Cation efflux system

Nies DH, Nies A, Chu L, Silver S (1989) Expression and nucleotide sequence of a plasmid-determined divalent cation efflux system from Alcaligenes eutrophus. Proc Natl Acad Sci USA 86 7351-7355... 

Saitoh, H., Aungst, B. J., Possible involvement of multiple P-glyco-protein-mediated efflux systems in the transport of verapamil and other organic cations across rat intestine, Pharm. Res. 1995, 12, 1304-1310. 

One of the most important efflux transporters identified at the BBB is the Pgp efflux system. This system is discussed in more detail because its presence has been demonstrated at the luminal site of the BBB endothelium (42) and it has been extensively studied in past decades. The Pgp efflux system is responsible for the occurrence of multidrug resistance (MDR), and today, Pgp is considered as an amphipatic cationic efflux pump. 

Nies, D. H. (1995). The cobalt, zinc, and cadmium efflux system czcabc from Alcaligenes eutrophus functions as a cation-proton antiporter in Escherichia coli. J. Bacteriol. 177, 2707-2712. 

However, recent research proved the presence of a number of transporters in the cornea and conjunctiva such as amino acid/peptide, nucleoside, organic anionic and organic cationic. These systems will influence the absorption of active molecules. Moreover active substance efflux pumps at the cell surface could restrict active substance penetration into ocular tissues [5]. 

Nies DH (1994) Expression of the cobalt, zinc, and cadmium efflux system of Alcaligenes eutrophus in Escherichia coli CzcABC is a cation-proton antiporter. Eur J Biochem (submitted)... 

Sedgwick, E. G. Bragg, P. D. The role of efflux systems and the cell envelope in fluorescence changes of the lipophilic cation 2-(4-dimethy-laminostyryl)-l-ethylpyridinium in Escherichia coli. Biochim. Biophys. Acta 1996, 1278, 205-212. 

Evidence from a number of systems suggests that ion flux plays a role in palytoxin action. In a wide range of systems, palytoxin effects are accompanied by a change in intracellular cation levels. For example, the influx of Na and/or Ca is associated with palytoxin-stimulated contraction of cardiac and smooth muscle, the release of norepinephrine by rat pheochromocytoma (PC12) cells, and the depolarization of excitable membranes 12—15). Palytoxin also induces K efflux from erythrocytes and thus alters ion flux in a nonexcitable membrane system as well 16-19). In both excitable and nonexcitable membranes, the ultimate action of palytoxin has been shown to be dependent on extracellular cations. The palytoxin-induced effects on smooth muscle and erythroctyes can be inhibited by removing Ca from the media, and the palytoxin-induced release of norephinephrine from PC12 cells can be blocked in Na" free media (ii, 14y 18, 20, 21)... 

Phase 4 Hyperpolarization occurs before K+ efflux has completely stopped and is followed by a gradual drift towards threshold (pacemaker) potential. This is reflects a Na+ leak, T-type Ca2+ channels and a Na+/Ca2+ pump, which all encourage cations to enter the cell. The slope of your line during phase 4 is altered by sympathetic (increased gradient) and parasympathetic (decreased gradient) nervous system activity. 

Carrier-mediated membrane transport proteins on the RPE selectively transport nutrients, metabolites, and xenobiotics between the choriocapillaris and the cells of the distal retina, and include amino acid [33 35], peptide [36], dicarboxylate, glucose [37], monocarboxylic acid [38,39], nucleoside[40], and organic anion and organic cation [41] transporters. Membrane barriers such as the efflux pumps, including multidrug resistance protein (P-gp), and multidrug resistance-associated protein (MRP) pumps have also been identified on the RPE. Exploitation of these transport systems may be the key to circumventing the outer BRB. 

The redox system does not depend on endosomal acidification but needs TfR. Fe2Tf first binds to TfR which is located in close proximity to the proton-and electron-pumping NADHiTf oxidoreductase. The Fe—Tf bond is destabilized by proton efflux, making Fe3+ susceptible to reduction. Fe2+ is trapped by a plasma membrane binder and can be transported by a translocator [4]. As Al is a simple trivalent cation incapable of redox changes, it may be theoretically impossible that Al bound to Tf is taken up by a redox mechanism. Actually, no reports on a redox-mediated process of Al bound to Tf have been made. 

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