Lipid domains viscosity

Theoretical models of the film viscosity lead to values about 10 times smaller than those often observed [113, 114]. It may be that the experimental phenomenology is not that supposed in derivations such as those of Eqs. rV-20 and IV-22. Alternatively, it may be that virtually all of the measured surface viscosity is developed in the substrate through its interactions with the film (note Fig. IV-3). Recent hydrodynamic calculations of shape transitions in lipid domains by Stone and McConnell indicate that the transition rate depends only on the subphase viscosity [115]. Brownian motion of lipid monolayer domains also follow a fluid mechanical model wherein the mobility is independent of film viscosity but depends on the viscosity of the subphase [116]. This contrasts with the supposition that there is little coupling between the monolayer and the subphase [117] complete explanation of the film viscosity remains unresolved. 

As shown in figure 7.22(A), increases in membrane static order caused by supplementing the growth medium of Chinese hamster ovary cells with cholesterol led to regular decreases in the specific activity of the Na+-K+-ATPase (Sinensky et al., 1979). Presumably, the increased viscosity of the domain of lipids adjacent to the enzyme hindered the conformational changes required for ion transport, leading to reductions in enzymatic activity. 

For EAC cells membranes, the compound (almost over the entire concentration range) decreases significantly the microviscosity of surface lipids and near-protein domains of the lipid bilayer only at the HA concentrations 10"16 and 10"4 M, the viscosity increases. In particular, the compound dose 10"5 M affects the Ca2+ signal system of EAC cells. At lower ichfan concentrations (10 8 M), the membrane microviscosity decreases and the compound produces no effect on the cell volume. Evidently, over this concentration range, the compound produces no effect on the membrane and Ca2+ signal system. 

The effect of an electric field on the movement of domains in lipid monolayers was studied by Heckl et al. (1988) (cf Fig. 3D.1). The mobility of domains in an inhomogeneous electric field depends on the surface viscosity and leads to special cluster formation. 

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