[Uniform polarization of fibers and syncytial structures by extracellular electrodes]

The method is described which enables to measure the voltage-current relations of the membrane of fibres and of syncytial structures by means of the current passed through the extracellular electrodes. The method is based on such a distribution of extracellular resistances that the polarization of the membrane was uniform on a large area. For this purpose the extracellular longitudinal gradient of potential had to increase linearly as a function of distance from one of the edges of the preparation. Such a distribution of potentials was achieved by passing current along the conducting agar-layer, the thickness of which decreased with distance from the edge. The length of the agar-layer where the longitudinal potential gradient increased must be large in comparison with the space constant. It is shown that in the zone where polarization is uniform the density of the current crossing the membrane is proportional to the current passed through the preparation independently on the membrane resistance. The method was applied for measuring the voltage-current relations of the horizontal cell membrane in the fish retina.