Electrical-to-Mechanical Coupling in Purple Membranes: Membrane as Electrostrictive Medium

Kietis, Povilas Bronius; Vengris, Mikas; Valkūnas, Leonas

doi:10.1016/s0006-3495(01)76135-8

Cited by 11 publications

(23 citation statements)

References 30 publications

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“…However, we do agree that salicylate makes the membrane more symmetric (Fig. 7), perhaps the salicylate effect measured with the AFM results form this observation; a more centric or less orientated material will have a different response to that observed from an acentric or asymmetric membrane [28]. We found that the additional linear component [Figs.…”

Section: Comparison With Experimental Measurements Obtained With Afmsupporting

confidence: 77%

“…For linear dielectrics both effects cause stresses and strains that are quadratic with the field, E and both are described for ceramics and polymeric materials [24][25][26][27]. Electrostrictive effects were demonstrated in dry purple membranes of Halobacterium salinarium at fields between 10 6 and 10 8 Vm −1 where the membranes thinned during application of an electric field [28]. When the films were orientated (not centric) the minimum of the parabolic function was at positive potentials, when the films were symmetric or weakly orientated the minimum of the parabolic function moved towards zero volts.…”

Section: B Maxwell Stress and Electrostrictive Effects Likely Originmentioning

confidence: 99%

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Voltage-dependent capacitance of human embryonic kidney cells

2006

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We determine membrane capacitance, C as a function of dc voltage for the human embryonic kidney (HEK) cell. C was calculated from the admittance, Y, obtained during a voltage ramp when the HEK cell was held in whole-cell patch-clamp configuration. Y was determined at frequencies of 390.625 and 781.25 Hz from the measured current, i obtained with a dual-sinusoidal stimulus. We find that the fractional increase in the capacitance, C is small (<1%) and grows with the square of the voltage, Ψ. C can be described by: [where C(0): Capacitance at 0 volts, ψ s : Difference in surface potential between cytoplasmic and extracellular leaflets and α: Proportionality constant]. We find that α and ψ s are 0.120 (±0.01) V −2 and −0.073 (±0.017) V in solutions that contain ion channel blockers and 0.108 (±0.29) V −2 and −0.023 (±0.009) V when 10 mM sodium salicylate was added to the extracellular solution. This suggests that salicylate does not affect the rate at which C grows with Ψ, but reduces the charge asymmetry of the membrane. We also observe an additional linear differential capacitance of about (−46 fFV −1 ) in about 60% of the cells, this additional component acts simultaneously with the quadratic component and was not observed when salicylate was added to the solution. We suggest that the voltage dependent capacitance originates from electromechanical coupling either by electrostriction and/or Maxwell stress effects and estimate that a small electromechanical force (≈1 pN) acts at physiological potentials. These results are relevant to understand the electromechanical coupling in outer hair cells (OHCs) of the mammalian cochlea, where an asymmetric bell-shaped C versus Ψ relationship is observed upon application of a similar field. Prestin, a membrane protein expressed in OHCs is required to observe this function. When we compare the total charge contributions from HEK cell membrane (7×10 4 electrons, 10 pF cell) with that determined for prestin transfected cells (up to 5×10 6 electrons) we conclude that the charge contributions from the collective motion of membrane proteins and lipids in the field is dwarfed relative to that when prestin is present. We suggest that the capacitance-voltage relationships should be similar to that observed for HEK cells for OHCs that do not express prestin in their membranes.

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Section: Comparison With Experimental Measurements Obtained With Afmsupporting

confidence: 77%

Section: B Maxwell Stress and Electrostrictive Effects Likely Originmentioning

confidence: 99%

Voltage-dependent capacitance of human embryonic kidney cells

2006

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“…Possibilities of orientation of the PM evidently confirm the existence of a permanent dipole moment at low frequencies and an induced dipole moment at high frequencies of the applied field [10][11][12][13][14]. This electric asymmetry seems to be responsible for the proton driving through the membrane [15].…”

Section: Introductionmentioning

confidence: 69%

“…Hence the dehydratation of the sample should have a crucial impact on the electric asymmetry of the PM. The internal DM of the PM in dried films causes their electrostrictive properties, which could be invoked for direct estimations of the value of the internal field [15]. As will be shown bellow, this value remains unchanged in the dried PM film even when pH is low, thus supporting the assumption of a different origin of this dipole moment than that detected in aqueous suspensions.…”

Section: Introductionmentioning

confidence: 71%

“…From the sign of the photoresponse signal it has been deduced that the cytoplasmic side is charged more negatively when pH is higher than 5 and vice versa when pH is less than 5 [22], while at pH 5 both sides are almost equally charged [22,23]. However, in accord with predictions [12] the inverse DM of the BR molecule under the normal external conditions directed from the cytoplasmic side to the extracellular side has been identified from studies of the dried PM films [15]. Hence the dehydratation of the sample should have a crucial impact on the electric asymmetry of the PM.…”

Section: Introductionmentioning

confidence: 85%

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Estimation of the permanent dipole moment of bacteriorhodopsin

Kietis¹

2010

Lithuanian J. Phys.

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The static electric dipole moment persisting in bacteriorhodopsin was defined from electro-acoustic measurements of the dried films of purple membranes and compared with the value estimated from quantum chemical calculations. The projection of this value normal to the membrane surface is experimentally estimated to be equal to 40 D and oriented from the cytoplasmic side to the extracellular side of the membrane. This value is almost independent of the environment pH. QM/MM calculations were also performed for the known structures of the ground and intermediate states of bacteriorhodopsin. According to calculations the dipole moment is mainly determined by the cytoplasmic and extracellular coils, while the contribution from the transmembrane helices is smaller and of the opposite direction, and this value corresponding to the active centre is small. The calculated values of the dipole moment of bacteriorhodopsin in the intermediate states K, L, and M provide understanding about the origin of the driving force for the proton pumping. Employing the values of the dipole moments corresponding to the ground and intermediate states of bacteriorhodopsin, defined by means of QM/MM calculations, the experimentally determined photoelectric response of the dried films is explained.

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External electric control of the proton pumping in bacteriorhodopsin

Kietis¹,

Saudargas²,

Váró

et al. 2006

Eur Biophys J

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Comparative analysis of the photoelectric response of dried films of purple membranes (PM) depending on their degree of orientation is presented. Time dependence of the photo-induced protein electric response signal (PERS) of oriented and non-oriented films to a single laser pulse in the presence of the external electric field (EEF) was experimentally determined. The signal does not appear in the non-oriented films when the EEF is absent, whereas the PERS of the oriented PM films demonstrates the variable polarity on the microsecond time scale. In the presence of the EEF the PERS of the non-oriented film rises exponentially preserving the same polarization. The polarization of the PERS changes by changing the polarity of the EEF with no influence on the time constant of the PERS kinetics. The EEF effect on the PERS of the oriented films is more complicated. By subtracting the PERS when EEF not equal 0 from the PERS when EEF = 0 the resulting signal is comparable to that of the non-oriented films. Generalizing the experimental data we conclude that the EEF influence is of the same origin for the films of any orientation. To explain the experimental results the two-state model is suggested. It assumes that the EEF directionally changes the pK(a) values of the Schiff base (SB) and of the proton acceptor aspartic acid D85 in bacteriorhodopsin. Because of that the SB-->D85 proton transfer might be blocked and consequently the L-->M intermediate transition should vanish. Thus, on the characteristic time scale tau( L --> M ) approximately 30 micros; both intermediates, the M intermediate, appearing under normal conditions, and the L intermediate as persisting under the blocked conditions when D85 is protonated, should coexist in the film. The total PERS is a result of the potentials corresponding to the electrogenic products of intermediates L and M that are of the opposite polarity. It is concluded that the ratio of bacteriorhodopsin concentrations corresponding to the L and M intermediates is driven by the EEF and, consequently, it should define the PERS of the non-oriented films. According to this model the orientation degree of the film could be evaluated by describing the PERS.

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Electrical-to-Mechanical Coupling in Purple Membranes: Membrane as Electrostrictive Medium

Cited by 11 publications

References 30 publications

Voltage-dependent capacitance of human embryonic kidney cells

Voltage-dependent capacitance of human embryonic kidney cells

Estimation of the permanent dipole moment of bacteriorhodopsin

External electric control of the proton pumping in bacteriorhodopsin

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