Pore linings

Fig. 14. Coion partition coefficients SN for uni-univalent electrolyte, CF/w = 21.7 mmol/dm3, Kpn = w, calculated by the EVM (line A) or the ESM for slit-shaped pores (lines B-F) (i) Single pores of radius r = 6 (line B) or 40 (line F) nm. (ii) Assemblies of two pores of equal surface charge density of mean radius 6 nm and individual radii (in nm) 5.306,40 (line C) 5.454,80 (line D) 4.583,40 (line E) where 98 % (C), 99 / (D), or 96 % (E) of the total pore wall surface area is in narrow pores 121). Note that the power law of Eq. (46) is obeyed over a considerable range in cases C and E...

Niemeyer MI et al (2003) A conserved pore-lining glutamate as a voltage- and chloride-dependent gate in the C1C-2 chloride channel. J Physiol 553 873-879... 

The collapse of a polymer gel in response to a change in environment can be scaled down to the single chain level. A layer of polymer chains grafted to a surface forms a polymer brush, for which the collapse transition can be nicely observed using neutron reflectivity. A pore lined with a responsive polymer brush will form a selective valve for example if the grafted polymer is a weak polybase, in aqueous acidic conditions the brush will be charged and will expand to close the pore, while in basic conditions the brush will be neutral. This principle has been used to create a selective membrane, which shows greatly reduced permeability in acidic conditions. 

Zhelev, D.V. and Needham, D. (1993) Tension-stabilized pores in giant vesicles-determination of pore-size and pore line tension. Biochimica et Biophysica Acta, 1147 (1), 89-104. 

A in diameter. The only aqueous links between the inner vestibule and the cell interior are the narrow (<8-9 A wide) "windows" between the subunits lying directly under the membrane surface. The gate of the channel, made by the pore-lining segments, M2, is near the middle of the membrane (upper arrow), and the constriction zone (the narrowest part of the open channel) is at the cytoplasmic membrane surface (lower arrow). 

The acetylcholine receptor from skeletal muscle is a pen-tameric protein with a subunit composition of a2P78. The a, (3, y, and 8 subunits have considerable sequence homology on average, about 35-40 percent of the residues in any two subunits are similar. The complete receptor has fivefold symmetry, and the actual cation channel is a tapered central pore lined by homologous segments from each of the five subunits (Figure 7-45). 

FIGURE 7-46 Schematic models of the pore-lining M2 helices in the closed and opened states. In the closed state, the kink in the center of each M2 helix points inward, constricting the passageway, whose perimeter is indicated by the blue spheres. In the open state, the kinks rotate to one side, so that the helices are farther apart. The green spheres denote the hydroxyl groups of serine (S) and threonine (T) residues in the center of the M2 helices in the open state these are parallel to the channel axis and allow ions to flow. [Adapted from N. Unwin, 1995, Nature 373 31]... 

Our observations indicate that the recrystallization causes significant weakening of the test, although quantitative studies have not yet been conducted. Recrystallized tests crumble much more easily under moderate compressive stress and they are less able to withstand ultrasonic cleaning. Most obviously, the tests are no longer transparent, but opaque and chalky white (the so-called frosty appearance described by Sexton et al. 2006). It may be that organic membranes such as the POM and pore linings are destroyed in the recrystallization process, because we have only observed them in non-recrystallized material. 

Identification of presumed pore-lining segments is based on the primary structure of the channel protein and knowledge of the physiology of the molecule. Amphipathic a-helical segments greater than 20 residues in length —sufficient to span the width of the bilayer core—are identified by the use of empirical secondary structure predictors specific residues allow for appropriate ionic selectivity (6-8). 

A very important factor is the location and distribution of clay particles within the rock. The total clay content or clay type are not dependable indicators of the susceptibility of the rock to damage. The location of clays and the clay growth form tend to control the degree of damage susceptibility. A rock in which most of the clay is confined to shale streaks or mud rip up clasts is likely to be less susceptible to damage compared with the rock in which clay is present in the pore lining form. 

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