Polarization Studies in Tissue Models. ∗

Abstract

It is known that the electric resistance of animal tissues, contrary to that of solutions, is not determined by the law of Ohm alone. 1 This has been explained as consequence of polarization caused by semipermeable cell membranes at cell interfaces. The degree of polarization and, therefore, of the permeability can be measured by the capacitance or inductance needed to obtain a sharp minimum on the Wheatstone bridge. As further manifestation of polarization, the resistance of tissues decreases with the increasing frequency of the alternating current. While other authors worked mostly with methods based on the first phenomena, we used the difference in conductivity at high and low frequencies as measure of membrane polarization and permeability. In order to elucidate to some degree the chemical and colloid-chemical conditions underlying the polarization and permeability phenomena, different artificial membranes with various constituents were used.

A Wheatstone bridge was employed. Alternating currents of various frequencies (560 to 6890 cycles) were provided by an oscillator built according to the description of Jones and Joseph, 2 in combination with an amplifier.† The difference between the conductance at highest and lowest frequency was expressed in percentage of the conductivity at low frequency. This value will be called Δ in this paper. In order to obtain a sharp minimum, variable capacities (up to 0.5 M. F.) were employed. The conductance vessel consisted of 3 glass cells, the outer cells contained electrodes of platinum wire gauze covered with black of platinum. Their surface was 3.8 cm. 2 , the distance was 21 mm. Between the outer cells and the middle cell one or 2 membranes could be placed. The apparatus was filled with KCl solutions, whose concentration varied depending on the resistance of the membrane. (.01-1 n solutions). The method was first checked on frog's skins which gave a Δ of 23% (high frequency 6890 cycles, low frequency 560 cycles).