Dielectric noise in membranes.

Most theoretical and experimental studies of electrical fluctuations in membranes so far have been devoted to noise associated with conduction processes. In this paper a different type of noise is described which results from dipolar transitions in the membrane. Two mechanisms for the generation of such dielectric noise are analyzed: (a) conformational transitions of membrane proteins involving changes in dipolar moment and/or polarizibility, and (b) rotation of dipolar molecules dissolved in the lipid. The spectral intensity of current noise calculated for the two models exhibits a characteristic dependence on frequency omega with a decrease proportional to omega 2 towards low frequencies and an approach to a frequency-independent (white noise) limit at high frequencies. For a given number of dipolar molecules in the membrane, the spectral intensity is inversely proportional to the square of the membrane thickness.