Lipids cation distributions

Once formed phosphonium salts could have a significant effect on cellular processes, particularly on mitochondrial function. Ph3PMe has been used as a probe to measure membrane potentials, for instance in thyroid cells lymphocytes Escherichia and human granulocytes The lipid-soluble cation distributes itself across the membrane in accordance with the membrane potential Monovalent lipophilic cations which have significant membrane permeability are concentrated in mitochondria. For instance the laser dye Rhodamine 123 has been used as a specific probe for the localisation of mitochondria in living cells It has also been shown to have in vivo antitumour activity ... 

In contrast, solid lipid microparticles consisting of a tripalmitin matrix and cationic lipids prepared using the micromixer-based solvent extraction process as described by Emi et al. [50] were of monomodal size, showing a narrow size distribution in the submicrometer range (Table 8.1). 

The first of these environmentally-important parameters can be expressed as a partition coefficient. In aqueous solution many, but not all pesticide compounds exhibit strong affinity for soil organic matter or concentrate in the lipid phase of soil organisms. Some, notably the cationic group, also exhibit marked affinity for clay or other mineral surfaces. An overall partition (or distribution) coefficient (kD) can be defined ... 

We have actually measured the electrical potential differences in intact purple membrane bacteria, using the distribution of a lipid-soluble cation as an indicator, and found values of up to 100 mV[E. Bakker,H. Rottenberg, and S. R. Caplan, Biochim. Biophys. Acta, 440, 557 (1976)]. These values obviously correspond to enormous potential gradients across the membrane. 

Zelphati, O. and Szoka, F. (1996a) Intracellular distribution and mechanism of delivery of oligonucleotides mediated by cationic lipids. Pharm. Res., 13, 1367-1372. 

By introducing a crown ether unit at the C-terminal region of hydrophobic helical peptides, Otoda et al.19 were able to demonstrate increased stabilization of the peptide aggregate in the membrane by the formation of sandwich-type complexes with large cations. Ion channel activity was also increased due to the ability of the crown peptide to bind ions to the terminal portion of the hydrophobic helix bundle at the water-lipid interface. Ueda et al.20 considered the problem of insolubility of hydrophobic peptides which restricts the distribution of peptides in water to a phospholipid bilayer membrane. In consequence they constructed a hydrophobic helix bundle shielded by hydrophilic peptides that acts rather like an umbrella. 

Figure 27. Dynamical scaling of DNA confined to the surface of a supported lipid membrane, (a) Time sequence (At = 30 s) of a DNA molecule diffusing on a cationic lipid membrane. The image on the right depicts an overlay of 16 images time average yields a smeared fluorescence distribution, (b) Scaling behavior of the self-diffusion coefficient of the center of mass D with the number of base pairs, (c) Scaling behavior of the rotational relaxation time r, with the number of base pairs.140...

Shape, size distribution and transfection capability of these complexes depend on composition and charge ratio of nucleic acid to that of the cationic lipid/polymer. 

Osaka, G., Carey, K., Cuthbertson, A., Godowski, P Patapoff, T., Ryan, A., Gadek, T., and Mordenti, J. (1996) Pharmacokinetics, tissue distribution, and expression efficiency of plasmid [33P]DNA following intravenous administration of DNA/cationic lipid complexes in mice—use of a novel radionuclide approach. J. Pharm. Sci. 85(6), 612-618. 

Parker, S. E., Ducharme, D., Norman, J., and Wheeler, C. J. (1997) Tissue distribution of the cytofectin component of a plasmid DNA/cationic lipid complex following intravenous administration in mice. Hum. Gene Ther. 8(4), 393 401. 

The absorption of tetracyclines from the G1 tract is non-uniform. Up to 30% of chlortetracycline is absorbed. The absorption for tetracycline, oxytetracycline, and demeclo-cycline ranges between 60 and 80%, whereas as much as 90 to 100% of doxycycline and minocycline is absorbed. The absorption of tetracyclines is impaired by divalent cations (calcium, magnesium, and ferrous iron), by aluminum, and by extremely alkaline pHs. Tetracyclines are distributed widely throughout the body fluid, cross the placental barrier, and can accumulate in growing bones. The concentrations of chlortetracycline in spinal fluid are only one fourth of those in plasma. Minocycline, a more lipid-soluble tetracycline, reaches a high concentration in tears and saliva and can eradicate the meningococcal carrier state. The tetracyclines are metabolized in the liver and excreted mainly by the bile and urine. The concentrations of tetracyclines in the bile are ten times higher than those in serum. 

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