STOCHASTIC RESONANCES IN ACTIVE-TRANSPORT IN BIOLOGICAL-MEMBRANES

It is shown that experimental data (D.-S. Liu, R.D. Astumian, T.Y. Tso ng, J. Biol. Chem. 265, 7260 (1990)) on active transport of Na+ in hum an erythrocytes (catalyzed by Na+-K+-ATPase) under the influence of ex ternal ac electric fields can be interpreted as the evidence of stocha stic resonance between the external ac field and the fluctuations of t he membrane potential (energy barrier of the process): the signal-to-n oise ratio J/gamma(i), where J is the ionic current (signal), gamma(i) - the intensity of intrinsic fluctuations (noise), exhibits strong ma ximum as the function of gamma(i). The model calculations show that in the considered system one can expect the appearance of (i) inverse st ochastic resonance, and of (ii) aperiodic stochastic resonance: (i) th e ratio J/psi(a) vs intensity of external ac field psi(a), exhibits ma ximum in the presence of barrier fluctuations; (ii) the exterIlal peri odic ac field can be replaced by the external random ac field (dichoto mous Markovian noise in our calculations) of strength gamma(e) and inv erse correlation time Lambda(e), and the ratio J/gamma(e), vs. gamma(e ) also exhibits a distinct maximum in the presence of internal fluctua tions of the membrane potential. Note that the superposition of two Ma rkovian dichotomous noises (internal fluctuations and external ac fiel d) is equivalent to non-Markovian barrier fluctuations.