Alkali and Alkaline Earth Metal Ions in Biochemical Systems
Pabitra Krishna Bhattacharya, Prakash B. Samnani in Metal Ions in Biochemistry, 2020
The intra- and extracellular concentrations of the metal ions are important in various processes like signalling. Working of Na/K pump has been described along with experimental evidence. Adenosine triphosphates supply energy for movement of the ions across membranes. However, after few milliseconds of the transmembrane potential change, the original intra- and extracellular concentration levels of the alkali metal ions and transmembrane potential are restored, by the back diffusion of K inside the cell and of Na outside the cell. Hence, the membrane should inhibit the passive transport of the charged alkali metal ions across it. The ionophores bind with the metal ion through the polar oxygen site and show selectivity in binding with the alkali metal ions. The ionophores present in biological membrane have much greater degree of selectivity, but in alkali metal transport, they have to discriminate only between Na and K, as other alkali metal ions, such as Li, Rb and Cs, are in negligible amounts.
Membrane Transport of Small Molecules and the Electrical Properties of Membranes
Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter in Molecular Biology of the Cell, 2017
Because of its hydrophobic interior, the lipid bilayer of cell membranes restricts the passage of most polar molecules. This barrier function allows the cell to maintain concentrations of solutes in its cytosol that differ from those in the extracellular fluid and in each of the intracellular membrane-enclosed compartments. Like synthetic lipid bilayers, cell membranes allow small nonpolar molecules to permeate by diffusion. Cell membranes, however, also have to allow the passage of various polar molecules, such as ions, sugars, amino acids, nucleotides, water, and many cell metabolites that cross synthetic lipid bilayers only very slowly. All channels and many transporters allow solutes to cross the membrane only passively, a process called passive transport. Lipid bilayers are virtually impermeable to most polar molecules. The process by which a transporter transfers a solute molecule across the lipid bilayer resembles an enzyme–substrate reaction, and in many ways transporters behave like enzymes.
Interspecific Interactions
A.J. Nappi in Parasites of Medical Importance, 2002
Commensalism is a type of symbiotic association which is beneficial to one species and at least without any detectable adverse effect on the other species. The basis for such a relation may be food, substrate, space, or shelter. The commensal is usually the smaller o f the two species and may be attached to the exterior of the host (ectocommensal), or live within the body of the host (endocommensal). Examples include certain tropical commensal fishes, which are protected from predation by living among the tentacles o f certain sea anemones, and the pilot and remora fishes, which associate with sharks, sea turtles, or other species of fish usually feeding on “leftovers”. If the association is only a passive transport of the commensal by the host, the relationship is referred to as phoresy. Phoresy is essentially an accidental association with no metabolic dependency or interaction between the two individuals.
The absorption characteristics of bifendate solid dispersion in rat intestinal tissue
Published in Drug Development and Industrial Pharmacy, 2010
Juan Cheng, Zheng Hong Wu, Qineng Neng Ping, Bogang Wang, Junjun Lu
Aim: Research on bifendate intestinal absorption. Method: The single passed intestinal backflow method was used. Bifendate with different concentrations, bifendate with and without 2,4-dinitrophenol, verapamil, and probenecid, and solid state of bifendate in different systems were studied. Result: Change of concentration and the presence of energy inhibitor, P-glycoprotein inhibitor and multidrug-resistant protein inhibitor did not affect the Ka of bifendate intestinal absorption; there were obvious differences among intestinal absorption of native drug, solid dispersion, and physical mixtures. Conclusion: The result indicated that the intestinal absorption mechanism of bifendate is passive transport. Solid state of bifendate in different systems could affect the intestinal absorption.
Nuclear gene delivery: the Trojan horse approach
Published in Expert Opinion on Drug Delivery, 2006
The nuclear envelope represents a formidable barrier to the transfer of plasmids to the cell nucleus, particularly in nondividing cells. The probability of intact plasmids arriving in the nucleus by a passive process is extremely low. There is substantial evidence in the literature that describes the transport of macromolecules, including plasmids, to the nucleus as a very inefficient process, and so far attempts to affect the active transport through the nuclear pores have achieved limited success. Several approaches have been attempted to improve nuclear transport of plasmids, including the condensation of plasmids to unimolecular complexes of minimal hydrodynamic diameter to favour passive transport through the nuclear pore complex, and the incorporation of nuclear localisation signals in the plasmid or in the delivery system to enhance the active transport of plasmids through the nuclear pores.
A simple method of microneedle array fabrication for transdermal drug delivery
Published in Drug Development and Industrial Pharmacy, 2013
Jaspreet Singh Kochhar, Wei Jiang Goh, Sui Yung Chan, Lifeng Kang
The outermost layer of skin, stratum corneum, being lipophilic limits the passive transport of hydrophilic and large molecular weight drugs. Microfabrication technology has been adapted to fabricate micron scale needles, which are minimally invasive, yet able to deliver the drugs across this barrier layer. In this study, we fabricated microneedles from a biocompatible polymer, namely, poly (ethylene glycol) diacrylate. A simple lithographical approach was developed for microneedle array fabrication. Several factors including polymerization time, ultraviolet light intensity and distance from light source were studied for their effects on microneedle formation. The microneedle length and tip diameter can be controlled by varying these factors. The microneedles were shown to be able to penetrate cadaver pig skin. Model drug rhodamine B was encapsulated in the range of 50 µg to 450 µg per microneedle array. The fabricated microneedles containing rhodamine B increased the permeability by four times than the control. Altogether, we demonstrated that the microneedle arrays can be fabricated through a simple single-step process and needles were mechanically strong to penetrate skin, increasing the permeability of encapsulated drug through skin.
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