Membrane junctions

The interest in vesicles as models for cell biomembranes has led to much work on the interactions within and between lipid layers. The primary contributions to vesicle stability and curvature include those familiar to us already, the electrostatic interactions between charged head groups (Chapter V) and the van der Waals interaction between layers (Chapter VI). An additional force due to thermal fluctuations in membranes produces a steric repulsion between membranes known as the Helfrich or undulation interaction. This force has been quantified by Sackmann and co-workers using reflection interference contrast microscopy to monitor vesicles weakly adhering to a solid substrate [78]. Membrane fluctuation forces may influence the interactions between proteins embedded in them [79]. Finally, in balance with these forces, bending elasticity helps determine shape transitions [80], interactions between inclusions [81], aggregation of membrane junctions [82], and unbinding of pinched membranes [83]. Specific interactions between membrane embedded receptors add an additional complication to biomembrane behavior. These have been stud-... 

Aqueous Apical Tight Basolateral Aqueous Bulk Boundary Layer Membrane Junction Membrane Boundary Layer Bulk... 

A glass electrode which takes advantage of rapid and reproducible ion exchange across a glass membrane located as a thin-walled bulb at the tip of the electrode. This membrane has the following liquid-membrane junction ... 

A regular maintenance schedule and proper storage of the pH electrode ensures proper performance, helps extend the life of the electrode, and avoids the cost of replacements. On a weekly basis the electrodes should be inspected for scratches, cracks, deposits, and membrane-junction deposits. The reference chamber of refillable electrodes should be drained, flushed with fresh filling solution, and refilled. (Note The chamber should only be filled to about 75 to 80% of capacity, to allow expansion during temperature change.) This maintenance procedure will keep the electrode ready to use and improve the lifetime of the electrode. A standard glass electrode in normal use can last for up to two years. 

The simplest extension to real device operation in a stationary state consists in introducing losses via a series resistance Rs, which represents contact resistances, Ohmic losses in the front contact grid and in the rear contact, and a parallel resistance Rp, which includes any current bypassing the membranes (junction), and even shunt currents through short-cuts. 

This 3.6-A stmcture of Aquaporin-4 (Fig. 3c) was determined by electron crystallography of double-layered 2-D crystals (56). Features in the stmcture show that Aquaporin-4 can form membrane junctions, and they suggest for the first time its role in cell adhesion. This stmcture is of additional interest in that it is the first stmcture of a multispanning mammalian membrane protein obtained by purely recombinant methods. 

Kunst B and Lovrecek B. Electrochemical properties of ion-exchange membrane junctions. Croat. Chem. Acta 1962 34 219-225. 

Fig. 9 Field-enhanced water dissociation increases ionic currents in (a) a reverse-biased 20 nm thick bipolar-junction nanolluidic channel containing positive and negative surface charges (IVnil > 0.6 V), and (b) a UV-polymerized bipolar membrane V < —10 V). (c) Hydroxide ions and protons are produced at the bipolar membrane Junction and transport to opposite sides of the membrane. The pH change of the solution in the microchannels can be observed with a mixture of universal pH indicator. Left half of the bipolar membrane is positively charged whereas the right half is negatively charged...

B. Lovrecek and B. Kunst, Electrochemical properties of the ion-exchange membrane junction. I. Croa. Chem. Acta, 1962, 34, 137-150 M. Seno and T. Yamabe, On the electrolytic rectification effect in ion exchange membranes, Bull. Chem. Soc. Jpn.,... 

B. Lovrecek and B. Kunst, Rectifying mechanism of pressed sandwich type membrane junctions, Electrochim. Acta, 1972, 12, 687-692. 

H. Holdik, A. Alcaraz, P. Ramirez and S. Mafe, Electric field enhanced water dissociation at the bipolar membrane junction from ac impedance spectra measurement,./ Electroanal. Chem., 1998, 442, 13-18. 

The double vertical stroke after indicates a membrane junction or salt bridge. The double stroke shows the termination of one half-cell and the beginning of the second. This cell could also be written to show the salts used, as shown ... 

Liu V, Song YA, Han JY (2010) Capillary-valve-based fabrication of ion-selective membrane junction for electrokinetic sample preconcentration in PDMS chip. Lab Chip 10(11) 1485-1490... 

It was shown that conducting polymer as the phase characterized with mixed conductivity exhibits metallic behavior in the open-circuit (identical to noble metals or carbon) in contact with the element (membrane, junction, solution) containing the redox pair, according to the Nemst equation ... 

Sandifer, J.R. and R.P. Buck. 1975. An algorithm for simulation of transient and alternating current electrical properties of conducting membranes, junctions, and one-dimensional, finite galvanic cells. J. Phys. Chem. 79 384-392. 

Azamia, R., and Loewenstein, W. R., 1971, Intercellular communication and tissue growth. V. A cancer cell strain that fails to make permeable membrane junctions with normal cells, /. Membrane Biol. 6 368. 

Loewenstein, W. R., 1972, Cellular communication through membrane junctions. Arch Intern. Med. 129 299. 

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