STOCHASTIC RESONANCE IN THERMALLY ACTIVATED REACTIONS - APPLICATION TO BIOLOGICAL ION CHANNELS

At the molecular level many thermally activated reactions can be viewe d as Poisson trains of events whose instantaneous rates are defined by the reaction activation barrier height and an effective collision fre quency. When the barrier height depends on an external parameter, vari ation in this parameter induces variation in the event rate.:Extending our previous work, we offer a detailed theoretical analysis of signal transduction properties of these reactions considering the external p arameter as an input signal and the train of resulting events as an ou tput signal. The addition of noise to the system input facilitates sig nal transduction in two ways. First; for a linear relationship between the barrier height and the external parameter the output signal power grows exponentially with the mean square fluctuation of the noise. Se cond, for noise of a sufficiently high bandwidth, its addition increas es output signal quality measured as the signal-to-noise ratio (SNR). The output SNR reaches a maximum at optimal noise intensity defined by the reaction sensitivity to the external parameter, reaction initial rate, and the noise bandwidth. We apply this theory to ion channels of excitable biological membranes. Based on classical results of Hodgkin and Huxley we show that open/closed transitions of voltage-gated ion channels can be treated as thermally activated reactions whose activat ion barriers change linearly with applied transmembrane voltage. As an experimental example we discuss our recent results obtained with poly peptide alamethicin incorporated into planar lipid bilayers. (C) 1998 American Institute of Physics.