肌肉收缩及自发振动的动力学理论

改变实验条件,肌纤维可发生从收缩到自发振动的相变。为了研究这一现象,引进了描述肌纤维内部弹性成分拉伸长度与张力关系的表达式,利用肌肉态方程并考虑肌纤维的特殊结构,给出了描述肌纤维收缩及自发振动的统一动力学方程。从动力学方程出发,肌纤维自发振动的发生条件得到了自然解释,所给出的振动周期和振动曲线同实验结果相符,并给出了一些新的理论结果。这一工作的意义在于,完成了从肌球蛋白单分子性质、肌纤维组织结构到肌纤维功能的信息整合。     

肌肉收缩的理论研究

基于肌球蛋白工作循环模型,从物理学的角度出发,利用化学动力学方法,给出肌动蛋白丝的动力学方程,讨论肌球蛋白的运力学行为,发现肌动蛋白运动呈锯齿状,并得到振动周期约为3.0s,与实验结果基本吻合。结论是宏观的肌肉运动是单分子运动的集体协同行为,为肌肉的运动训练和治疗提供理论参考。     

肌肉收缩Hill特性式的理论研究

从肌球蛋白工作循环的机械化学偶联模型出发,利用化学动力学方法和生物化学热力学原理,结合肌球蛋白单分子实验结果,从能量转化的观点给出了肌肉收缩的Hill特性式,加深了对Hill特性式及肌肉收缩过程中能量转化的理解,在整合肌球蛋白单分子性质与肌肉收缩宏观性质的信息方面做了尝试。     

肌肉收缩Hill特性式的理论研究

从肌球蛋白工作循环的机械化学偶联模型出发,利用化学动力学方法和生化热力学原理,结合肌球蛋白单分子实验结果,从能量转化的角度,研究了肌肉收缩过程中的力与速度关系,发现结果与Hill特性式基本一致。     

钾离子通道两态跳跃的通透机制

采用两态跳跃模型研究离子通道的通透机制,从两态动力学方程得到了平衡态下的能斯特方程、稳态条件下的米氏动力学关系。得出：若电压小于100mV,电导-电压关系是线性的;在电流-浓度关系中,电流具有饱和特性。这些与实验结果是一致的。此外,还讨论了钾离子通道到达稳态前的暂态过程,并用特征时间来描述这一过程。发现采用两态跳跃模型用较少的参数就可以说明离子通透的机制。     

肌球蛋白工作循环的机械化学偶联模型

目前在众多的分子马达中对骨骼肌肌球蛋白的研究较多,本文对肌球蛋白的结构、工作循环机制以及单分子动力学性质进行了探索。同时,对各种生化条件下肌纤维的收缩性质进行了测试。将Houdusse和Sweeney给出的机械化学偶联模型简化成一个新的四态模型,通过对定态时肌球蛋白态分布的研究,证明了简化模型的合理性。     

肌球蛋白动力冲程分布研究

通过建立肌球蛋白工作循环的四态模型,利用化学动力学方法,讨论了动力冲程过程的几率和无机磷酸盐的释放率是影响动力冲程分布的两个重要因素,得到动力冲程的大小近似呈均值为（8-10）nm的高斯分布。     

苏云金芽孢杆菌蛋白酶发酵动力学模型的构建

对苏云金芽孢杆菌FS140蛋白酶分枇发酵的代谢特性进行了研究.首先描述了FS140分枇发酵过程中细胞生长、产物积累、糖消耗的变化规律.基于Logistic方程和Luedeking-Piret方程,建立了苏云金芽孢杆菌蛋白酶发酵过程细胞生长、产物合成及基质消耗随时间变化的数学模型.动力学模型计算值结果与实验值拟合良好,较好反映了苏云金芽孢杆菌分批发酵过程的动力学特征.     

丝瓜肌球蛋白的电子显微学研究

从丝瓜(Luffa cylindrica (L.) Roem.)卷须中纯化得到分子量为174kD的肌球蛋白,并对其进行了酶学与电子显微学的研究.这种肌球蛋白具有肌动蛋白激活的MgATPase活性,能够被抗动物肌肉的肌球蛋白的单克隆抗体识别.电子显微学研究表明:它有两个头部(大小和形状与动物肌肉的肌球蛋白相似)和一条相对较短的尾部.还对丝瓜卷须的肌动蛋白进行了观测,偶尔发现一些尾部有球状结构的肌球蛋白.该肌球蛋白的免疫特性和超微结构证明了它由2条重链组成,并与传统的肌球蛋白相似.然而,这种174 kD的肌球蛋白是否参与了丝瓜的接触卷曲有待于进一步研究.     

种间竞争的一个新的数学模型—对经典的Lotka—Vol—terra竞争方程的扩充

本文根据营养动力学理论,建立了一类种间竞争的新的数学模型:它是单种群增长的Cui-Lawson模型,在种间竞争上的推广。新的种间竞争模型克服了经典的种间竞争的Lotka-Volteira方程的局限与不足,具有更广泛和复杂的行为,并在特殊条件下以Lotka-Volterra竞争方程为其特例。因此,新的种间竞争的数学模型是更一般的解释性模型,是对经典的Lotka-Voterra竞争方程的扩充。     

A model of muscle contraction based on the Langevin equation with actomyosin potentials

We propose a muscle contraction model that is essentially a model of the motion of myosin motors as described by a Langevin equation. This model involves one-dimensional numerical calculations wherein the total force is the sum of a viscous force proportional to the myosin head velocity, a white Gaussian noise produced by random forces and other potential forces originating from the actomyosin structure and intra-molecular charges. We calculate the velocity of a single myosin on an actin filament to be 4.9–49 μm/s, depending on the viscosity between the actomyosin molecules. A myosin filament with a hundred myosin heads is used to simulate the contractions of a half-sarcomere within the skeletal muscle. The force response due to a quick release in the isometric contraction is simulated using a process wherein crossbridges are changed forcibly from one state to another. In contrast, the force response to a quick stretch is simulated using purely mechanical characteristics. We simulate the force–velocity relation and energy efficiency in the isotonic contraction and adenosine triphosphate consumption. The simulation results are in good agreement with the experimental results. We show that the Langevin equation for the actomyosin potentials can be modified statistically to become an existing muscle model that uses Maxwell elements.     

Mechanochemical coupling in spin-labeled, active, isometric muscle

Observed effects of inorganic phosphate (P(i)) on active isometric muscle may provide the answer to one of the fundamental questions in muscle biophysics: how are the free energies of the chemical species in the myosin-catalyzed ATP hydrolysis (ATPase) reaction coupled to muscle force?. Pflugers Arch. 414:73-81) showed that active, isometric muscle force varies logarithmically with [P(i)]. Here, by simultaneously measuring electron paramagnetic resonance and the force of spin-labeled muscle fibers, we show that, in active, isometric muscle, the fraction of myosin heads in any given biochemical state is independent of both [P(i)] and force. These direct observations of mechanochemical coupling in muscle are immediately described by a muscle equation of state containing muscle force as a state variable. These results challenge the conventional assumption mechanochemical coupling is localized to individual myosin heads in muscle.     

Muscular contraction

A molecular theory of muscular contraction, based on the trigger action of the cross bridge between actin and myosin, is postulated. The formation of the cross bridge is followed by a transconformation in contractile protein producing work and liberating heat. The process possesses a mechanochemical character and utilizes the energy liberated by dephosphorylation of ATP. The equation of for tension dependence of muscle power is derived from the theory of reaction rates. The equation of is meaningful after elementary treatment; the physical meaning of the constants in these equations is explained. Quantitative analyses are corroborated by the experimental data.     

Kinetic model for isometric contraction in smooth muscle on the basis of myosin phosphorylation hypothesis.

A kinetic model was proposed to simulate an isometric contraction curve in smooth muscle on the basis of the myosin phosphorylation hypothesis. The Ca2+-calmodulin-dependent activation of myosin light-chain kinase and the phosphorylation-dephosphorylation reaction of myosin were mathematically treated. Solving the kinetic equations at a steady state, we could calculate the relationship between the Ca2+ concentration and the myosin phosphorylation. Assuming that two-head-phosphorylated myosin has an actin-activated Mg2+-ATPase activity and that this state corresponds to an active state, we computed the time courses of the myosin phosphorylation and the active state for various Ca2+ transients. The time course of the active state was converted into that of isometric tension by use of Sandow's model composed of a contractile element and a series elastic component. The model could simulate not only the isometric contraction curves for any given Ca2+ transient but also the following experimental results: the calmodulin-dependent shift of the Ca2+ sensitivity of isometric tension observed in skinned muscle fibers, the disagreement between the Ca2+ sensitivity of myosin phosphorylation and that of isometric tension at a steady state, and the disagreement between the time course of myosin phosphorylation and that of isometric tension development.     

Phosphorylation regulates the ADP-induced rotation of the light chain domain of smooth muscle myosin.

We have observed the effects of MgADP and thiophosphorylation on the conformational state of the light chain domain of myosin in skinned smooth muscle. Electron paramagnetic resonance (EPR) spectroscopy was used to monitor the orientation of spin probes attached to the myosin regulatory light chain (RLC). Two spectral states were seen, termed here "intermediate" and "final", that are distinguished by a approximately 24 degrees axial rotation of spin probes attached to the RLC. The two observed conformations are similar to those found previously for smooth muscle myosin S1; the final state corresponds to the major conformation of S1 in the absence of ADP, while the intermediate state corresponds to the conformation of S1 with ADP bound. Light chain domain orientation was observed as a function of the MgADP concentration and the extent of RLC thiophosphorylation. In rigor (no MgADP), LC domains were distributed equally between the intermediate state and the final state; upon addition of saturating (3.5 mM) MgADP, about one-third of the LC domains in the final state rotated approximately 20 degrees axially to the intermediate state. The progression of the change in populations was fit to a simple binding equation, yielding an apparent dissociation constant of approximately 110 microM for skinned smooth muscle fibers and approximately 730 microM for thiophosphorylated, skinned smooth muscle fibers. These observations suggest a model that explains the behavior of "latch bridges" in smooth muscle.     

Phosphatase inhibition with okadaic acid does not alter the relationship between force and myosin light chain phosphorylation in permeabilized smooth muscle

The phosphatase inhibitor, okadaic acid, has been used to test the hypothesis that myosin light chain phosphatase activity plays a central role in latchbridge formation in smooth muscle. In the permeabilized rabbit portal vein there is a non-linear relationship between myosin light chain phosphorylation and force production such that maximum force output occurs with about 50% phosphorylation. Treatment of the muscle with okadaic acid does not change this relationship even though there is a profound inhibition of phosphatase activity. The data suggest that dephosphorylation of the myosin light chain while the myosin is in the force producing state does not account for the high force output with low levels of light chain phosphorylation in smooth muscle.     

M-RIP targets myosin phosphatase to stress fibers to regulate myosin light chain phosphorylation in vascular smooth muscle cells

Vascular smooth muscle cell contraction and relaxation are directly related to the phosphorylation state of the regulatory myosin light chain. Myosin light chains are dephosphorylated by myosin phosphatase, leading to vascular smooth muscle relaxation. Myosin phosphatase is localized not only at actin-myosin stress fibers where it dephosphorylates myosin light chains, but also in the cytoplasm and at the cell membrane. The mechanisms by which myosin phosphatase is targeted to these loci are incompletely understood. We recently identified myosin phosphatase-Rho interacting protein as a member of the myosin phosphatase complex that directly binds both the myosin binding subunit of myosin phosphatase and RhoA and is localized to actin-myosin stress fibers. We hypothesized that myosin phosphatase-Rho interacting protein targets myosin phosphatase to the contractile apparatus to dephosphorylate myosin light chains. We used RNA interference to silence the expression of myosin phosphatase-Rho interacting protein in human vascular smooth muscle cells. Myosin phosphatase-Rho interacting protein silencing reduced the localization of the myosin binding subunit to stress fibers. This reduction in stress fiber myosin phosphatase-Rho interacting protein and myosin binding subunit increased basal and lysophosphatidic acid-stimulated myosin light chain phosphorylation. Neither cellular myosin phosphatase, myosin light chain kinase, nor RhoA activities were changed by myosin phosphatase-Rho interacting protein silencing. Furthermore, myosin phosphatase-Rho interacting protein silencing resulted in marked phenotypic changes in vascular smooth muscle cells, including increased numbers of stress fibers, increased cell area, and reduced stress fiber inhibition in response to a Rho-kinase inhibitor. These data support the importance of myosin phosphatase-Rho interacting protein-dependent targeting of myosin phosphatase to stress fibers for regulating myosin light chain phosphorylation state and morphology in human vascular smooth muscle cells.