ACCESS RESISTANCE OF A SINGLE CONDUCTING MEMBRANE CHANNEL

We have considered the access resistance (AR) of a single conducting c hannel placed in a membrane bathed by an electrolyte. The classical ex pression for AR is due to Hall, who modeled the electrolyte as an ohmi c conducting homogeneous medium. This approach is discussed in the pre sent paper and it is shown that it is not valid in all cases, but depe nds on the ion concentration in solution and the ratio between solutio n and channel resistivities. To get a new expression for AR, we have c ombined the use of one-dimensional Nemst-Planck and Poisson (NPP) equa tions for the mouth of the channel and three-dimensional NPP equations for the outside solution. The influence of ion gradients and the chan nel itself on AR turns out to be considerable in diluted solutions (an d also in the case of small channels in any solution). This influence is weaker in concentrated solutions, for which AR is well described by Hall's expression. (C) 1998 Elsevier Science B.V.