Electrokinetic Membrane Processes in Relation to Properties of Excitable Tissues

An artificial system is studied consisting of salt solutions of different concentrations separated by a porous, "charged" membrane, through which a constant electric current is passed. Experiments on such systems demonstrate rhythmic variations of the transmembrane potential and the membrane resistance, which are concomitant with an oscillatory streaming of water solution across the membrane. The repetitive oscillations can be of a damped or undamped type dependent on the "stimulating" current density. A qualitative discussion of the mechanism of the oscillations is given. It centers around the periodic resistance changes in the membrane, which result from a complicated interplay between the driving forces present. The importance of electro-osmotic effects is emphasized. A few comparisons relating to possible electrophysiological implications are presented. In the metastable state of this membrane oscillator, "make" and "break" responses can be triggered by electric as well as by mechanical (pressure) "stimuli."