Shot noise in ion channels.

A theoretical treatment of electrical noise originating from the discontinuous movement of ions through pore-like channels in a membrane is given. Two simple models are considered, a port with a single energy barrier and a pore with a single binding site separated from the aqueous solutions by energy barriers on either side. The single-barrier pore acts as a white-noise source with a spectral density SJ of the current that is proportional to the total rate of jumps over the barrier. At voltages near the equilibrium potential of the permeable ion, SJ becomes equal to the spectral density of thermal (or Johnson) noise. On the other hand, in the limit of high voltages, SJ approaches the spectral density of a Schottky noise source. A similar behaviour is found for channels with a double barrier in the limit of low frequencies omega. At higher frequencies a dispersion of the spectral density near omega = 1/tau1 occurs, where tau1 is the average lifetime of the occupied state of the channel.