Ion pores in biological membranes as self-organized bistable systems

Effects of mutual influence of photoinduced electron transitions and slow structural rearrangements in bacterial photosynthetic reaction centers

We describe the phenomenon of light-induced structural transformations in the reaction centers (RC) of photosynthetic bacteria which makes self-regulation of the RC charge separation efficiency possible. The nature of the effect is that the light-driven electron transfer (ET) between the RC redox-cofactors causes structural changes in the protein-cofactors system and this in turn affects the ET kinetics. If the electron-conformation interaction is strong enough, then such self-regulation gives birth to a new RC conformational state of enhanced charge separation efficiency. We show experimental results of stationary and kinetic absorbance change characteristics under different photoexcitation conditions, indicating structural rearrangements on a rather long (minutes) time scale, mainly within the secondary acceptor binding pocket. To simplify the description, in constructing a theory of structure-function reorganization in the RC we employ the adiabatic approach. Final expressions enable us to make qualitative comparison with experimentally observed kinetics of the fast and slow stages of 'free' and 'structurally controlled' electron relaxation, respectively.

Theory of single-file multiparticle diffusion in narrow pores

Single-file diffusion of multiple strongly interacting particles in a one-dimensional pore is described within a general analytical framework. The theory accounts for nonequilibrium conditions, explicit particle-particle interactions, external potential acting on the particles and the fluctuations of the number of particles due to their exchange with external equilibrium reservoirs. It is shown that the problem can be reduced to a closed hierarchical set of partial differential equations of increasing dimensionality, which can be solved numerically. Our framework allows computing any macroscopic characteristic of multiparticle diffusion in the pore. It is shown that the pore occupancy probabilities and the current are rational functions of external concentrations in the steady state. The theory is tested on a simplified model of the narrow rigid pore inspired by the selectivity filter of biological ion channel. Perspectives and limitations of the theory are discussed.

Weak extremely high frequency microwaves affect pollen-tube emergence and growth in kiwifruit: pollen grain irradiation and water-mediated effects

OBJECTIVE

This study was designed to evaluate the effects of weak-intensity extremely high frequency (EHF) microwaves in a model system-the plant organism pollen grain-lacking the placebo effect, available in large populations, to ensure accurate statistical analysis, and whose sensitivity is closely relevant to animal and human biology.

DESIGN

This study was blinded using an in vitro pollen germination technique. SUBJECTS AND STUDY INTERVENTIONS: Pollen of kiwifruit (Actinidia deliciosa) was either directly irradiated or grown in a medium prepared with irradiated water, using a CromoStim 2000, (PromoPharma, Republic of San Marino) designed for EHF microwave resonance therapy (MRT). It produces weak intensity EHF radiations (40-78 GHz), either continuous wave (cw) or modulated, at a 10 Hz-frequency, with infrared (IR) carried to 635-950 nm, and with an impedance (IPD) of 10(-21) W/Hz cm(2) and a power supply from 0 to 20 mW.

OUTCOME MEASUREMENTS

Pollen-tube emergence was expressed as a percent of grains producing a tube and tube elongation was measured at 4 hours of incubation by a turbidimetric assay (A(500)) of cultures, expressed as the net absorbance increase over time 0.

RESULTS

At days 2 and 4 during aging, both percent of germination and tube growth significantly and consistently improved over controls in kiwifruit pollen grains irradiated for 30 minutes at day 0 at 10 Hz frequency with the CromoStim 2000. Highly significant effects, either stimulant or inhibitory, were also observed on kiwifruit pollen (stressed or not) growing in a medium prepared with water previously irradiated either cw or modulated. Irradiated water affected pollen germination immediately and even after several days following EHF treatment.

CONCLUSIONS

Either direct or indirect EHF irradiation performed by the CromoStim 2000 is effective on pollen growth processes. In both cases, water seemed to play a primary role. According to the quantum electrodynamical coherence theory, our work could also have implications for homeopathy, suggesting a key to explain the efficacy of high dilutions and succussion procedures.

Self-regulation phenomena applied to bacterial reaction centers: 2. Nonequilibrium adiabatic potential: dark and light conformations revisited

Experimental and theoretical results in support of nonlinear dynamic behavior of photosynthetic reaction centers under light-activated conditions are presented. Different conditions of light adaptation allow for preparation of reaction centers in either of two different conformational states. These states were detected both by short actinic flashes and by the switching of the actinic illumination level between different stationary state values. In the second method, the equilibration kinetics of reaction centers isolated from Rhodobacter sphaeroides were shown to be inherently biphasic. The fast and slow equilibration kinetics are shown to correspond to electron transfer (charge separation) at a fixed structure and to combined electron-conformational transitions governed by the bounded diffusion along the potential surface, respectively. The primary donor recovery kinetics after an actinic flash revealed a pronounced dependence on the time interval (deltat) between cessation of a lengthy preillumination of a sample and the actinic flash. A pronounced slow relaxation component with a decay half time of more than 50 s was measured for deltat > 10 s. This component corresponds to charge recombination in reaction centers for which light-induced structural changes have not relaxed completely before the flash. The amplitude of this component depended on the conditions of the sample preparation, specifically on the type of detergent used in the preparation. The redox potential parameters as well as the structural diffusion constants were estimated for samples prepared in different ways.

Towards physical dynamic tolerance: an approach to resolve the conflict between free will and physical determinism

This paper attempts to resolve the conflict between free will and determinism. The problem is approached by demonstrating that: (a) some well-established experimental observations indicate that irreversibility persists at the molecular level, (b) microscopic reversibility is not fully compatible with macroscopic irreversibility, (c) an overall consistency can be maintained if microscopic reversibility is regarded only as an excellent approximation, whereas microscopic irreversibility together with chaos can account for macroscopic reversibility, and (d) endogenous noise serves a vital function of nerve excitation. Thus, the mean of position and momentum specified by a non-deterministic law of motion gives the law its superficially deterministic behavior and predictability, whereas its dispersion grants dynamic tolerance and irreversibility. Therefore, causality is preserved while a limited degree of freedom allows for the exercise of free will. However, it is argued that free will can never be proven or disproven by a conventional behavioral experiment.

A Stochastic Model of Conductance Transitions in Voltage-Gated IonChannels

We present a statistical physics model to describe the stochastic behaviorof ion transport and channel transitions under an applied membrane voltage.To get pertinent ideas we apply our general theoretical scheme to ananalytically tractable model of the channel with a deep binding site whichinteracts with the permeant ions electrostatically. It is found that theinteraction is modulated by the average ionic occupancy in the bindingsite, which is enhanced by the membrane voltage increases. Above acritical voltage, the interaction gives rise to a emergence of a newconducting state along with shift of S4 charge residues in the channel.This exploratory study calls for further investigations to correlate thecomplex transition behaviors with a variety of ion channels, withparameters in the model, potential energy parameters, voltage, and ionicconcentration.

Self-organized localization of macrostates by additive noise in a fast-slow dynamical system: effect of the slow nonreactive mode on the barrier crossing rate of the fast, bistable mode

We have studied the stochastic dynamics of a two-dimensional gradient system composed of a fast, bistable mode and a slow, monotonically decaying mode. The coupling is bidirectional and cooperative. Additive white noise acts on the fast mode only. We find that the noise intensity controls the location of macrostates (shape of the probability density function), the appearance of bimodality in the slow-mode probability distribution and, together with the coupling strength, the rate of fast-mode barrier crossing. These features arise from the interplay of noise, widely separated time scales, and bidirectional, excitatory coupling. They are believed to be generic.

Self-regulation phenomena in bacterial reaction centers. I. General theory

A model for light-induced charge separation in a donor-acceptor system of the reaction center of photosynthetic bacteria is described. This description is predicated on a self-regulation of the flow of photo-activated electrons due to self-consistent, slow structural rearrangements of the macromolecule. Effects of the interaction between the separated charges and the slow structural modes of the biomolecule may accumulate during multiple, sequential charge transfer events. This accumulation produces non-linear dynamic effects on system function, providing a regulation of the charge separation efficiency. For a biomolecule with a finite number of different charge-transfer states, the quasi-stationary populations of these states with a localized electron on different cofactors may deviate from a Lagmuir law dependence with actinic light intensity. Such deviations are predicted by the model to be due to light-induced structural changes. The theory of self-regulation developed here assumes that light-induced changes in the effective adiabatic potential occur along a slow structural coordinate. In this model, a "light-adapted" conformational state appears when bifurcation produces a new minimum in the adiabatic potential. In this state, the lifetime of the charge-separated state may be quite different from that of the "dark-adapted" conformation. The results predicted by this theory agree with previously obtained experimental results on photosynthetic reaction centers.

Computational dynamics of gradient bistable networks

We describe a neural-like, homogeneous network consisting of coupled bistable elements and we study its abilities of learning, pattern recognition and computation. The technique allows new possibilities of pattern recognition, including the memorization and perfect recall of several memory patterns, without interference from spurious states. When the coupling strength between elements exceeds a critical value, the network readily converges to a unique attractor. Below this critical value one could perfectly recall all memorized patterns.

Effects of nonequilibrium fluctuations on ionic transport through biomembranes

We investigate the effects of nonequilibrium fluctuations on ionic transport through ion channels in membranes using the concept of localized ratchet. Due to the localization, the ionic population in the binding site can be enhanced or suppressed depending upon ionic potential and its fluctuations, affecting the gating kinetics of the channel. The localized dichotomic fluctuations of ionic potential are shown to give rise to a current reversal differing from the results of periodic ratchets. It is also found that strong correlations between binding energy and membrane potential fluctuations induce resonancelike behaviors in ionic current as the fluctuating rate varies.

Ion regulation of the kinetics of potential-dependent potassium channels

We apply a theoretical approach developed earlier. The interaction ofions that permeate a channel with slowly relaxing charged channel-forminggroups (ion-conformational interaction - ICI) is addressed by thisapproach. One can describe the ion concentration influence (ion regulation)on channel functioning in this manner. A patch-clamp method in a'whole-cell' configuration is used to study the ICI. For this purpose theinfluence of an external concentration of potassium ions on thepotential-dependent potassium current (I(A)) in the externalmembrane of GH(3) cells was studied. The increase of[K(+) (out)] from 5 mM to 100 mM causes anon-monotonous shift of current-voltage dependencies. The dependence of bothan activation time constant tgr(n) and a steady-state activation(n(∞)) on [K(+)](out) have a minimum andmaximum respectively. The analysis of the results suggests that the observedeffects are caused by ICI. A physical model is developed to describe thedependence of the potassium channel kinetics on the external concentrationof the ions and the membrane potential. The 'deformation' of the closedstate of the gate and the corresponding energy shifts cause the observednon-monotonous dependencies due to ICI. Thus, the general theoreticalapproach has an experimental confirmation and is applied to concreteexamples. Formulas for concentrational dependencies of the channel kineticsare given for practical uses.

Dynamical self-organization in biomolecular systems of charge transport

Many non-linear and non-equilibrium aspects of the functioning of biomolecular objects indicate the effects of dynamical self-organization on the level of separate complexes or even individual macromolecules. Charge-conformational interactions provide a natural basis of molecular synergetic phenomena. Considering the charge transfer processes in ionic channels and photosynthetic reaction centres from this point of view, we exemplify recent theoretical and experimental results in its favour.