Two-time correlation functions and the Lee-Yang zeros for an interacting Bose gas.

Two-time correlation functions of a system of Bose particles are studied. We find a relation of zeros of the correlation functions with the Lee-Yang zeros of the partition function of the system. The obtained relation gives the possibility to observe the Lee-Yang zeros experimentally. A particular case of Bose particles on two levels is examined, and zeros of two-time correlation functions and Lee-Yang zeros of the partition function of the system are analyzed.

Focusing in multiwell potentials: applications to ion channels.

We investigate nonequilibrium stationary distributions induced by stochastic dichotomous noise in double-well and multiwell models of ion channel gating kinetics. The channel kinetics is analyzed using both overdamped Langevin equations and master equations. With the Langevin equation approach we show a nontrivial focusing effect due to the external stochastic noise, namely, the concentration of the probability distribution in one of the two wells of a double-well system or in one or more of the wells of the multiwell model. In the multiwell system, focusing in the outer wells is shown to be achievable under physiological conditions, while focusing in the central wells has proved possible so far only at very low temperatures. We also discuss the strength of the focusing effect and obtain the conditions necessary for maximal focusing to appear. These conditions cannot be predicted by a simple master equation approach.

Human red blood cells' physiological water exchange with the plasma.

In the present paper, fundamental issues related to the mechanisms of human red blood cells' physiological water exchange with the plasma (for the stationary conditions) have been discussed. It has been demonstrated, on the basis of mechanistic transport equations for membrane transport that red blood cells are capable of exchanging considerable amounts of water with the plasma. Water absorption is osmosis-driven, and its removal occurs according to the hydromechanics principle, i.e. is driven by the turgor pressure of red blood cells. This newly-acquired knowledge of these issues may appear highly useful for clinical diagnosis of blood diseases and blood circulation failures.

Optimal-sensitivity analysis of ion channel gating kinetics.

We propose a new approach to analysis of kinetic models for ion channel gating, based on application of fluctuating voltages through a voltage clamp, in addition to conventional techniques. We show that the channel kinetics can be probed in a much more sensitive way, leading to more efficient model selection and more reliable estimates of model parameters. We use wavelet transform as an analytic tool for fluctuating currents and parametric dispersion plots as a measure of model compatibility with experimental data.

Application of oscillating potentials to the Shaker potassium channel.

Nonequilibrium response spectroscopy (NRS) has been proposed recently to complement standard electrophysiological techniques used to investigate ion channels. It involves application of rapidly oscillating potentials that drive the ion channel ensemble far from equilibrium. It is argued that new, so far undiscovered features of ion channel gating kinetics may become apparent under such nonequilibrium conditions. In this paper we explore the possibility of using regular, sinusoidal voltages with the NRS protocols to facilitate Markov model selection for ion channels. As a test case we consider the Shaker potassium channel for which various Markov models have been proposed recently. We concentrate on certain classes of such models and show that while some models might be virtually indistinguishable using standard methods, they show marked differences when driven with an oscillating voltage. Model currents are compared to experimental data obtained for the Shaker K+ channel expressed in mammalian cells (tsA 201).

Mechanistic formalism for membrane transport generated by osmotic and mechanical pressure.

Since the physical interpretation of practical Kedem-Katchalsky (KK) equations is not clear, we consider an alternative, mechanistic approach to membrane transport generated by osmotic and hydraulic pressure. We study a porous membrane with randomly distributed pore sizes (radii). We postulate that reflection coefficient (sigma p) of a single pore may equal 1 or 0. From this postulate we derive new (mechanistic) transport equations. Their advantage is in clear physical interpretation and since we show they are equivalent to the KK equations, the interpretation of the latter became clearer as well. Henceforth the equations allow clearer and more detailed interpretation of results concerning membrane mass transport. This is especially important from the point of view of biophysical studies on permeation processes across biological membranes, cell membranes including.

Mechanistic equations for membrane substance transport and their identity with Kedem-Katchalsky equations.

Since the physical interpretation of practical Kedem-Katchalsky (KK) equations is not clear, we consider an alternative, mechanistic approach to membrane transport generated by osmotic and hydraulic pressure. We study a porous membrane with randomly distributed pore sizes (radii). We postulate that reflection coefficient (sigma(p)) of a single pore may equal 1 or 0. From this postulate we derive new (mechanistic) transport equations. Their advantage is in clear physical interpretation and since we show they are equivalent to the KK equations, the interpretation of the latter became clearer as well. Hence the equations allow clearer and more detailed interpretation of results concerning membrane substances transport.

Wavelet analysis of nonequilibrium ionic currents in human heart sodium channel (hH1a).

Nonequilibrium response spectroscopy (NRS), the technique of using rapidly fluctuating voltage pulses in the study of ion channels, is applied here. NRS is known to drive an ensemble of ion channels far from equilibrium where, it has been argued, new details of ion channel kinetics can be studied under nonequilibrium conditions. In this paper, a single-pulse NRS technique with custom-designed waveforms built from wavelets is used. The pulses are designed to produce different responses from two competing models of a human heart isoform of the sodium channel (hH1a). Experimental data using this new type of pulses are obtained through whole-cell recordings from mammalian cells (HEK 293). Wavelet analysis of the model response and the experimental data is introduced to show how these NRS pulses can aid in distinguishing the better of the two models and thus introduces another important application of this new technique.

Studies on the structural properties of porous membranes: measurement of linear dimensions of solutes.

This work is concerned with a novel way of studying the basic structural and transport properties of porous membranes. Formulae have been derived for: the total number (N) of pores in the membrane; and mean square radius (r(k)) of pores and for selective membranes: the mean square radius (r(ka)) of pores impermeable to solutes and mean square radius (r(kb)) of permeable pores. The result of the investigation is the proposal of a new research procedure (osmotic) for the determination of the linear dimensions of solutes.

Modification and quantitative analysis of the Münch model in the integrated system of water translocation in plants.

Aiming at making the Münch model more adequate to the biological reality we introduce certain modifications and complements. Considering the model within the framework of so-called integrated system of long-distance water transport in plants we present a quantitative analysis based on the Kedem-Katchalsky formalism. A new mathematical description of the reverse osmosis is also utilized. The work is a starting point for further quantitative studies and simulations of the phloem transport of water and assimilates in plants.

Membrane Transport Generated by the Osmotic and Hydrostatic Pressure. Correlation Relation for Parameters L(p), σ, and ω.

Standard approach to membrane transport generated by osmotic andhydrostatic pressures, developed by Kedem and Katchalsky, is based onprinciples of thermodynamics of irreversible processes. In this paper wepropose an alternative technique. We derive transport equations from fewfairly natural assumptions and a mechanistic interpretation of the flows.In particular we postulate that a sieve-type membrane permeability isdetermined by the pore sizes and these are random within certain range.Assuming that an individual pore is either permeable or impermeable tosolute molecules, the membrane reflection coefficient depends on the ratioof permeable and impermeable pores. Considering flows through permeableand impermeable pores separately, we derive equations for the total volumeflux, solute flux and the solvent flux across the membrane. Comparing themechanistic equations to the Kedem-Katchalsky equations we find the formereasier to interpret physically. Based on the mechanistic equations we alsoderive a correlation relation for the membrane transport parameters L(p),σ, and ω. This relation eliminates the need for experimentaldetermination of all three phenomenological parameters, which in somecases met with considerable difficulties.

A Description of Reverse Osmosis using Practical Kedem-Katchalsky Equations.

The work is concerned with an analytical description of reverseosmosis using the Kedem-Katchalsky equations.The process has been considered for well-mixed solutions.We have obtained formulas describing the concentration of a solution(purified by reverse osmosis) as a function of the transportparameters of a membrane, concentration of the initial solution, andthe mechanical pressures on the membrane.The formulae are illustrated by numerical computations.Our results may be applicable to biophysical studies concerningreverse osmosis in biological membrane systems.

Correlation Relation for the Membrane Transport ParametersL(p), σ, and ω.

We derive a formula for the correlation of the three practical transportparameters L(p), σ, and ω appearing in Kedem-Katchalskyequations. It has a form ω = KL(p)/v(s)(1-σ), where K = 0.0306 is a universal constant independent ofthe choice of a membrane and a solute. It can be used to calculate the valueof any of these parameters, provided the other two and the molar volume[Formula: see text] of the solute are known. The formula couldbe very useful, in particular when measurements of the parameters aredifficult or even impossible.

The plant root as an osmo-diffusive converter of free energy.

This work focuses on the maize root as a one-membrane osmo-diffusive converter of free energy. Energy expenditures of the root on water transport by radial route as well as on xylem water uptake, occurring according to the principle of osmotic root pressure, are analyzed. The so-called practical method of osmo-diffusive energy conversion (Kargol 1990, 1993) and experimental data taken from the work by Steudle et al. (1987) were employed, including coefficients of filtration (Lpr), reflection (sigma) and permeation (omega) of the maize root treated as a one-membrane model system. It is shown a.o. that the energy efficiency of the root does not depend (within a certain concentration interval) on the concentration of a given solute in solution into which the root is placed. This suggests a certain independence of environmental conditions. The efficiency is different for different dissolved substances contained in the solution.