Zhao Tong-Jun

The synchronization of FitzHugh-Nagumo neuron network coupled by gap junction ∗

It is well known that the strong coupling can synchronize a network of nonlinear oscillators. Synchronization provides the basis of the remarkable computational performance of the brain. In this paper the FitzHugh–Nagumo neuron network is constructed. The dependence of the synchronization on the coupling strength, the noise intensity and the size of the neuron network has been discussed. The results indicate that the coupling among neurons works to improve the synchronization, and noise increases the neuron random dynamics and the local fluctuations; the larger the size of network, the worse the synchronization. The dependence of the synchronization on the strength of the electric synapse coupling and chemical synapse coupling has also been discussed, which proves that electric synapse coupling can enhance the synchronization of the neuron network largely.

Model for Influences of Magnetic Fields on Intracellular Calcium Oscillations

Based on the model of the two calcium stores developed by Goldbeter, the influence of external magnetic field on the calcium concentration has been discussed. We believe that the cell membrane is a major site of interaction for extremely-low-frequency (ELF) electromagnetic fields, and the permeability of ions can be changed with the changing electromagnetic fields. It is shown that magnetic field initiates intracellular calcium oscillation with a threshold in flux density, and that the calcium oscillations do not occur if the density of magnetic field is below the threshold. The results of theoretical calculation are consistent with that of the experiment. The intracellular free calcium concentrations of different cells exposed to the same magnetic fields are different from each other. It is indicated that the different behaviors such as oscillation, rise and invariability of calcium concentration are associated with the sort of cells.

Mechanism of Permeation in Calcium Channels Activation by Applied Magnetic Fields

In this paper, a Brownian dynamics model of cell membrane calcium ion channels exposure to ELF magnetic fields has been proposed for the first time. Based on the model, the permeation of calcium channels activation by applied magnetic fields is given here. The number of opened calcium channel is increase with magnetic fields. The currents of calcium ions in the channel in controls and exposure to ELF magnetic fields are almost the same. These results are consistent with experiments. Thus it can be seen that the current of single calcium channel was nearly unaffected by applied magnetic fields, the increased number of opened calcium channel may be the reason of increased intracellular calcium concentration.

Environmental Impacts on Spiking Properties in Hodgkin–Huxley Neuron with Direct Current Stimulus

Based on the well accepted Hodgkin–Huxley neuron model, the neuronal intrinsic excitability is studied when the neuron is subject to varying environmental temperatures, the typical impact for its regulating ways. With computer simulation, it is found that altering environmental temperature can improve or inhibit the neuronal intrinsic excitability so as to influence the neuronal spiking properties. The impacts from environmental factors can be understood that the neuronal spiking threshold is essentially influenced by the fluctuations in the environment. With the environmental temperature varying, burst spiking is realized for the neuronal membrane voltage because of the environment-dependent spiking threshold. This burst induced by changes in spiking threshold is different from that excited by input currents or other stimulus.

Stochastic Four-State Mechanochemical Model of F1-ATPase

F1-ATPase, a part of ATP synthase, can synthesize and hydrolyze ATP moleculars in which the central γ-subunit rotates inside the α3 β3cylinder. A stochastic four-state mechanochemical coupling model of F1-ATPase is studied with the aid of the master equation. In this model, the ATP hydrolysis and synthesis are dependent on ATP, ADP, and Pi concentrations. The effects of ATP concentration, ADP concentration, and the external torque on the occupation probability of binding-state, the rotation rate and the diffusion coefficient of F1-ATPase are investigated. Moreover, the results from this model are compared with experiments. The mechanochemical mechanism F1-ATPase is qualitatively explained by the model.

Monte Carlo Simulation of the Permeability of Calcium Channels Exposure to Electromagnetic Fields

In this paper, a new approach is proposed to model permeation of calcium channels activation by applied magnetic fields. The curves of average velocity and displacement of calcium ions in the channels exposed to ELF magnetic fields are obtained, and they are higher than the controls. The relative numbers of calcium ions in ELF magnetic field stimulated channels is no different from that of controls. The increased number of opened calcium channel may be the reason of increased intracellular calcium concentration.

The spike timing precision of FitzHugh-Nagumo neuron network coupled by gap junctions

It has been proved recently that the spike timing can play an important role in information transmission, so in this paper we develop a network with N-unit FitzHugh–Nagumo neurons coupled by gap junctions and discuss the dependence of the spike timing precision on synaptic coupling strength, the noise intensity and the size of the neuron ensemble. The calculated results show that the spike timing precision decreases as the noise intensity increases; and the ensemble spike timing precision increases with coupling strength increasing. The electric synapse coupling has a more important effect on the spike timing precision than the chemical synapse coupling.

Motion and Efficiency of a Two-State Model for a Single Molecular Motor*

We discussed the directed motion and the energy conversion efficiency of a particle in two-state ratchet potentials with white noise. We studied the effective potential of multi-state. The two-state potential is equivalent to an effective potential that has a nonzero average slope on a large scale in general. The incline of the effective potential is crucial to the directed motion and the efficiency. We also discussed the relationship between the efficiency and the kinetic parameters such as the strength of the noise and the transition rates between the two states. We notice that there exists a maximal efficiency when the noise strength and the fluctuating rates take appropriate values.

Directed Motion of a Molecular Motor Based on the Four-State Model with Unequal Substeps

A periodic one-dimensional four-state hopping model is proposed. In the model, the substeps between arbitrary adjacent states are unequal, and an explicit solution of the master equation is first obtained for the probability distribution as a function of the time and position for any initial distribution with all the transients included. Next, the transient behaviors in the initial period of time and the characteristic time to reach the steady state for the molecular motor are discussed. Finally, we compare the steady state results to experiments and illustrate qualitatively the kinetic behaviors of a molecular motor under external load F.

A Flashing Model for Transport of Brownian Motors

A flashing coloured noise model is proposed to describe the motion of a molecular motor. In this model, the overdamped Brownian particle moves in an asymmetric periodic potential with a flashing Ornstein-Ulenbeck coloured noise. The relationship between the current and the parameters - such as the intensity, the correlation time of coloured noise and the flip rate of the noise - is discussed using the Monte Carlo simulation method. Current reversal occurs with the change of the correlation time and the flip rate of coloured noise, which may be related to the directed motion and the current reversal of molecular motors.