Membrane dipole potential

D. Water Orientational Polarization and the Membrane Dipole Potential... 

Vitha MF, Clarke RJ (2007) Comparison of excitation and emission ratiometric fluorescence methods for quantifying the membrane dipole potential. Biochim Biophys Acta-Biomembr 1768(1) 107—114... 

Clarke RJ, Kane DJ (1997) Optical detection of membrane dipole potential avoidance of fluidity and dye-induced effects. Biochim Biophys Acta Biomembr 1323(2) 223-239... 

Keywords Dual-wavelength ratiometry Electrochromism Ion-transporting membrane proteins Membrane dipole potential Phototoxicity... 

Flewelling, R. F. and Hubbell, W. L. (1986). The membrane dipole potential in a total membrane potential model applications to hydrophobic ion interactions with membranes, Biophys. J., 49, 541-552. 

The membrane dipole potential role in modulating microdomain-located membrane proteins... 

Many membrane components such as phospholipid include moieties such as the C + = and 0 -P + exhibit polarisation. The membrane dipole potential ( )d has its origins in the dipole moments of polar groups from the lipidic components of the bilayer, it seems likely that the water molecules at the molecular surface of membrane also make a contribution (1). The organisation of the membrane components that contribute to this potential have been verified from neutron diffraction studies and NMR spectroscopy (23) and quite recently using cryo-EM techniques has also added quantitative estimations of the potential (24). These dipolar groups seem to be oriented in a way such that the potential located towards the hydrophobic interior of the membrane is positive with respect to the pole located towards... 

Figure 3 Fluorescent sensors of Surface and Dipole potential in membranes. Fig. 3a (LHS) indicates the position in the a single bilayer leaflet of fluorescent indicators of the membrane dipole potential (upper chemical structure) and the surface potential (lower chemical structure). The RHS profile indicates how the profile of surface potential varies with distance from the membrane surface. Fig. 3b indicates the use of FPE as a surface potential indicator that responds to the addition of a charged peptide (P25) as it interacts with simple membranes (see 25 for more details).

This expression, however, only deals with a single molecular dipole and as many such dipoles would be required to describe the overall membrane dipole potential but as a mean-field expression, this term is practical and culmulatively offers the approximation of the estimated dipolar organisation shown in Fig. 4. A further complication, however, involves the solvent environment and this too is also often dealt with as a mean field or in a continuum manner. But the relative permittivity (or dielectric constant) (sr) cannot be considered to possess the same value throughout the multiphase system represented by a membrane in an aqueous medium. The permittivity profile has been measured to vary from about 78.5 in the bulk aqueous... 

The excitation spectrum of di-8-ANEPPS is altered when it lines up (symmetrically or asymmetrically) with the membrane dipoles causing electronic redistributions within the probe molecule (see e.g. Fig. 5a). This promotes red or blue shifts in the excitation spectrum depending on the magnitude and direction of the dipole moment of the ambient environment that the probe finds itself in as shown in Fig. 5b. Preparation of membranes with sterols etc (ie that possess quite different dipole-moments to PC) promote changes in the membrane dipole potential, and significant variations of the intensity and position of the excitation maximum are observed. The excitation spectrum of di-8-ANEPPS in phosphatidylcholine (PC) membranes for example is significantly altered when 15mol% of either 6-ketocholestanol (KC) or phloretin are added to such membranes. In the case of phloretin the difference spectmm has a minimum at 450 nm and a maximum at 520 nm (Fig. 5b). In the case of KC, however, the difference spectrum has a maximum at 450 nm and a minimum at 520 nm, which is the opposite effect to that of phloretin. 

Figure 5 Spectroscopic tools for identifying the membrane dipole potential Fig. 5a indicates the excitation spectrum of different membranes labeled with di-8-anepps with the emission collected at 580nm. Spectra are shown for membranes made up of 100% phosphatidylcholine (-), membranes made up of...

Asawakarn T, Cladera J, O Shea P. Effects of the membrane dipole potential on the interaction of Saquinavir with phospholipid membranes and plasma membrane receptors of Caco2 cells. J. Biol. Chem. 2001 276 38457-38463. 

Langner M, Hui SW. Merocyanine interaction with phosphatidylcholine bilayers. Biochim. Biophys. Acta. 1993 1149 175-179. Ross E, Bedlack RS, Loew EM. Dual-wavelength ratiometric fluorescence measurement of the membrane dipole potential. Biophys. J. 1994 67 208-216. 

Gawrisch, K., Ruston, D., Zimmerberg, J., Parsegian, V.A., Rand, R.R, and Fuller, N. Membrane dipole potentials, hydration forces, and the ordering of water at membrane surfaces, Biophys.., 61, 1213, 1992. 

They found other peculiarities when studying the transport of L-tryptophan in human freshly sampled red cells uptake could be resolved into linear and saturable components but upon infection or storage of red cells the linear component was substantially increased whereas the Kt and maximum velocity (Vmax) remained constant. (They also contended that the presence of parasitized red cells altered the permselectivity of uninfected red cells.) Further, the changes in the permselectivity of the P. falciparum-infected red cells was unaffected by p-chloromercuribenzoate (PCMB) and cytochalasin B, inhibitors for glucose transport, as well as DIDS and DNDS for anion transport, but was inhibited by phloretin, a modifier of the membrane dipole potential shown to block a variety of mediated and non-mediated transport mechanisms. Phloretin also inhibited the in vitro growth of P. falciparum. This work is reviewed in Ginsburg and Kirk, 1998. 

Rokitskaya, T. I., Kotova, E. A., and Antonenko, Y. N. [2002]. Membrane dipole potential modulates proton conductance through gramicidin channel ... 

The simulation of lipid bilayers provides a method for probing microscopic details of the lipid system, and relates those details to the macroscopic behavior observed experimentally.The molecular dynamics approach is the most popular choice for membrane simulation, because it provides information about the spatial and temporal evolution of both single species phospholipid membranes, and multi-lipid systems. For example, molecular dynamics allowed for the characterization of phospholipid bilayers in terms of their interaction with water, and revealed that the orientation of the water molecules compensated for the fluctuations in the lipid head group, resulting in an almost constant membrane dipole potential. 

Figure 7.3 Origin of membrane dipole potential. Key, A-phosphatidyl choline and dipole structure, B—location of cholesterol, C—ion adsorption, D—long-range dipole interaction involving macromolecule, E—dipole contribution of membrane embedded species. See Figure 7.2 for description of modes of ion transport (centre of diagram). Right of figure depicts dipole potential. (Reprinted by kind permission of Elsevier Science Publishers, B.V., Amsterdam).

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