On the steady-state electrical potential difference across the thylakoid membranes of chloroplasts in illuminated plant cells

The potential difference across the thylakoid membranes under steady-state saturating light conditions, measured with microcapillary glass electrodes, was found to be small as compared to the potential initially generated at the onset of illumination. This result is discussed to be in agreement with quantitative estimates on the approximate magnitudes of the potential generating electron flux through the photo-synthetic electron transport chain and of the potential dissipating ion fluxes across the thylakoid membrane under steady-state conditions. It is concluded that a pH gradient of approx. 3–3.4 units is built up in the light across the membrane. The negative diffusion potential associated with this gradient is suggested to cause the transient negative potential observed in the dark after illumination.     

On the steady-state electrical potential difference across the thylakoid membranes of chloroplasts in illuminated plant cells.

The potential defference across the thyladoid membranes under steady-state saturating light conditions, measured with microcapillary glass electrodes, was found to be small as compared to the potential initially generated at the onset of illunimation. This result is discussed to be in agreement with quantitative estimates on the approximate magnitudes of the potential generating electron flux through the photo-synthetic electron transport chain and of the potential dissipating ion fluxes across the thylakoid membrane under steady-state conditions. It is concluded that a pH gradient of approx. 3-3.4 units is built up in the light across the membrane. The negative diffusion potential associated with this gradient is suggested to cause the transient negative potential observed in the dark after illumination.     

On the mechanism of generation of electrical potential differences in cell biomembranes]

A statistical model of active ion transport in biomembranes was developed. The model makes it possible to calculate both the value of membrane potential phi zero and the rate of ion concentrations inside and outside the cell. These values depend on the difference of chemical potentials of the ATP-ADP system and the permeability of the biomembrane for ions being transported. The calculated phi zero value approximately 200-250 mV is consistent with the data on proton pumps.     

Spontaneous oscillation of electrical potential across organic liquid membranes

An artificial membrane was studied consisting of an oil layer, nitrobenzene containing picric acid, imposed between two aqueous phases, one of which contained 5 mM hexadecyltrimethylammonium bromide (CTAB) and 5% ethanol. It was found that this system shows rhythmic and sustained oscillation of the electrical potential within the range 150–300 mV with an interval of 2–3 min. In the absence of CTAB or ethanol, no oscillation was observed. It is indicated that in this experiment the concentrations of the solutes are far-from-equilibrium, i.e., the hydrophilic substance, picric acid, was dissolved in the organic phase and the hydrophobic substance. CTAB, was dissolved in the aqueous phase. In addition, the presence of an unstirred layer was suggested to be essential for generating such electrical oscillations.     

On the extent of the electrical potential across the thylakoid membrane induced by continuous light in Chlorella cells

The extent of the electrical potential Δ?_ss across the thylakoid membrane of Chlorella cells was estimated under steady state conditions. This has been achieved by comparing the absorption change which occurs after continuous light is switched off with a calibrated field indicating absorption change induced by flash light. Under saturating light conditions Δ?_ss is in the order of 100 mV.     

Measurements of electrical potential differences across yeast plasma membranes with microelectrodes are consistent with values from steady-state distribution of tetraphenylphosphonium inPichia humboldtii

Summary Electrical potential differences across the plasma membrane () of the yeastPichia humboldtii were measured with microelectrodes (filled with 0.1m KCl) inserted into cells immobilized in microfunnels. The registered signals were reproducible and stable for several minutes. On attainment of stable reading for the specific membrane resistanceR _sp was determined by applying square-current pulses to the preparation. Both andR _sp were pH dependent and displayed equal but opposite deflection, reaching its maximal value of –88±9 mV (n=13) andR _sp its minimal value of 10 k·cm² (maximal conductance) at pH 6.5. Uncouplers and the polyene antibiotic nystatin depolarized the cells, decreasing to –21±15 mV (n=10) with concomitant decrease ofR _sp. Comparison of values from microelectrode measurements with those calculated from the steady-state distribution of tetraphenylphosphonium ions agreed within 10 mV under all physiological conditions tested, except at pH values above 7.0. During microelectrode insertion transient voltage signals (a few msec long) were detected by means of an oscilloscope. These voltage signals were superimposed on the stable recordings described above. These short voltage signals disappeared in uncoupled cells. The closely related values obtained by two independent methods (direct measurements with microelectrodes and calculation from steady-state distribution of a lipophilic cation) provide evidence that these values reffect the true membrane potential of intact cells.     

Studies on the electrical potential profile across rabbit ileum. Effects of sugars and amino acids on transmural and transmucosal electrical potential differences

When isolated strips of mucosal rabbit ileum are bathed by physiological electrolyte solution the electrical potential difference (PD) across the brush border (ψ_mc) averages 36 mv, cell interior negative. Rapid replacement of Na in the mucosal solution with less permeant cations, Tris or choline, results in an immediate hyperpolarization of ψ_mc. Conversely, replacement of choline in the mucosal solution with Na results in an abrupt depolarization of ψ_mc. These findings indicate that Na contributes to the conductance across the brush border. The presence of actively transported sugars or amino acids in the mucosal solution brings about a marked depolarization of ψ_mc and a smaller increase in the transmural PD (Δψ_ms). It appears that the Na influx that is coupled to the influxes of amino acids and sugars is electrogenic and responsible for the depolarization of ψ_mc. Under control conditions Δψ_ms can be attributed to the depolarization of ψ_mc together with the presence of a low resistance transepithelial shunt, possibly the lateral intercellular spaces. However, quantitatively similar effects of amino acids on ψ_mc are also seen in tissues poisoned with metabolic inhibitors or ouabain. Under these conditions Δψ_mc is much smaller than under control conditions. Thus, the depolarization of ψ_mc might not account for the entire Δψ_ms, observed in nonpoisoned tissue. An additional electromotive force which is directly coupled to metabolic processes might contribute to the normal Δψ_ms.     

Rotation of cells in an alternating electric field theory and experimental proof

Summary Protoplasts ofAvena sativa rotate in an alternating electric field provided that at least two cells are located close to each other. An optimum frequency range (20 to 30 kHz) exists where rotation of all cells exposed to the field is observed. Below and above this frequency range, rotation of some cells is only occasionally observed. The angular velocity of rotation depends on the square of the electric field strength. At field strengths above the value leading to electrical breakdown of the cell membrane, rotation is no longer observed due to deterioration of the cells. The absolute value of the angular velocity of rotation at a given field strength depends on the arrangement of the cells in the electric field. A maximum value is obtained if the angle between the field direction and the line connecting the two cells is 45^o. With increasing distance between the two cells the rotation speed decreases. Furthermore, if two cells of different radii are positioned close to each other the cell with the smaller radius will rotate with a higher speed than the larger one. Rotation of cells in an alternating electric field is described theoretically by interaction between induced dipoles is adjacent cells. The optimum frequency range for rotation is related to the relaxation of the polarization process in the cell. The quadratic dependence of the angular velocity of rotation on the field strength results from the fact that the torque is the product of the external field and the induced dipole moment which is itself proportional to the external field. The theoretical and experimental results may be relevant for cyclosis (rotational streaming of cytoplasm) in living cells.     

The theory of the frequency response of ellipsoidal biological cells in rotating electrical fields

In this paper we have presented in as compact a form as possible the theoretical formalism that is needed to predict the frequency response of a biological cell of arbitrary ellipsoidal shape to a frequency dependant rotating external field. The formalism is much more complicated than that for a spherical or cylindrical cell where the radial vector is always parallel to the surface normal at each point of the surface. In addition to providing the theory we have demonstrated that the spin rate and its frequency dependance is very intimately related to the electrical properties of the cell interior and to that of the suspending fluid. It is possible to probe these properties of the cell and its environment by utilizing this technique. This aspect has been demonstrated by examining rotational changes as a function of the conductivity of both the cell interior and its suspending liquid. We also have shown, by considering a very simple model for the cell and the two dielectric constants, that the frequency spectrum is shape dependant. All our calculations have been carried out for "lossy" systems with frictional dissipation where energy minimization methods are no longer applicable. The invariant form of the Poynting vector forms the basis of the method.     

On the mechanics of viscous bodies and elongation in ellipsoidal cells

After deriving some auxiliary equations for the average elongation of a viscous body under the action of forces derived from a potential, the diffusion problem for an ellipsoidal cell with a constant rate of reaction is solved for the case of an infinite permeability. The equation of elongation of such a cell under the influence of diffusion forces is derived, and compared with the, approximate expression obtained by N. Rashevsky for any kind of oblong cell. The two equations are in fair agreement. Effects of constant and variable surface tension are studied.     

Methods of measuring the transmembrane electrical potential in cells

The methods of intracellular microelectrodes, penetrating ions and potential-sensitive fluorescent probes are considered for their possibility to be used for quantitative estimation of transmembrane electrical potentials (TMP) of small cells (mainly through the example of lymphocytes). The following fluorescent methods are described in detail: separate measurement of two TMP components--potentials on the plasma and mitochondrial membranes of a cell; recording of individual differences of cells according to the TMP value. It is supposed that heterogeneity of cells by the TMP value (in particular, the presence of depolarized cells) may be responsible for errors and divergences of the TMP mean values measured by different methods.     

外加稳恒直流电场对兔腹主动脉周围电势差的影响

目的:观察外加稳恒直流电场对兔腹主动脉周围电势差的影响.方法:在兔腹主动脉两侧腰大肌埋置刺激电极,在血管外膜、血管内外膜间安置测量电极,给予稳恒直流电场刺激,电场强度采用3V或4V,记录电场刺激前后血管周围电势差的变化情况.结果:①通电后即刻,血管周围电势差与通电前相比无变化(P>0.05).②通电后30min,血管外膜间和血管内外膜间电势差均明显增加,4V组增加更为明显.③断电后30min,两外膜间电势差基本恢复至通电前水平,而血管内外膜间电势差仍高于通电前,两刺激电极间仍有较高电势差存在.结论:将铂电极置入兔腰大肌,连接稳恒直流电源后构成的是一个RC电路,应用3V电压或者4V电压刺激都可以引起血管周围电势的变化.