Activation kinetics of T-type calcium channel by a path probability approximation

Özer, Mahmut

Article | 2004 | NeuroReport15 ( 9 ) , pp.1451 - 1455

We previously formulated dynamics of ion channel gates by the path probability method. In this study, we apply that theoretical approach to derive the activation rate kinetics of T-type calcium channel in thalamic relay neurons. We derive explicit expressions of the forward and backward rate constants and show that the proposed rate constants accurately capture form of the empirical time constant, and that they also provide its saturation to a constant value at depolarized membrane potentials. We also compare our derivations with linear and nonlinear thermodynamic models of rate kinetics obtained from the same calcium channel, and s . . .how that it is possible to capture saturation of the time constant for the depolarized membrane potentials by the only proposed rate constants. © 2004 Lippincott Williams & Wilkins Daha fazlası Daha az

Impact of synaptic noise and conductance state on spontaneous cortical firing

Özer, Mahmut | Graham, Lyle J. | Erkaymaz, Okan | Uzuntarla, Muhammet

Article | 2007 | NeuroReport18 ( 13 ) , pp.1371 - 1374

Cortical neurons in-vivo operate in a continuum of overall conductance states, depending on the average level of background synaptic input throughout the dendritic tree. We compare how variability, or fluctuations, in this input affects the statistics of the resulting 'spontaneous' or 'background' firing activity, between two extremes of the mean input corresponding to a low-conductance (LC) and a high-conductance (HC) state. In the HC state, we show that both firing rate and regularity increase with increasing variability. In the LC state, firing rate also increases with input variability, but in contrast to the HC state, firing re . . .gularity first decreases and then increases with an increase in the variability. At high levels of input variability, firing regularity in both states converge to similar values. © 2007 Lippincott Williams & Wilkins, Inc Daha fazlası Daha az

Weak signal propagation through noisy feedforward neuronal networks

Özer, Mahmut | Perc, Matjaž | Uzuntarla, Muhammet | Koklukaya, Etem

Article | 2010 | NeuroReport21 ( 5 ) , pp.338 - 343

We determine under which conditions the propagation of weak periodic signals through a feedforward Hodgkin-Huxley neuronal network is optimal. We find that successive neuronal layers are able to amplify weak signals introduced to the neurons forming the first layer only above a certain intensity of intrinsic noise. Furthermore, we show that as low as 4% of all possible interlayer links are sufficient for an optimal propagation of weak signals to great depths of the feedforward neuronal network, provided the signal frequency and the intensity of intrinsic noise are appropriately adjusted. © 2010 Wolters Kluwer Health | Lippincott Wil . . .liams & Wilkins Daha fazlası Daha az

A new methodology to define the equilibrium value function in the kinetics of (in)activation gates

Özer, Mahmut | Erdem, Rıza

Article | 2003 | NeuroReport14 ( 7 ) , pp.1071 - 1073

A voltage-gated ion channel is fundamental in generation and propagation of electrical signals in the excitable membranes. Dynamics of (in)activation gates of the ion channel is modeled by first-order kinetics. The equilibrium value function is crucial in the kinetics of the (in)activation gates for fitting experimental data. We present a new methodology to define the equilibrium value function based on the lowest approximation of the cluster variation method and the static properties in the molecular field approximation. The methodology allows for exploration of the gating dynamics. © 2003 Lippincott Williams & Wilkins.

An improved non-linear thermodynamic model of voltage-dependent ionic currents

Özer, Mahmut

Article | 2004 | NeuroReport15 ( 12 ) , pp.1953 - 1957

Thermodynamic models of ionic currents are used to deduce exact functional form of rate constant. It is first assumed that free energy depends linearly on voltage. A major criticism of this approach is that time constant can reach arbitrarily small values resulting in an aberrant behavior. Recently, non-linear effects of electric field on the free energy were considered to solve this problem based on T-type calcium channel. In this study, we show that the current model approximately captures the voltage-dependence of the time constant only in a specific range of voltage and does not provide saturation of the time constant outside th . . .is range. Then, we propose an improved non-linear thermodynamic model and illustrate its applicability based on T-type calcium channel. © 2004 Lippincott Williams & Wilkins Daha fazlası Daha az

A new approach to define dynamics of the ion channel gates

Özer, Mahmut | Erdem, Rıza | Provaznik, Ivo

Article | 2004 | NeuroReport15 ( 2 ) , pp.335 - 338

Voltage-gated ion channels are of great importance in the generation and propagation of electrical signals in the excitable cell membranes. How these channels respond to changes in the potential across the membrane has been a challenging problem, and different approaches have been proposed to address the mechanism of voltage sensing and gating in these channels. In this study, we attempt a new approach by considering a simple two-state gate system and applying the path probability method to construct a nonequilibrium statistical mechanical model of the system. The model which is based on the principles of statistical physics provide . . .s a firm physical basis for ion channel gating. © 2004 Lippincott Williams & Wilkins Daha fazlası Daha az

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