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Biologic membranes display rectification of electrical current, as well as other properties, in many respects similar to precipitation membranes. The experiments reported here, performed in frog skin, show that these characteristics are dependent upon the presence of calcium. Upon elimination of calcium from the bathing solution, the property of electrical rectification is lost, the current-voltage relation assuming a linear form. Readministration of calcium brings about complete recovery of the rectification pattern. This behavior is analogous to chemical deconditioning of precipitation membranes. Our findings support the assumption that the binding of calcium in biologic membranes produces electrical effects characteristic of precipitation membranes.

Precipitation membranes, iike biological membranes, are specifically impermeable to certain ions. This property can easily be removed (deconditioning of the membrane) and restored again (reconditioning). The assumption is that special properties of the membrane are due to ion charges, adsorbed on precipitate layers. In this paper we study the deconditioning of the BaSO 4 precipitation membrane by an imposed electrical field. To achieve this electrical deconditioning, a threshold potential across the membrane has to be surpassed during a certain minimum of time. If this is done, the membrane potential of the conditioned precipitation membrane is lowered to the sum of the liquid junction potentials in the system in absence of an ion barrier. The rectification action of the membraneis lost, too. After switching off the imposed field, a spontaneous reconditioning takes place. The readjustment of both the membrane potential and the rectifying properties were followed. The first phase of reconditioning is obviously diffusion-controlled. All the results reported confirm the assumption stated above. The phenomena described can easily be explained as caused by the removal and the readjustment of adsorbed ions.BaSO4 membranes, as an example of precipitation membranes, have been studied in detail by one of us (P.H.-A.) for a number of years (for bibliography see Hirsch-Ayalon, 1973). They are formed spontaneously by diffusion-controlled precipitation within an inert supporting membrane, in our case by counter diffusion of Ba(OH)2 and HzSO 4 across a sheet of cellophane. The so-formed Ba(SO4) membranes are nearly ideally impermeable to Ba ++ and SO4-ions, as long as they are in the "conditioned" state, while, at the same time, they are permeable to other ions such as H +, OH-, K + and C1-(Hirsch-Ayalon, 1956).The following abbreviations are used throughout the text: Ag = the membrane potential, described by the equation below. A~t r = the intrinsic resting potential of the membrane. A~t m = the voltage drop across the membrane, due to an external electrical field. Agq = the time-dependent potential of the membrane after depolarization.

The behavior of precipitate‐membranes of BaSO4 in cellophane is discussed in terms of the formation process of the system and the known permeability to Ba++, SO=4 and to water components. It is shown that the available information leads to an interpretation in terms of an electrical bipolar model. The specific case of Ba(OH)2 and H2SO4 solutions separated by the above membrane is discussed in detail. The rectification effect and the non‐zero stationary currents observed are discussed in terms of the flows of H+, OH− and the flow of the chemical reaction of water formation. The logarithmic term derived for the voltage current relationship is shown to be directly linked with the depolarizing effect of water formation, and thus quantitatively related to the kinetic constants of water formation and dissociation.