Biochimica et BiophysicaActa, 767 (1984) 507-514 507 Elsevier BBA 41639 ELECTROPHOTOLUMINESCENCE AND THE ELECTRICAL PROPERTIES OF THE PHOTOSYNTHETIC MEMBRANE II. ELECTRIC FIELD-INDUCED ELECTRICAL BREAKDOWN OF THE PHOTOSYNTHETIC MEMBRANE AND ITS RECOVERY * DANIEL L. FARKAS, SHMUEL MALKIN and RAFI KORENSTEIN ** Departments of Biochemistry and Membrane Research, The Weizmann Institute of Science, Rehovot (Israel) (Received May 21st, 1984) Key words: Electrophotoluminescence; Luminescence; Thylakoid vesicle," Electric fieM effect; (Pea, spinach, lettuce chloro- plasO Preilluminated suspensions of swollen thylakoid vesicles ('blebs') were exposed to uni- and bipolar pairs of identical electric field pulses of variable duration, intensity and spacing. The resulting field-stimulated luminescence (electrophotoluminescence) was used as an intrinsic, voltage-sensitive optical probe to monitor electrical phenomena at the membrane level. The application of a pair of voltage pulses of opposite polarity made it possible to produce electric changes in the membrane by the first pulse and to analyse these effects by a second pulse of opposite polarity. It was found that the relative amplitudes of the two electrophoto- luminescence signals depended on the intensity of the applied electric field and on the time interval (t*) between the two pulses. When t* varied from 0.4 to 12 ms, the second stimulated luminescence signal was at first much smaller than the first one and then increased exponentially until the two signals were equal for t* >_ 3 ms. We analysed these differences between the two field-stimulated luminescence signals as a measure of the electrical breakdown of the membrane, induced during the first pulse. In this way a distinction between irreversible and reversible breakdown could be made with an estimation of the recovery kinetics of the reversible breakdown, which was found to be complete within 3 ms. Irreversible breakdown of the membrane was found to increase with lengthening the exposure time from 0.1 to 1.3 ms especially when applying high electric field of at least 2000 V/cm. Introduction The effect of high-intensity external electric fields on membrane conductance of cells, organelles and on artificial lipid bilayers has been considered in numerous publications [1-16 and reviews 17 and 18]. These studies demonstrate that * For part I, see Ref. 24. ** To whom correspondence should be addressed. Abbreviations: Tricine, N-[2-hydroxy-l,l-bis(hydroxymethyl) ethyl]glycine; EPL, electrophotoluminescence. membranes exposed to an electric field of strength exceeding a threshold value undergo electrical breakdown due to induced perforation, detected via a significant increase of membrane conductiv- ity. Both direct and indirect methods have been used to investigate this process. The direct meth- ods were based on electrical measurements of membrane conductance by macroscopic elec- trodes, in the case of black lipid bilayers, or by microelectrodes and electrofocusing Coulter coun- ters, in the case of whole cells [1-6]. The indirect methods (of nonelectrical nature) used to detect