Membrane shot-noise in electrically depolarized nodes of Ranvier.

Abstract

The power spectra of the spontaneous voltage fluctuations (membrane noise) of the node of Ranvier were measured in the frequency range from 0.3 to 1500 cycles per second at different levels of the membrane potential (−90 to +30 mV, inside negative). Up from about −30 mV the power spectrum shows a\(\frac{1}{{1 + \left( {2\pi f\tau } \right)^2 }}\) component, which increases with depolarization. This shot like noise component is independent of and occurs in addition to the 1/f component. The source of this shot like noise component is probably given by fluctuations in the conductance for potassium ions. With the use of a minimum parameter model which consists of channels that switch randomly in time from the closed to the open state and vice versa, independent of each other, the number of active channels per μm2 appears to be of the order of 1000. The elementary unit of the potassium system conductance is then of the order of 10−11S per channel1 and the mean frequency of switches per second per channels is about 160.