l/f noise in black lipid membranes induced by ionic channels formed by chemically dimerized gramicidin A.

The noise behavior of lipid bilayer membranes, doped with a chemically dimerized gramicidin A, was investigated. In contrast to normal gramicidin A, which generates a Lorentzian type power spectrum due to the formation and disappearance of conducting dimers, the current power spectrum density Sm(f) obtained with this gramicidin A derivative showed over several orders of magnitude a clear l/f behavior. The intensity of this l/f component was analyzed as a function of the membrane-applied voltage, membrane resistance, electrolyte concentration, and composition. The relationship between the mean-square fluctuation in current and the membrane current mean value was found to follow Hooge's equation, i.e., deltaI2 = alphaI2m/Nf where N is the number of channels and alpha is a constant equal to 1.0 X 10(-2). It is suggested that a l/f type noise was observed because the chemically dimerized form of gramicidin A produces long lasting cation selective channels.