Reversible electrical breakdown of swollen thylakoid membrane vesicles. A study by electrophotoluminescence

Exposure of pre-illuminated swollen thylakoid vesicles to external electric fields caused stimulation of delayed luminescence of several orders of magnitude. The application of intense bipolar voltage pulses to a suspension of thylakoid vesicles resulted in two emission signals. The relative amplitude of the two emission signals depended on the intensity of the applied electric field and on the time-spacing (t^*) between the two pulses. The ratio between the emission produced by the second and the first pulse increased from {reversed tilde equals} 0.5 (for t* {reversed tilde equals} 0.4 ms) until it reached a value of unity (for t* ≥ 5 ms). It is suggested that the decreased amplitude of the second pulse reflects electrical breakdown of the membrane. The increase of the ratio between the second and the first pulse is suggested to reflect the kinetics of the resealing process. By a combination of phosphoroscope experiments with a.c. electric fields we were able to achieve a situation where on application of a long series of a.c. voltage pulses, the sample was identical for each field pulse with respect to the pool size of precursors available for delayed luminescence. Under these conditions, the main difference was always between the first and the second emission signals, suggesting electrical breakdown of the membrane by the first voltage pulse. It was shown that breakdown was more intense the higher the applied electric field. The angular dependence of the induced local field in the membrane could be detected via measurement of the polarization of the stimulated emission. A lower value for the polarization ratio was obtained for the second pulse as compared with the first one. This has been attributed to disorientation of the emittors at the areas where electroperforation takes place and to the decrease in the local field in the same areas.