Cation antiporters

T. Terada, S. Masuda, J. Asaka, M. Tsuda, T. Katsura, and K. Inui. Molecular cloning, functional characterization and tissue distribution of rat H+/organic cation antiporter MATE1. Pharm Res 23 1696-1701 (2006). 

S. Masuda, T. Terada, A. Yonezawa, Y. Tanihara, K. Kishimoto, T. Katsura, O. Ogawa, and K. Inui. Identification and functional characterization of a new human kidney-specific H+/organic cation antiporter, kidney-specific multidrug and toxin extrusion 2. J Am Soc Nephrol 17 2127-2135 (2006). 

When incorporated into the phospholipid membrane of liposomes, compounds 114 and 115 increased the permeability to Na+ and Li+ ions, and ion transfer proceeded by a cation-cation antiport mechanism (Figure 25) [8.208]. 

H. Maegawa, M. Kato, K.-I. Inui, and R, Hori, pH sensitivity of H+/organic cation antiport system in rat renal brush-border membranes, /. Bin/. Chem., 263 11,150-11,154 (1988). 

Tanihara, Y., Masuda, S., Sato, T., Katsura, T., Ogawa, O. and Inui, K. (2007) Substrate specificity of MATEl and MATE2-K, human multidrug and toxin extrusions/H(+)-organic cation antiporters. Biochemical Pharmacology, 74, 359-371. 

In cardiac muscle cells a three-Na /one-Ca antiporter, rather than the plasma membrane Ca ATPase discussed earlier, plays the principal role in maintaining a low concentration of Ca in the cytosol. The transport reaction mediated by this cation antiporter can be written... 

In cardiac muscle cells, the export of Ca Is coupled to and powered by the import of Na by a cation antiporter, which transports 3 Na ions inward for each Ca Ion exported. 

The bouquet (91), incorporated into a phospholipid membrane of liposomes, increases the permeability of the membrane to Na" and Li. The ion transfer proceeds via a cation-cation antiport mechanism which has been established by Na and Li NMR spectroscopy <92AG(E)1637>. The incorporation of the bouquet molecule into several vesicular systems has been monitored by numerous techniques (UV, NMR, and CD spectroscopies, differential scanning calorimetry). It was concluded that different modes of incorporation take place and that several orientations of the bouquet coexist in the membranes <93JCS(P2)ioii>. 

Picrate salts are most convenient for the detection of cation/anion symport, which can be readily extended to the detection of cation antiport. The yellow picrate salts are added to the cis buffer, whereas a colorless salt is placed in the trans buffer. During cation antiport, picrate is transported as hydrophobic counteranion of the carrier-cation complex across the bulk membrane, and the increase in absorption of picrate in trans buffer readily indicates the velocity of the process. Caution Picrates are explosives they should be handled in small portions only.)... 

This simple technique is not applicable to ion channels that are too small or too selective to mediate the efflux of GMP. To detect the activity of ion channels with CD, the potassium selectivity of G-quartets can be used. For example, vesicles are loaded with GMP in the presence of potassium ions at concentrations above the dissociation constant ( Td) of G-quartets. In the presence of cation transporters, external cation exchange from potassium to cesium results in CD silencing as a resnlt of G-quartet disassembly within the vesicle in response to potassium ion efflux. Reversal of the direction of cation antiport with Cs-loaded vesicles and external potassium is even more attractive because the response to ion channel activity is chirogenic. This is one of the few methods where transport across and intactness of spherical membranes are simultaneously reported without additional effort (Section 4.1). 

The Ca H or Na cation antiporters (CaCA family) (Lytton 2007) are similarly represented in actinobacteria. Gram (-) bacteria, and archaea, but non-LAB firmicutes have substantially reduced numbers, and LAB lack these carriers altogether. These porters function primarily to exclude cytoplasmic Ca, but some of them can also export other divalent ions. In the next section we shall... 

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