ABSTRACT
A set of five differential equations has been found which gives a satisfactory account of the isotonic and isometric properties of striated muscle. Four of these differential equations give an equally satisfactory account of the results of length-drive experiments with sinusoidal variation of length. In this case, the fifth equation (of motion) is redundant. These sets of equations predict a number of results not yet measured relating to the superposition of oscillatory length changes on isotonic contraction. The equations predict correctly the variation of tension with time when the amplitude of the driven oscillation increases beyond the region where it can be treated as a perturbation, and the deviation of the mean tension per cycle from the steady-state tension for isotonic contraction with superimposed oscillations in length or velocity. The equations can be derived rigorously from a more complex set of eight equations which themselves are formulated from the basic principles of chemical physics, the theory of molecular force fields and radiationless transitions. The reduced model may be consistent with many other molecular theories and its predictive success does not prove the correctness or otherwise of the level 1 assumptions of the seven-state theory. By the same token, macroscopic mechanical experiments of the type presently carried out cannot give information on level 1 questions such as the existence or otherwise of 'binding' of crossbridges to the thin filament. The experimental kinetic results can be described with or without this assumption. The theory needs considerable development in so far as it does not consider elastic elements at all at present, nor have detailed conclusions yet been extracted from the equations for the case of stretching, except for isotonic steady states where agreement is encouraging.
Subject(s)
Models, Biological , Muscle Contraction , Muscles/physiology , Adenosine Triphosphate/metabolism , Animals , Biomechanical Phenomena , Energy Metabolism , Humans , Insecta/physiology , Kinetics , RabbitsABSTRACT
The set of kinetic equations that defines a deterministic model of muscle contraction, based on the sliding filament hypothesis in which the relative sliding velocity is an independent variable, is numerically integrated under the simulated conditions of sinusoidal length perturbation. The frequency response curve of phase angle and dynamic stiffness are in agreement with experimental curves. The resultant mean tension per cycle is lower than the unperturbed steady-state tension. The magnitude of the negative tension deviation is greater when either the amplitude or the frequency of the oscillation is increased. The tension-time curve differs from a simple sine when the perturbing frequency is in the vicinity of the stiffness minimum. These consequences are in agreement with the few experimental results that are available.
Subject(s)
Models, Biological , Muscle Contraction , Animals , Biomechanical Phenomena , Sarcomeres/physiologySubject(s)
Basal Metabolism , Models, Biological , Body Temperature Regulation , Humans , TemperatureABSTRACT
The production of chemo-mechanical effects in a reconstituted system of purified muscle proteins had been studied. It was found that the "streaming" effects observed (by previous workers) in the circular slit of a stream cell were observed under conditions where the absence of artefacts could not be guaranteed. In particular, convective motion motion, due to small temperature gradients is shown to be present, resulting in streaming even in the absence of essential components of the system such as ATP. Temperature inhomogeneities of the order of only 0.1 K . mm-1 are sufficient to cause motion, and any future experiments on streaming must be thermally homogeneous to a greater accuracy than this if valid conclusions are to be drawn.
Subject(s)
Actins , Adenosine Triphosphatases/metabolism , Myosin Subfragments , Animals , Chemical Phenomena , Chemistry, Physical , Muscle Contraction , Rabbits , TemperatureSubject(s)
Adenosine Triphosphate/physiology , Models, Biological , Muscle Contraction , Animals , Kinetics , Muscles/physiologySubject(s)
Body Temperature Regulation , Head , Models, Biological , Cold Temperature , Environment , HumansABSTRACT
An apparatus designed to study the growth rates of surface colonies in constant conditions, i.e. not affected by nutrient diffusion as in a closed Petri dish, is described. In contrast to classical experiments in closed systems, an exponential growth of colony radius is obtained for a period of more than 72 h. Nutrient concentration gradients are shown to be eliminated by analytical techniques.
Subject(s)
Saccharomyces cerevisiae/growth & development , Cell Division , Culture Media , Diffusion , EnvironmentABSTRACT
The effect of feed alcohol in an apparatus designed to study growth rates of surface colonies in constant nutrient conditions was studied. The results obtained indicate that departure from exponential growth in normal conditions is due to accumulation of alcohol in the system.
Subject(s)
Ethanol/pharmacology , Saccharomyces cerevisiae/growth & development , Cell Division , Culture Media , Environment , Saccharomyces cerevisiae/drug effectsABSTRACT
The growth rates of yeast surface colonies under constant nutrient conditions were studied as a function of nutrient concentration. This was complementary to the initial experiment to measure the rates under such conditions, and to the investigation of the effects of alcohol. The possibility of fitting an equation of the Michaelis-Menten type to the variation of growth rate with carbon source concentration is considered.
