Light-induced Potential Research Articles

Light-induced membrane potential and pH gradient in Halobacterium halobium envelope vesicles.

Illumination of envelope vesicles prepared from Halobacterium halobium cells causes translocation of protons from inside to outside, due to the light-induced cycling of bacteriorhodopsin. This process results in a pH gradient across the membranes, an electrical potential, and the movements of K+ and Na+. The electrical potential was estimated by following the fluorescence of a cyanine dye, 3,3'-dipentyloxadicarbocyanine. Illumination of H. halobium vesicles resulted in a rapid, reversible decrease of the dye fluorescence, by as much as 35%. This effect was not seen in nonvesicular patches of purple membrane. Observation of maximal fluorescence decreases upon ilumination of vesicles required an optimal dye/membrane protein ratio. The pH optimum for the lightinduced fluorescence decrease was 6.0. The decrease was linear with actinic light intensity up to about 4 X 10(5) ergs cn-2 s-1. Valinomycin, gramicidin, and triphenylmethylphosphonium ion all abolished the fluorescence changes. However, the light-induced pH change was enhanced by these agents. Conversely, buffered vesicles showed no pH change but gave the same or larger fluorescence changes. Thus, we have identified the fluorescence decrease with a light-induced membrane potential, inside negative. By using valinomycin-K+-induced membrane potentials, we calibrated the fluorescence decrease with calculated Nernst diffusion potentials. We found a linear dependence between potential and fluorescence decrease of 3 mV/%, up to 90 mV. When the envelope vesicles were illuminated, the total proton-motive force generated was dependent on the presence of Na+ and K+ and their concentration gradients across the membrane. In general, K+ appeared to be more permeable than Na+ and, thus, permitted development of greater pH gradients and lower electrical potentials. By calculating the total proton-motive force from the sum of the pH and potential terms, we found that the vesicles can produce proton-motive forces near--200 mV.

Photo-responsive membranes : I. Light-induced potential changes across membranes incorporating a photochromic compound

A photo-responsive membrane has been prepared by casting an acetone solution of a spiropyran compound, phosphatidyl choline, and acetyl cellulose. Since the membrane showed excellent transparency in either the dry or wet state, absorption spectra of bound spiropyran were easily obtained. The membrane-bound spiropyran exhibited normal photochromism: a colored form under UV irradiation and a colorless form under visible irradiation p]The potential difference across the membrane was drastically changed by switching from visible light to UV light irradiation. This light-induced membrane potential change was reversible and was synchronized with a change in absorbance of the membrane-bound spiropyran at 533 nm. A change of membrane charge density associated with the photoisomerization of spiropyran is thought to cause this dynamic photo-response in membrane potential

Delayed Fluorescence, the Carotenoid Shift and the Light-Induced Membrane Potential

Delayed Fluorescence, the Carotenoid Shift and the Light-Induced Membrane Potential

Shifts of bacteriochlorophyll and carotenoid absorption bands linked to cytochrome c-555 photooxidation in Chromatium

Shifts in the absorption bands of bacteriochlorophyll and carotenoids in Chromatium vinosum chromatophores were measured after short actinic flashes, under various conditions. The amplitude of the bacteriochlorophyll band shift correlated well with the amount of cytochrome c-555 that was oxidized by P 870 + after a flash. No bacteriochlorophyll band shift appeared to accompany the photooxidation of P 870 itself, nor the oxidation of cytochrome c-552 by P 870 +. The carotenoid band shift also correlated with cytochrome c-555 photooxidation, although a comparatively small carotenoid shift did occur at high redox potentials that permitted only P 870 oxidation. The results explain earlier observations on infrared absorbance changes that had suggested the existence of two different photochemical systems in Chromatium. A single photochemical system accounts for all of the absorbance changes. Previous work has shown that the photooxidations of P 870 and cytochrome c-555 cause similar changes in the electrical charge on the chromatophore membrane. The specific association of the band shifts with cytochrome c-555 photooxidation therefore argues against interpretations of the band shifts based on a light-induced membrane potential.

A method of estimating the magnitude of the light-induced electrical potential across the thylakoid membranes

A method of estimating the magnitude of the light-induced electrical potential across the thylakoid membranes

Effects of temperature change on the catfish S-potentials

Haблюдaлocь дeйcтвиe измeнeния тeмпepaтypы нa ypoвeнь пocтoяннoгo (тeмнoвoгo) пoтeнциaпa и нa вызвaнный cвeтoм пoтeнциaл ( S-пoтeнциaл) — S oблacти или гopизoнтaльных клeтoк coмa. Bpeмя пoдьeмa и зaтyхaния S-пoтeнциaлa oкaзaлocь бoлee хyвcтвитeльным к измeнeниьм тeмпepaтypы,в тo вpeмя кaк ypoвeнь пocтoьннoгo пoтeнциaлa oхeнь мaлo измeньлcь пpи измeнeнии тeмпepaтypы пpeпapaтa в пpeдeлaх oт 5 дo, пpиблизитeльнo, 30°. Xoтя тeмпepaтypныe измeнeния дaвaли зaмeтныe измeнeниь в фopмe вoлны S-пoтeнциaлoв, cooтвeтcтвиe oтнoшeниь aмплитyды к интeнcивнocти лoгиcтих ecкoй фyнкции бы eдocт aтoхнo хopoшим oт 7° пpимepнo дo 30°. Oднaкo, нaклoн кpивoй cтa нoвилcь oлмeнкpyтым, кoгдa тeмпepaтypa пpeпapaтa бялa нижe 7°.

Lateral spread of light-induced potentials along different cell layers in the teleost retina

By displacing a spot of white light (0.25 mm in dia.), in steps of 0.25 mm along a straight line over the receptor surface, the extent of the lateral spread of light-induced potential recorded intracellularly and the related spike discharges were investigated in the isolated retina of fishes ( Gerridae, Centropomidae and Mugilidae). Hyperpolarizing S-potentials were found to spread laterally along each layer of horizontal cells and of a class of amacrine cells. The S-potential amplitude was maximal at the center of the light spot, and decayed to one half of its maximum when the light spot was displaced 0.5 to 1.5 mm away from the recording point; differences in the half decay distance along different horizontal and amacrine cell layers were statistically significant. In the inner plexiform layer, various types of light-induced (sustained or on-off transient) potentials were recorded intracellularly. Although some of these sustained potentials were C-type S-potentials, the others were assumed to arise from spike-producing cells. The lateral distribution of these potentials varied widely from cell to cell, and some of the sustained potentials showed polarity reversal with distance, from the central hyperpolarizing to the peripheral depolarizing response, or vice versa. The spatial changes observed in spike discharge pattern were closely related to the changes in the sustained potentials exhibiting the polarity reversal or in the depolarizing on-off transients.

Schnelle photoelektrische Effekte der Alge Acetabularia

In the Alga Acetabularia intense light flashes produce transient depolarizing potentials which can be recorded intracellularly with 3 molar KCl glassmicroelectrodes. This rapid photoelectric effect has a latency of not more than 40 µsec. Spectral measurement showed a maximal sensitivity near 540 mµ. There is a second depolarization in the dark period after the flash. Lowering the temperature increases the amplitude of the fast depolarization and decreases the amplitude of the dark depolarization. Presumably the pigment and generator of the fast light-induced potential are associated with the cell membrane.