Membrane viscosity

H. Noguchi and G. Gompper, Dynamics of fluid vesicles in shear flow effect of membrane viscosity and thermal fluctuations, Phys. Rev. E 72, 011901 (2005). 

Haidekker MA, Ling T, Anglo M, Stevens HY, Frangos JA, Theodorakis EA (2001) New fluorescent probes for the measurement of cell membrane viscosity. Chem Biol 8(2) 123-131... 

Nadiv O, Shinitzky M, Manu H, Hecht D, Roberts CT Jr, LeRoith D, Zick Y (1994) Elevated protein tyrosine phosphatase activity and increased membrane viscosity are associated with impaired activation of the insulin receptor kinase in old rats. Biochem J 298(Pt 2) 443 150... 

Maczek C, Bock G, Jurgens G, Schonitzer D, Dietrich H, Wick G (1998) Environmental influence on age-related changes of human lymphocyte membrane viscosity using severe combined immunodeficiency mice as an in vivo model. Exp Gerontol 33(5) 485—498... 

The Vel data as a function of flow rate, Q, are shown for a 10 g/mol molecular weight polystyrene in Figure A. Both the Ubbelohde viscometric data and the membrane viscometer data are platted on the same graph for a 0.6 urn pore membrane at a low concentration of 100 ppm. The flow is Newtonian. The actual agreement of the capillary and membrane viscosities at low flow rates is always excellent when << Dj., and the concentration is extremely low. At small pore size, high concentrations, and high shear rates the flow can become non-Newtonian. The latter effects are only briefly discussed in this paper, but it is this effect that offers an oportunity to characterize the shape rather than the overall size. Even for a relatively large pore (0.6, Hi , membrane the shear rates vary from 100 s at E mi/Hr to 10 s at 200... 

Dunham, W.R., Klein, S.B., Rhodes, L.M., and Marcelo C.L., Oleic acid and linoleic acid are the major determinants of changes in keratinocyte plasma membrane viscosity, J. Invest. Dermatol., 107, 332, 1996. 

Phytosterols are structurally very similar to cholesterol and the major phytosterols (campesterol, sitosterol and stigmasterol) have the same kind of membrane viscosity modulating function in plants that cholesterol (C27 3-OH-C6 C6 G61 C5—C8) has in animals. Campesterol (24-methylcholesterol), sitosterol (24-ethylcholesterol) and stigmasterol (A22, 24-ethylcholesterol) are widespread phytosterols. The animal sterols lanosterol and cholesterol are present in particular plants. Phytosterol esters reduce cholesterol absorption and lower LDL-cholesterol. 

How rapidly diffusion occurs is characterized by the diffusion coefficient D, a parameter that provides a measure of the mean of the squared displacement x of a molecule per unit time f. For diffusion in two dimensions such as a membrane, this is given by = 4Ht. The Saffman-Delbrtlck model of Brownian motion in biologic membranes describes the relationship between membrane viscosity, solvent viscosity, the radius R and height of the diffusing species, and D for both lateral and rotational diffusion of proteins in membranes (3, 4). This model predicts for example that for lateral diffusion, D should be relatively insensitive to the radius of the diffusing species, scaling with log (1/R). 

Interestingly, the diffusional behavior of membrane proteins measured experimentally by FRAP, FCS, or single particle tracking in cells is more complex than predicted by this model. This technique is described best for the case of cell surface proteins, as assessed by FRAP. Such measurements indicate that diffusion is typically much slower than one would expect based on membrane viscosity. In cell membranes, typical values of D for transmembrane proteins are approximately 0.05 pm /s or less, which is much slower than observed in artificial membranes composed of purified lipids. In addition, a significant fraction of proteins is often immobile over the timescale of diffusion experiments (4, 5). Furthermore, diffusional mobilities vary among proteins, and sometimes they differ for the same protein expressed in different cell lines (4, 5). Deviations from pure diffusion are more readily apparent when the trajectories... 

Figure 47.3. Schematic illustrating twofold effects of Pluronic block copolymers witli intemiediate lipophilicity on Pgp and MRPs drag efflux system. Tliese effects include (a) decrease in membrane viscosity ( fluidization ) resulting in inliibition of Pgp and MRPs ATPase activity, and (b) ATP depletion in BMVEC. Extremely lipo-pliilic or hydi ophilic Plui onic block copolymers do not cross tire cel-lulai membranes and do not cause energy depletion in tire cells.

The free-volume parameters were estimated from viscosity and temperature data of pure components and the binary interaction parameter between the component and the polymer was determined using the group-contribution lattice-fluid equation of state (GCLF-EOS) (Alvarez, 2005, Alvarez et al, 2008). The innovative application of zero shear viscosity predicted data was proposed in this work for POMS free-volume parameters, as an alternative when experimental polymeric membrane viscosity data are scarce or inexistent. 

Kulkarni et al. [123] Recovery of Ni using D2EELPA Membrane viscosity, volume ratios of emulsion to... 

Kulkarni and (18C6). Extraction of Mo (VI) with Aliquat model. Residence time, membrane viscosity, extractant, strip... 

Several drawbacks are connected to the application of the surfactant concentration as the parameter controlling ELM stability. The first one originates from the increasing swelling of the ELM with increasing surfactant concentration, due to increasing affinity for water [76]. If the ELM is prepared from a Newtonian liquid, then the second major drawback is the decrease in the rates of mass transfer inside the ELM, due to an increase in the viscosity of the ELM [77]. If the LM is prepared from a non-Newtonian liquid, then the diffusion coefficient of the extracted solute is virtually independent ofthe membrane viscosity [78, 79], below the critical concentration [80]. This concentration can be calculated from Eq. (5), as derived by SkeUand and Meng [81]. 

Measurements of lateral diffusivity [131] as well as apparent membrane viscosity [133,134] have shown that membrane fluidity generally decreases with increasing MW (Fig. 7), as the most drastic decrease is detected when the chains are sufficiently long to entangle. 

Freezing and melting of lipid bilayers greatly alters the conductance mediated by a carrier, because it influences its mobility in the membrane. In contrast, the conductance induced by a channel former is not influenced158. Similarly, an increase of the membrane viscosity, by addition of cholesterol, reduces carrier-, but not channel- mediated conductance278,217. ... 

Oxe pera meter in addition to membrane viscosity that was important in determining lbe rate of copper uptake was the size of the interenl microdroplets. This can be contsulied by the way in which emulsions are made. Cahn et al.12 fonnd thet a 30% incrense in rate accrued from reducing the average size of (be microdroplet from 14 to 2 pm, This is illustrated hy the extraction curves in Fig. 19.3-3. Membrane... 

TABLE 19,3-1 Effects of Membrane Viscosity on Transport Rates... 

FIGURE 19,3-2 EUeci of membrane viscosity on copper extraction. From Cahn el al.12 with permission. 

Similar results were obtained by Volkel el al.M who also used LIX 64N as the carrier. Their extraction rates were somewhat slower than those reported by Cahn and coworkers, probably because of greater membrane viscosity. Volkel and coworkers also developed a fairly complicated mathematical model for membrane transport from which Ibey deierminnd mass transfer parameters. These ranged from I X 10 3 to I X I O 1 s 1. These are comperable to the values obtained for the extraction ofpbenoi (type 1 facilitated transfer in which no carrier is used) by the same group.16... 

Sigma, St. Louis, MO) in the solution. The results were not affected by the higher viscosity, which indicates that the mobility is determined by the membrane viscosity only and that even for the low-viscosity medium the rotational diffusion of the whole vesicles is too slow to affect the results. 

The recovery of metal ions from rinse solutions is important in electroplating. It has been shown in [291] that nickel ions can be recovered using a liquid surfactant membrane (LSM) obtained on the basis of di(2-ethylhexyl) phosphoric acid. The LMS permeation by nickel ions (external phase) is affected by the membrane viscosity which depends on the surfactant concentration. 

Figure 3 Schematic presenting multiple effects of Pluronic block copolymers displayed in MDR ceU. These effects include (a) decrease in membrane viscosity ( fluidization ) (b) ATP depletion (c,d) inhibition of drug efflux transport systems (e) reduction in GSH/GST detoxification activity and (f) drug release from acidic vesicles in the cell. Effects of Pluronic block copolymers on apoptosis (g) are not sufficiently studied at present. (From Ref. 94.)...

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