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  • 1
    Electronic Resource
    Electronic Resource
    Apparent activation volumes of hydrophobic ions and carriers in planar lipid bilayers (1985)
    Springer
    The journal of membrane biology 84 (1985), S. 221-227 
    Details
    ISSN: 1432-1424
    Keywords: activation volume ; planar bilayers ; hydrophobic ions ; ionophores ; pressure ; electrostriction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A gas-free high-pressure cell has been developed to measure planar bilayer conductances induced by hydrophobic ions and ionophores as a function of hydrostatic pressure. Plots of log conductance versus pressure for valinomycin and nonactin-mediated potassium transport in egg phosphatidyl cholinedecane membranes are essentially linear over a pressure range of 1 to 818 atm. Calculated activation volumes give similar results for both nonactin and valinomycin yielding values of +48 and +42 cc/mole, respectively. The valinomycin activation volume agrees reasonably well with the results obtained by Johnson and Miller (Biochim. Biophys. Acta 375:286–291, 1975) for K+-valinomycin transport in liposomes. In contrast to the activation volumes for nonactin and valinomycin, relaxation measurements of tetraphenyl boron (TPB) and dipicrylamine (DPA) give very small values of 〈5 cc/mole for the translocation rate constant,k i . Similarly, steady-state conductance measurements on tetraphenyl arsonium (TPA) and carbonylcyanidem-chlorophenylhydrazone (CCCP), give small values of 6 and 7 cc/mole, respectively. These low figures do not support transport theories based on the formation of bilayer holes or kinks (H. Träuble,J. Membrane Biol. 4:193–208, 1971). The low values for TPB and TPA are especially interesting because their cross-sectional areas are not much different than those of valinomycin and nonactin. Pressure-induced changes in membrane dielectric constant and thickness which lower the bilayer electrostatic barrier could explain the low values for the hydrophobic ions. Additionally, larger activation volumes might be expected for carriers such as nonactin and valinomycin that undergo significant rearrangement and change in hydration during surface complexation of cations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871385
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  • 2
    Electronic Resource
    Electronic Resource
    ESR measurement of time-dependent and equilibrium volumes in red cells (1990)
    Springer
    The journal of membrane biology 115 (1990), S. 31-40 
    Details
    ISSN: 1432-1424
    Keywords: erythrocyte ; ESR ; water ; permeability ; microviscosity ; transport ; osmosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Red cell water volumes were measured using ESR methods during transient osmotic perturbation, and under equilibrium conditions. Cell water contents were determined using the spin label Tempone (2,2,6,6-tetramethyl piperidine-N-oxyl) and the membrane impermeable quencher potassium chromium oxalate. With appropriate corrections for intracellular viscosity and changes in cavity sensitivity, equilibrium cell water measured both by electron spin resonance (ESR) and wet minus dry weight methods gave excellent agreement in solutions from 243–907 mOsm. Intracellular viscosities determined from the Tempone correlation times in the same cells gave values ranging from 9–47 centipoise at 21°C. Osmotically induced transient volume changes were measured using Tempone and an ESR stopped-flow configuration. The Tempone response time was estimated at 17 msec compared to 250–350 msec for normal water relaxations. Nonlinear least square solutions to the Kedem-Katchalsky equations including a correction for the finite Tempone permeability gave 0.029 and 0.030 cm/sec for the osmotic permeability of RBCs in swell and shrink experiments, respectively. In stopped-flow experiments accurate water flux data are obtained very soon after challenging cells and do not require baseline subtractions. These results represent significant improvements over conventional light scattering techniques which necessitate corrections for long lasting optical artifacts (200–300 msec), and baseline drifts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869103
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  • 3
    Electronic Resource
    Electronic Resource
    Estimate of the number of urea transport sites in erythrocyte ghosts using a hydrophobic mercurial (1993)
    Springer
    The journal of membrane biology 133 (1993), S. 85-97 
    Details
    ISSN: 1432-1424
    Keywords: urea transport ; erythrocytes ; mercurials ; spin labels ; electron spin resonance ; hydrophobicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In this paper a variety of mercurials, including a pCMB-nitroxide analogue, were used to study urea transport in human red cell ghosts. It was determined that the rate of inhibition for pCMBS, pCMB, pCMB-nitroxide, and chlormerodrin extended over four orders of magnitude consistent with their measured oil/water partition coefficients. From these results, we concluded that a significant hydrophobic barrier limits access to the urea inhibition site, suggesting that the urea site is buried in the bilayer or in a hydrophobic region of the transporter. In contrast, the rate of water inhibition by the mercurials ranged by only a factor of four and did not correlate with their hydrophobicities. Thus, the water inhibition site may be more directly accessible via the aqueous phase. Under conditions that leave water transport unaffected, we determined that ≤32,000 labeled sites per cell corresponded to complete inhibition of urea transport. This rules out major transmembrane proteins such as band 3, the glucose carrier, and CHIP28 as candidates for the urea transporter. In contrast, this result is consistent with the Kidd (Jk) antigen being the urea transporter with an estimated 14,000 copies per cell. From the experimental number of urea sites, a turnover number between 2–6×106 sec−1 at 22°C is calculated suggesting a channel mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231880
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  • 4
    Electronic Resource
    Electronic Resource
    Modification of the erythrocyte membrane dielectric constant by alcohols (1988)
    Springer
    The journal of membrane biology 104 (1988), S. 57-68 
    Details
    ISSN: 1432-1424
    Keywords: red blood cell ; dielectric constant ; permeability ; hydrophobic ions ; alcohols ; bilayer ; Born energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Aliphatic alcohols are found to stimulate the transmembrane fluxes of a hydrophobic cation (tetraphenylarsonium, TPA) and anion (AN-12) 5–20 times in red blood cells. The results are analyzed using the Born-Parsegian equation (Parsegian, A., 1969,Nature (London) 221:844–846), together with the Clausius-Mossotti equation to calculate membrane dielectric energy barriers. Using established literature values of membrane thickness, native membrane dielectric constant, TPA ionic radius, and alcohol properties (partition coefficient, molar volume, dielectric constant), the TPA permeability data is predicted remarkably well by theory. If the radius of AN-12 is taken as 1.9 Å, its permeability in the presence of butanol is also described by our analysis. Further, the theory quantitatively accounts for the data of Gutknecht and Tosteson (Gutknecht, J., Tosteson, D.C., 1970,J. Gen. Physiol. 55:359–374) covering alcohol-induced conductivity changes of 3 orders of magnitude in artificial bilayers. Other explanations including perturbations of membrane fluidity, surface charge, membrane thickness, and dipole potential are discussed. However, the large magnitude of the stimulation, the more pronounced effect on smaller ions, and the acceleration of both anions and cations suggest membrane dielectric constant change as the primary basis of alcohol effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871902
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  • 5
    Electronic Resource
    Electronic Resource
    Detection of functional groups and antibodies on microfabricated surfaces by confocal microscopy (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 60 (1998), S. 137-146 
    Details
    ISSN: 0006-3592
    Keywords: fluorescence confocal microscopy ; microfabrication ; aminosilane ; mercaptosilane ; antibody immobilization ; heterobifunctional crosslinker ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fluorescence confocal microscopy was used to characterize micron-sized microfabricated silicon particles and planar oxide surfaces after silanization and immobilization of IgG antibody. Surfaces treated with amino- and mercaptosilanes were tested for the presence of amine and sulfhydryl groups by labeling with specific fluorescein probes. In addition, human antibody (IgG) was immobilized to the thiol-coated microparticles using the heterobifunctional crosslinker succinimidyl 4-(N-maleimidolmethyl)-cyclohexane-1-carboxylate. Estimates of the surface density of IgG were consistent with 8.3% of a monolayer of covalently-bound antibody. Confocal images confirmed uniform layers of both silanes and antibodies on the microparticles. The sensitivity limit for the confocal measurements was determined to be as low as 1.5 × 10-5 fluors per nm2. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 60: 137-146, 1998.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction of charged lipid vesicles with planar bilayer lipid membranes: Detection by antibiotic membrane probes (1976)
    New York, N.Y. : Wiley-Blackwell
    Journal of Supramolecular Structure 5 (1976), S. 409-416 
    Details
    ISSN: 0091-7419
    Keywords: antibiotics ; bilayer lipid membranes ; surface charfe ; phospholipid vesicles ; fusion ; Life Sciences ; Molecular Cell Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: A technique has been developed for monitoring the interaction of charged phospholipid vesicles with planar bilayer lipid membranes (BLM) by use of the antibiotics Valinomycin, Nonactin, and Monazomycin as surface-charge probes. Anionic phosphatidylserine vesicles, when added to one aqueous compartment of a BLM, are shown to impart negative surface charge to zwitterionic phosphatidylocholine and phosphatidylethanolamine bilayers. The surface charge is distributed asymmertically, mainly on the vesicular side of the BLM, and is not removed by exchange of the vesicular aqueous solution. Possible mechanisms for the vesicle-BLM interactions are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jss.400050313
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