Light-induced Potential Changes Research Articles

Kinetic photovoltage along semiconductor-water interfaces

External photo-stimuli on heterojunctions commonly induce an electric potential gradient across the interface therein, such as photovoltaic effect, giving rise to various present-day technical devices. In contrast, in-plane potential gradient along the interface has been rarely observed. Here we show that scanning a light beam can induce a persistent in-plane photoelectric voltage along, instead of across, silicon-water interfaces. It is attributed to the following movement of a charge packet in the vicinity of the silicon surface, whose formation is driven by the light-induced potential change across the capacitive interface and a high permittivity of water with large polarity. Other polar liquids and hydrogel on silicon also allow the generation of the in-plane photovoltage, which is, however, negligible for nonpolar liquids. Based on the finding, a portable silicon-hydrogel array has been constructed for detecting the shadow path of a moving Cubaris. Our study opens a window for silicon-based photoelectronics through introducing semiconductor-water interfaces.

Investigation of membrane potential changes in Nitellopsis obtusa cells induced by blue and red light stimulation

Light controls multiple physiological processes in plants. Membrane potential is widely used to report the early events as­sociated with changes in ion permeability, thus the effect of monochromatic light on bioelectrical parameters of Nitellopsis ob­tusa cells was examined. In this study blue, red and far-red light-induced membrane potential changes, light-induced photoelectrical reaction and membrane excitability were investigated using K’-anaesthesia method. All investigated lights cause the same bioelectrical events in Nitellopsis obtusa cells. It can be concluded that all photoreception systems exert their effects by first altering the permeability of the plasma membrane to ions and later ion channels perform signal-transducing functions in the complex array of mechanisms that determine plant physiology.

Light-Triggered Modulation of Cellular Electrical Activity by Ruthenium Diimine Nanoswitches

Ruthenium diimine complexes have previously been used to facilitate light-activated electron transfer in the study of redox metalloproteins. Excitation at 488 nm leads to a photoexcited state, in which the complex can either accept or donate an electron, respectively, in the presence of a soluble sacrificial reductant or oxidant. Here, we describe a novel application of these complexes in mediating light-induced changes in cellular electrical activity. We demonstrate that RubpyC17 ([Ru(bpy)(2)(bpy-C17)](2+), where bpy is 2,2'-bipyridine and bpy-C17 is 2,2'-4-heptadecyl-4'-methyl-bipyridine), readily incorporates into the plasma membrane of cells, as evidenced by membrane-confined luminescence. Excitable cells incubated in RubpyC17 and then illuminated at 488 nm in the presence of the reductant ascorbate undergo membrane depolarization leading to firing of action potentials. In contrast, the same experiment performed with the oxidant ferricyanide, instead of ascorbate, leads to hyperpolarization. These experiments suggest that illumination of membrane-associated RubpyC17 in the presence of ascorbate alters the cell membrane potential by increasing the negative charge on the outer face of the cell membrane capacitor, effectively depolarizing the cell membrane. We rule out two alternative explanations for light-induced membrane potential changes, using patch clamp experiments: (1) light-induced direct interaction of RubpyC17 with ion channels and (2) light-induced membrane perforation. We show that incorporation of RubpyC17 into the plasma membrane of neuroendocrine cells enables light-induced secretion as monitored by amperometry. While the present work is focused on ruthenium diimine complexes, the findings point more generally to broader application of other transition metal complexes to mediate light-induced biological changes.

Quantification of the electrochemical proton gradient and activation of ATP synthase in leaves

We have developed a new method to quantify the transmembrane electrochemical proton gradient present in chloroplasts of dark-adapted leaves. When a leaf is illuminated by a short pulse of intense light, we observed that the light-induced membrane potential changes, measured by the difference of absorption (520 nm–546 nm), reach a maximum value (~190 mV) determined by ion leaks that occur above a threshold level of the electrochemical proton gradient. After the light-pulse, the decay of the membrane potential follows a multiphasic kinetics. A marked slowdown of the rate of membrane potential decay occurs ~100 ms after the light-pulse, which has been previously interpreted as reflecting the switch from an activated to an inactivated state of the ATP synthase (Junge, W., Rumberg, B. and Schröder, H., Eur. J. Biochem. 14 (1970) 575–581). This transition occurs at ~110 mV, thereby providing a second reference level. On this basis, we have estimated the Δμ˜H+ level that pre-exists in the dark. Depending upon the physiological state of the leaf, this level varies from 40 to 70 mV. In the dark, the Δμ˜H+ collapses upon addition of inhibitors of the respiratory chain, thus showing that it results from the hydrolysis of ATP of mitochondrial origin. Illumination of the leaf for a period longer than several seconds induces a long-lived Δμ˜H+ increase (up to ~150 mV) that reflects the light-induced increase in ATP concentration. Following the illumination, Δμ˜H+ relaxes to its dark-adapted value according a multiphasic kinetics that is completed in more than 1 h. In mature leaf, the deactivation of the Benson–Calvin cycle follows similar kinetics as Δμ˜H+ decay, showing that its state of activation is mainly controlled by ATP concentration.

Cell physiological aspects of the plasma membrane electrogenic H+ pump.

This article deals with cell physiological aspects of the plasma membrane electrogenic proton (H+) pump and emphasizes the contribution of the giant algal cells of the Characeae in elucidating the mechanism of the pump. First, a history of the development of intracellular perfusion techniques in characean internodal cells is described, including preparation of tonoplast-free cells. Then, an outline of the hypothesis of the electrogenic H+ pump proposed by Kitasato is introduced, who prophesied the existence of an electric potential generated by an active H+ efflux. Subsequently, a history of finding ATP as the direct energy source of the electrogenic ion pump is presented. Quantitative agreement between the pump current and the ATP-dependent H+ efflux supports the notion that the ion carried by the electrogenic ion pump is H+. The role of the H+ pump in regulation of the cytosolic pH is discussed. Mechanisms of light-induced potential change through photosynthesis-controlled activation of the H+ pump are discussed in terms of changes in the levels of adenine nucleotides and in modulation of the Km value for the ATP of H+-ATPase. Recent progress in the molecular mechanism of the blue-light-induced activation of the H+-ATPase in guard cells is presented. However, there are cases where H+-ATPase activity is inhibited by blue light, indicating the flexibility of the control mechanisms of H+-ATPase activity. Finally, modulation of H+-pumping or H+-ATPase activities in response to environmental factors, such as anoxia, membrane excitation, osmotic and salt stresses, nutrient deficiencies and aluminum toxicity are described. Discussions are presented on the regulation of the electrogenic H+ pump.

CO2 provides an intermediate link in the red light response of guard cells.

Guard cells in intact leafs display light-induced membrane potential changes, which alter the direction of K+-transport across the plasma membrane (Roelfsema et al., 2001). A beam of blue light, but not red light, directed at the impaled guard cell triggers this response, while both light qualities induce opening of stomata. To gain insight into this apparent contradiction, we explored the possible interaction between red light and CO2. Guard cells in the intact plant were impaled with double-barrelled electrodes and illuminated with red light. Cells that were hyperpolarized in CO2-free air, depolarized after a switch to air with 700 micro l l(-1) CO2, in a reversible manner. As a result, K+-fluxes across the plasma membrane changed direction, to favour K+ extrusion and stomatal closure in the presence of CO2. Concurrent with the depolarization, an inward current across the plasma membrane appeared, most likely due to activation of anion channels. Guard cell responses to CO2 could be recorded in darkness as well as in red light. However, in darkness some cells spontaneously depolarized, these cells hyperpolarized again in red light. Here, red light was projected on a large area of the leaf and decreased the intracellular CO2 concentration by about 250 micro l l(-1), as measured with a miniature CO2 sensor placed in the substomatal cavity. We conclude, that in intact leaves the red light response of guard cells is mediated through a decrease of the intercellular CO2 concentration.

Imaging the surface potential of active purple membrane

AbstractBacteriorhodopsin, the light‐driven proton pumping protein in the purple membrane of Halobacterium salinarium, is known to be fully functional in various environments. Because of this, the protein's potential for technological application has been recognized. To investigate bacteriorhodopsin's light‐induced surface potential changes in humid air, we modified our commercial atomic force microscope to allow imaging at controlled humidities and toggling between defined lighting conditions. The purple membrane patches are prepared from solution onto freshly cleaved highly oriented pyrolytic graphite and imaged in the surface potential detection mode, also called Kelvin probe force microscopy, to identify their topography and surface potential in parallel. Precise tuning of the detection mechanism is crucial to allow imaging of the relatively small potential differences on the purple membrane (in the millivolt range). Our results show that the two orientations of the purple membrane can be identified by their surface potential. This is verified by high‐resolution topography images of the patches. Further experiments also show that, for the first time, it was possible to toggle the surface potential of the purple membrane patches by 3–5 mV when imaging the sample in dark or illuminated surrounding in humid air. Copyright © 2002 John Wiley & Sons, Ltd.

The Role of Light-Induced Membrane Potential Changes in Guttation in Gametophytes of Asplenium trichomanes

Gametophytes of the fern Asplenium trichomanes exhibit guttation when illuminated. Membrane potential changes evoked by light were measured in the presence of ion channel and proton pump inhibitors to elucidate the nature of the response and a possible link to guttation. Light-induced depolarization was suppressed by the anion channel inhibitors: anthracene-9-carboxylic acid and niflumic acid. Potassium channel blockers: TEA and Ba2+ caused an increase of the amplitude of light-induced membrane potential changes. Calcium channel inhibitors, La3*, Gd3+, diltiazem, nifedipine and verapamil had no significant effect on the membrane potential changes. Similarly, proton pump inhibitors, diethylstilbestrol and vanadate, had only minor effects on the response. A possible role of Cl~ and K+ fluxes in light-induced guttation is discussed.

Effects of Anion Channel Inhibitors on Light-Induced Potential Changes in the Liverwort Conocephalum conicum

The effect of three different anion channel inhibitors, namely (5-nitro-2-3-phenylpropyl-amino)benzoic acid (NPPB), Zn 2+ and anthracene-9-carboxylic acid (A-9-C) on the action potential in the liverwort Conocephalum conicum were tested. All three caused an increase of the excitability threshold and a decrease of action potential amplitudes. This confirms the involvement of anion channels in the action potentials in Conocephalum. In plants treated with 1 or 2 mM A-9-C but not with NPPB (50 or 100 //M) and Zn 2+ (100 or 500 //M), a light-induced transient depolarization occurred. In contrast to action potentials, the amplitude of this voltage transient depended on the light intensity and on the duration of preceding dark period. Also in contrast to action potentials, which are blocked by TEA, when applied together with A-9-C, TEA even increased the amplitudes of the light-induced voltage transients to up to 170 mV. The depolarization was obviously limited by the voltage-dependent opening of K + channels in the absence of TEA. The amplitude of the light-induced voltage transients (in the presence of TEA) increased in elevated CaCI2 concentrations pointing to a Ca 2+ permeability giving rise to the depolarization. However, none of the Ca 2+ channel blockers tested, La 3+ , Gd 3+ , nifedipine, verapamil or diltiazem, had an effect. The light-induced voltage transients in A-9-C treated plants are quite different from light- and electrically triggered action potentials but share some similarities with light-induced generator potentials.

Light-induced membrane potential changes of epidermal and mesophyll cells in growing leaves of Pisum sativum

Light transiently depolarizes the membrane of growing leaf cells. The ionic basis for changes in cell membrane electrical potentials in response to light has been determined separately for growing epidermal and mesophyll cells of the argenteum mutant of pea (Pisum sativum L.). In mesophyll cells light induces a large, transient depolarization that depends on the external Cl− concentration, is unaffected by changes in the external Ca2+ or K+ concentration, is stimulated by K+-channel blockers tetraethylammonium (TEA+) and Ba2+, and is inhibited by 3-(3′-4′-dichlorophenyl)-1,1-dimethylurea (DCMU). In isolated epidermal tissue, light induces a small, transient depolarization followed by a hyperpolarization of the membrane potential. The depolarization is enhanced by increasing the external Ca2+ concentration and by addition of Ba2+, and is not sensitive to DCMU. Epidermal cells in contact with mesophyll display a depolarization resembling the response of the underlying mesophyll cells. The light-induced depolarization in mesophyll cells seems to be mediated by an increased efflux of Cl− while the membrane-potential changes in epidermal strips reflect changes in the fluxes of Ca2+ and in the activity of the proton-pumping ATPase.

Photosensory transduction in ciliates. I. An analysis of light-induced electrical and motile responses in Stentor coeruleus.

Light-induced membrane potential changes and motile responses have been studied in Stentor cells with intracellular microelectrodes and video microscopy, respectively. Intracellular microelectrode recordings showed that step-up increase in light intensity induced an electrical membrane response which consisted of an initial membrane depolarization (photoreceptor potential) followed by an action potential and maintaining phase of depolarization (afterdepolarization). The amplitude of the receptor potential is dependent on the intensity of light stimulus and the action potential appears with a lag period (latency) after the onset of light stimulus. The extent of the membrane afterdepolarization is dependent on the intensity and duration of stimulus used. A close time correlation has been established between the latency for the action potential and the onset of ciliary reversal (stop response). A time correlation was also observed between the duration of the membrane afterdepolarization and the duration of backward swimming. The action spectrum for the photoreceptor potential amplitude of Stentor resembled the action spectra for the latency of ciliary reversal and the photoresponsiveness, indicating that the photomovement response and membrane potential changes are coupled through the same photosensor system. A hypothesis on the photosensory transduction chain in Stentor is discussed according to which the photoreceptors and the ciliary apparatus is mediated by the membrane potential changes.

Analysis of Rapid Light-Induced Potential Change in Cells of Chara corallina

Analysis of Rapid Light-Induced Potential Change in Cells of Chara corallina

Evidence for Direct Involvement of Functional Membranes of Chloroplasts in the Rapid Photoelectrical Response of Plasmatic Membranes through Membrane Continuities in Nitellopsis obtusa

After inhibition of conventional light-induced potential changes of the plasmatic membranes of N. obtusa with the inhibitor of photophosphorylation tentoxin, a new photoelectrical reaction appears, which is analogous to the well-known photoelectrical response of a single chloroplast. The new photoelectrical reaction is inhibited by DCMU and restored by PMS, what indicates its photosynthetic origin. It is supposed that the rapid photoelectrical response measured between the streaming cytoplasm and the external medium is electrically coupled to the photoelectrical response of the chloroplast functional membranes by membrane continuities between thylakoid membranes and chloroplast envelope on the one hand, and the chloroplast envelope and the chlorolemma on the other hand. Thus the results presented provide further evidence for the existence of the chlorolemma, the membrane separating the immobile chloroplast layer from the streaming cytoplasm (GYENES and SAXENA 1985a).

Photoelectric signals generated by bovine rod outer segment disk membranes attached to a lecithin bilayer

Purified bovine rod outer segment disk membranes were attached to a lecithin bilayer membrane. After photoexcitation with a 500-nm flash delivered by a dye laser, a negative photovoltage was observed on the bilayer under normal ionic strengths (100 mM KCl), which had a rise phase of 1-3 ms at 20 degrees C. The photoresponse was obviously due to bleaching of rhodopsin as it decreased for successive flashes of light. It originated most probably during the metarhodopsin-I metarhodopsin-II (meta-I-II) transition of rhodopsin because it was pH dependent at 2 degrees C but not at 20 degrees C. At 10 mM KCl, i.e., under hypotonic conditions, a positive photovoltage with slower kinetics than at high salt was observed. As the disk membranes were merely attached to the bilayer membrane, the photovoltage was apparently due to a light-induced transmembrane potential change in the disk membranes. Possible electrogenic mechanisms underlying the photosignal will be discussed.

Investigation of electrophysiological responses of Neurospora crassa to blue light

The influence of light in a spectrum range of 350–500 nm 20 W m-2 (20,000 erg · cm-2 · s-1) has been studied in the mycelial cells of Neurospora crassa. Light-induced input resistance and membrane potential changes can be measured by means of intracellular microelectrodes. The value of the input resistance reached maximum after a 2–5 min illumination. The maximum hyperpolarization of the cell membrane reaching 30–40 mV was observed after 20–25 min illumination, when the input resistance values did not differ significantly in the illuminated and non-illuminated cells.

Bacterial rhodopsins monitored with fluorescent dyes in vesicles and in vivo.

Three retinal-containing pigments have been detected in Halobacterium halobium membranes: bacteriorhodopsin (bR), halorhodopsin (hR), and slow-cycling rhodopsin (sR). The first two hyperpolarize the cell membrane by electrogenic transport of H+ and Cl-, respectively. The third pigment, sR, may be a photosensory receptor since mutants lacking bR and hR retain their retinal-dependent phototaxis responses. We monitored light-induced changes in fluorescence of several voltage-sensitive dyes in cells and membrane vesicles. Red light-induced potential changes generated by bR and hR were similar to signals described previously. Signals generated by hR could be identified using four criteria: wavelength dependence, Cl- dependence, shunting by valinomycin and K+, and the absence of these signals in hR-deficient mutants. The absence (detection limit approximately 0.5 mV) of hyperpolarization signals in bR-hR-sR+ vesicles and cells shows that sR photochemical reactions are nonelectrogenic. Two signals independent of bR and hR were measured: blue light caused a decrease and red light an increase in dye fluorescence. Both signals appear to derive from sR on the basis of their retinal-dependence and action spectra. In a retinal-deficient mutant strain (Flx3R), both sR signals appeared after addition of all-trans retinal. In this strain retinal also restores phototaxis sensitivity within the same time scale. The retinal concentration dependence for all four parameters monitored--the attractant (red) and repellent (blue) phototaxis, and the red light and blue light-induced fluorescence signals--is the same. This correlation is consistent with the hypothesis that both attractant and repellent responses are mediated by sR, as suggested by Bogomolni and Spudich (Proc. Natl. Acad. Sci. USA. 79:6250-6254 (1982)).

Light-dependent ion influx into toad photoreceptors.

To measure the influx of Na+ and other ions through the light-dependent permeability of photoreceptors, we superfused the isolated retina of the toad, Bufo marinus, with a low-Ca2+ (10(-8) M), low-Cl- Ringer's solution containing 0.5 mM ouabain. Under these conditions, the membrane potential of the rod is near zero and there is no light-induced potential change either in the rod or in more proximal neurons. The photoreceptors, however, continue to show a light-dependent increase in membrane resistance, which indicates that the light-sensitive channels still close with illumination. Dark-adapted retinas show a larger 22Na+ accumulation than do light-adapted retinas. The extra accumulation of 22Na+ into dark-adapted retinas can be removed if the retinas are washed in darkness with low-Ca2+ Ringer's solutions, or if the ionophore gramicidin D is present in the perfusate. The additional accumulation in dark retinas corresponds to a flux of at least 10(9) Na+ per receptor per second, which is close to the value of the photoreceptor dark current. The light-dependent uptake of 22Na+ can be prevented by exposing the retinas to Ca2+ during the incubation period, but is restored if the phosphodiesterase inhibitor IBMX is added to the perfusate. A significant light-dependent ion accumulation can be observed for the cations K+, Rb+, Cs+, and Tl+, in addition to Na+, but not for methylamine, choline, or tetraethylammonium.

Salt dependence of the electrical potential at the photosynthetic membrane in steady-state light and its structural consequence

(1) The change in potential difference across the functional membrane of photosynthesis has been measured as a function of KCI concentration of the suspending medium under saturating, continuous illumination. The measurements have been carried out through the potential-indicating electrochromic absorption changes. Between 1 and 100 mM KCI, a decrease from 80 to about 0 mV was found. The salt dependence can be described by a Donnan model which is based on buffer groups located within the inner space of the system. A Gouy-Chapman model based on buffer groups located at the plane of the inner membrane surface does not fit the data of the measurements. The strong salt dependence may explain apparent discrepancies between the values of the light-induced potential changes reported in the literature. (2) Measurements of the membrane conductance of the ionophore, nonactin-K +, as a function of the internal proton concentration have been carried out. Also, in this case, the results can be explained by a Donnan model. The consequence of both results, i.e., distribution of the buffer groups of thylakoids within the inner space, is possibly realized by membrane-bound proteins which project up to about 20 nm into the inner thylakoid space, as well as through unbound proteins (see Fig. 7). Inter alia, the carboxyl groups of aspartic and glutamic acids of these proteins may be the effective buffer groups. Plastocyanin may also contribute to this effect in a minor way.

Lateral transport of energy along the coupling membranes of cyanobacteria.

The light-induced electric potential changes brought about local illumination of trichomes of cyanobacteria Phormidium uncinatum have been studied by means of extracellular electrodes. Responses of several electrodes located at various distances from the illuminated area of the trichome were monitored simultaneously. They turned out to be similar in shape: a rapid increase to the maximum value was followed by a slow decay toward a nonzero residual level. The results offer strong evidence in favor of power transmission along the trichome. The computerized experimental data lend support to the notion of a unified system of coupling membranes acting as a passive cable for electrical propagation, the cable parameters being tau C = 440 sec cm-2 and gamma = 0.07 cm.

Demonstration of Voltage Dependency of Light-induced Potential Change in <italic>Chara</italic>

Demonstration of Voltage Dependency of Light-induced Potential Change in <italic>Chara</italic>