Oscillations of Membrane Potential across a Polypeptide Membrane, Induced by an Electrical Current

Oscillation of membrane potential across a tri-block copolypeptide membrane composed of (Glu)x-(Leu)y-(Glu)x(x = 0.18 and y = 0.64) was observed under an electrical current, when the membrane was placed between equimolar aqueous salt solutions. The amplitude of the oscillation was influenced by the type of cation and anion in the external salt solution, and the amplitude was in the sequence: K+>Na+>Cs+>Ca2+and Cl−>Br−. The frequencies of the oscillations were in the range 0.1 to 5 Hz, and were also slightly influenced by the type of cation and anion.