Electrophotoluminescence and the electrical properties of the photosynthetic membrane. I. Initial kinetics and the charging capacitance of the membrane

Abstract

Preilluminated chloroplast membranes, and particularly hypotonically swollen vesicles (blebs), give rise to a strong characteristic luminescence (electrophotoluminescence, EPL; Ellenson and Sauer, 1976, Photochem. Photobiol., 23:113-123; Arnold and Azzi, 1971, Photochem. Photobiol., 14:233-240) during the application of a strong external electric field. A detailed kinetic study of EPL was carried out and the initial kinetics from the field onset are reported here. The fast rise time (less than 0.2 mus) of the applied external electric field together with a high instrumental time resolution allowed the observation of a characteristic delay (lag time) between the field onset and the appearance of the induced emission. The lag time decreased with increase in the applied field strength and/or the conductivity of the suspension and is interpreted to be a consequence of (a) the necessity to reach a threshold electrical potential difference in the bleb membrane, below which no emission can be triggered, and (b) the finite time required to attain such a transmembranal field during the charging process of the membrane. A quantitative analysis, connecting the lag time, the controllable experimental parameters, and the membrane electrical characteristics is presented. Its verification was carried out in both size-selected and heterogeneous bleb populations. In the latter, experiments were consistent with the assumption that the lag time reflects the charging of the largest blebs. The results indicate (a) the possibility of directly measuring the specific membrane capacitance, yielding an estimate of Cm = 1.2 +/- 0.3 microF/cm2 (the precision being particle size-homogeneity dependent); (b) A minimal transmembranal potential difference (of approximately 240 mV) is necessary to induce electrophotoluminescence; and (c) the lag duration depends on the time elapsed between the preillumination and the external field application. Correlated with the study of ionophore effects on the lag time, this suggests additivity of the light- and field-induced transmembrane potentials in attaining the threshold for emission.

A novel method for measuring membrane conductance changes by a voltage‐sensitive optical probe

“…This phenomenon was observed upon addition of gramicidin molecules to a suspension of thylakoids [6,8]. This fact can be used to make indirect measurements of changes in the membrane conductance by measuring the change in the EPL signal, provided we give a quantitative measure to the attenuation of the signal.…”

“…It has previously been shown [6,8] that the EPL amplitude is sensitive to changes in membrane conductance. The attenuation of the EPL due to the increase in membrane conductivity results from the decrease in the electrical field induced in the membrane.…”

“…The attenuation of the EPL due to the increase in membrane conductivity results from the decrease in the electrical field induced in the membrane. The stationary local electric field (Em) induced in a vesicular membrane upon exposure to externally applied electric field (E,,) was previously shown [6] to be:…”

“…The ionophores were added from concentrated ethanolic solutions (1 mM) while continuously stirring the vesicle suspension. The experimental set-up for electrophotoluminescence measurements was described elsewhere [6]. The experiment was initiated by a preillumination, for 120 ms with a light projector.…”

Influence of Cellular Properties on the Electric Field Distribution Around a Single Cell

“…Among these, Farkas et al [17] provided a partial solution for the transmembrane electric field in a spherical cell model. Jerry et al [18] solved the electric distribution inside and outside of a cell with a prolate spheroidal shape.…”