Monte-Carlo-simulations of voltage fluctuations in biological membranes in the case of small numbers of transport units.

Some years ago a theory of non-equilibrium voltage fluctuations in biological membranes was developed (Frehland and Solleder 1985, 1986) under a linearisation condition which is valid for a great number of transport units. In order to get an insight into the stochastic behaviour of such systems, consisting of small numbers of transport units, we carried out Monte-Carlo-simulations and compared the mean voltage course and the spectral density with the results of the previous theory. Under parameter conditions of biological relevance no significant differences from the behaviour of systems with large numbers, as predicted from the earlier theory, could be found in the case of rigid pores and ion carriers. However, in the case of small numbers, channels with open-closed-kinetics showed great deviation. With increasing number of transport units agreement with the previous theory was obtained.