous hindrance is a fundamental component of the economy of the contraction. The concept of cross-bridge step size is also discussed and it is concluded that the step size is of various and probably undeterminable length.
Subject(s)
Muscle Contraction/physiology , Sarcomeres/physiology , Adenosine Triphosphate/chemistry , Adenosine Triphosphate/physiology , Animals , Chemical Phenomena , Chemistry, Physical , Hydrolysis , Models, Theoretical , Rabbits , Sarcomeres/chemistryABSTRACT
We have found that polyacrylamide gels cross-linked with bisacrylamide induce a larger macromolecular osmotic pressure than the non cross-linked gels. This means also that in the cross-linked gels hydration water is held more tightly to the polymer, i.e., more work is needed to remove water, than in the non cross-linked gel. Since the chemical nature of the two gels is extremely similar, we propose that the formation of the network alters per se the water activity.
