Membranes cation transport

Investigations of the cellular effects of radiofrequency radiation provide evidence of damage to various types of avian and mammalian cells. These effects involve radiofrequency interactions with cell membranes, especially the plasma membrane. Effects include alterations in membrane cation transport, Na+/K+-ATPase activity, protein kinase activity, neutrophil precursor membrane receptors, firing rates and resting potentials of neurons, brain cell metabolism, DNA and RNA synthesis in glioma cells, and mitogenic effects on human lymphocytes (Cleary 1990). 

Kimura, K., Sakamoto, H., Koseki, Y., Shono, T., Excellent, ph-sensitive cation-selectivities of bis(monoazacrown ether) derivatives in membrane cation-transport, Chem. Lett., 1241-1244,1985. 

Kaplan JG (1978) Membrane cation transport and the control of proliferation of mammalian cells. Annu Rev Physiol 40 16-35... 

Rozendal, R.A., Hamelers, H.V M. Buisman, C.J.R Effects of membrane cation transport on pH and microbial fuel-cell performance. Environ. Sci. Technol. 40 (2006), pp. 5206-5211. 

Table 4. Amounts of cation transported by the synthetic ionophores through chloroform liquid membrane after 2 days...

On the other hand, Bartsch et al. have studied cation transports using crown ether carboxylic acids, which are ascertained to be effective and selective extractants for alkali metal and alkaline earth metal cations 33-42>. In a proton-driven passive transport system (HC1) using a chloroform liquid membrane, ionophore 31 selectively transports Li+, whereas 32-36 and 37 are effective for selective transport of Na+ and K+, respectively, corresponding to the compatible sizes of the ring cavity and the cation. By increasing the lipophilicity from 33 to 36, the transport rate is gradually... 

The Energetics Problem of Cation Transport Across Lipid Bilayer Membranes A qualitative perspective of the barrier presented by a lipid bilayer membrane can be obtained from the Bom expression2) for solvation energy, SE,... 

The organic cation transporters (OCTs) facilitate the uptake of many cationic drugs across different barrier membranes from kidney, liver, and intestine... 

X-ray diffraction studies on gramicidin commenced as early as 1949 218-219> and this early work pointed to a helical structure 220). Recent work by Koeppe et al. 221) on gramicidin A crystallised from methanol (/%) and ethanol (.P212121) has shown that the helical channel has a diameter of about 5 A and a length of about 32 A in both cases. The inclusion complexes of gramicidin A with CsSCN and KSCN (P212121) have channels that are wider (6-8 A) and shorter (26 A) than the uncomplexed dimer 221 222). Furthermore there are two cation binding sites per channel situated either 2.5 A from either end of the channel or 2.5 A on each side of its centre 222) Unfortunately these data do not permit a choice to be made from the helical models (i)—(iv) and it is not certain if the helical canals studied are the same as those involved in membrane ion transport. 

Figure 8.3 A model of iron transport across the intestine. Reduction of ferric complexes to the ferrous form is achieved by the action of the brush border ferric reductase. The ferrous form is transported across the brush border membrane by the proton-coupled divalent cation transporter (DCT1) where it enters an unknown compartment in the cytosol. Ferrous iron is then transported across the basolateral membrane by IREG1, where the membrane-bound copper oxidase hephaestin (Hp) promotes release and binding of Fe3+ to circulating apotransferrin. Except for hephaestin the number of transmembrane domains for each protein is not shown in full. Reprinted from McKie et al., 2000. Copyright (2000), with permission from Elsevier Science.

Meyer-Wentrup F, Karbach U, Gor-boulev V, Arndt P, Koepsell H. Membrane localization of the electrogenic cation transporter rOCTl in rat liver. Bio-chem Biophys Res Commun 1998 248(3) 673-678. 

The effects of Li+ upon hematopoiesis have been proposed to be due to two different systems modification of the activity of the membrane Na+/K+-ATPase, and the inhibition of adenylate cyclase. Monovalent cation flux, in particular Na+ transport, is known to influence the differentiation and proliferation of hematopoietic stem cells. For instance, ouabain, an effective inhibitor of the membrane Na+/K+-ATPase, blocks the proliferation of lymphocytes and has been shown to attenuate the Li+-induced proliferation of granulocyte precursors [208]. Conversely, Li+ can reverse the actions of amphotericin and monensin, which mediate Na+ transport and which inhibit CFU-GM, CFU-E, and CFU-MK colony formation in the absence of Li+ [209]. Therefore, the influence of Li+ upon normal physiological cation transport—for example, its influence upon Na+/K+-ATPase activity—may be partly responsible for the observed interference in hematopoiesis. 

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