Current noise generated by electrogenic ion pumps

Active ion transport by ATP- or light-driven pumps involves a sequence of elementary steps such as binding and release of ions, as well as conformational transitions of the pump protein. At the microscopic level the individual reaction steps occur at random intervals, and therefore the current generated by electrogenic pumps fluctuates around a mean value. In this paper, a theoretical treatment of the electrical noise associated with active ion transport is given. The analysis, which is based on the calculation of the correlation function, yields the spectral intensity S1 of current noise as a function of frequency, f. The shape of S1(f) contains information on the rate constants as well as on the magnitude of the charge displacements occurring during single reaction steps. The contribution of electrogenic pumps to the total voltage noise of the cell may be estimated from S1(f) and from the frequency-dependent impedance of the cell membrane.