Publications

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 ionic concentration.

An ion channel is a macromolecular machinery (NANOMACHINE) which regulates the ionic conduction through biomembranes. The ion channels are fundamental in every thought, every perception, every movement, and every heartbeat. The relevant biological dynamics in mesoscopic level is the overdamped slow dynamics. We present a stochastic model to describe the coupled behaviors of ion transport and channel conformation under an applied (trans)membrane potential. We apply our general theoretical formulae to an analytically tractable model of channel with a deep binding site which interacts with the permeant ions electrostatically or entropically. The interaction is found to be modulated by the ionic occupancy which is enhanced by the membrane potential. Above a critical interaction strength or a membrane potential, the interaction gives rise to an emergence of a new conductance state, via a channel conformational transition. This is the self-organization generic to strongly coupled stochastic processes.

We propose a short-period dispersion-managed fiber that consisted of conventional single-mode fiber (17 ps/km/nm) and negative dispersion fiber (-15 ps/km/nm). Thus, the average dispersion of the proposed fiber was only 1 ps/km/nm. The lengths of the positive and negative fiber sections were only 4.5 km so that they can be accommodated within a single 9-km-long cable. We evaluated the performance of this fiber using a 320-Gb/s (32/spl times/10 Gb/s) WDM system with 50-GHz channel spacing. After 563-km transmission, the average Q-factor was measured to be better than 18 dB without any dispersion compensation.

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.