Dielectric breakdown in the membranes of Valonia utricularis. The role of energy dissipation.

The electrical properties of the membranes of Valonia utricularis were investigated using intracellular electrodes. Using short (0.5-1.0 ms) current pulses it was found that at a critical membrane potential difference of 0.85 V there was a large and discontinuous decrease in the membrane impedance and the slope resistance beyond this potential was virtually zero. The electrical breakdown of the membranes did not lead to global damage of the cells and after a resealing time of approx. 5 s could be repeated with identical results. Experiments with long current pulses and long bursts of pulses repeated at 1 kHz are described which show that the electrical breakdown is not due to thermal damage arising from localized heating in the membrane. Thus a dissipation of some 10-3-10-5 times the energy normally dissipated during the onset of breakdown did not lead to breakdown itself unless the critical membrane potential was exceeded. The results also show that punch-through and avalanche ionization are not likely to be important in the breakdown mechanism. The results are consistent, however, with there being a critical instability in the electro-mechanical stresses set up in the membrane at large electric field strengths.