Mechanisms, ion transport

With the adequacy of lipid bilayer membranes as models for the basic structural motif and hence for the ion transport barrier of biological membranes, studies of channel and carrier ion transport mechanisms across such membranes become of central relevance to transport across cell membranes. The fundamental principles derived from these studies, however, have generality beyond the specific model systems. As noted above and as will be treated below, it is found that selective transport... 

Urry, D. W. On the Molecular Structure and Ion Transport Mechanism of the Gramicidin Transmembrane Channel. In Membranes and Transport, Vol. 2, (ed. Martonosi, A.), p. 285, Plenum Publishing Corporation, New York 1982... 

Fig. 2. Models for oxygen-ion transport mechanism over Ag-YSZ/CuO electrodes (a) at low overpotential, (b) at high overpotential [3].

The determination of the amino acid sequences of the sarcoplasmic reticulum Ca -ATPase [42] and of the closely related Na, K -ATPase [43,44] have opened a new era in the analysis of ion transport mechanisms. Since 1985, several large families of structurally related ion transport enzymes were discovered [3,34,45-50] that are the products of different genes. Within each family several isoenzymes may be produced from a single gene-product by alternative splicing (Table I). 

Oxidant Stress and the Heart Modulation of Ion Transport Mechanisms During Ischaemia and... 

R. H. Quinn and S. S. Miller. Ion transport mechanisms in native human retinal pigment epithelium. Invest Ophthalmol Vis Sci 33 3513-3527 (1992)... 

Liu, C. and Martin, C. R. 1990. Ion transporting membranes II. Ion transport mechanism in Nafion-rmpregnated Gore-Tex membranes. Journal of the Electrochemical Society 137 510-515. 

For the alkali metal cations, the stability (14) and permeability (43) sequences for dicyclohexyl-18-crown-6 have been found to be the same (K+ > Rb+ > Cs+ > Na+ > Li+). Thus, a direct relationship exists between the ability of a macrocyclic compound to complex a particular cation (as measured by the log K value for complex formation) and its influence on the biological transport of that cation. Furthermore, it would appear that the biological ion-transport mechanism may in part be due to the complexation properties of the macrocyclic carrier molecules. This subject with respect to cyclic antibiotics has been treated extensively by Si wow and co-workers (2). 

I assume, the membranes you are referring to are classical ion exchange membranes, the behavior of which is dictated to a large degree by charged groupings of the membrane material. The ion transport mechanism in such membranes is clearly not a carrier mechanism. 

Looking at the literature in the field of biomineralization, one notices, that the majority of articles is descriptive in nature. On the basis of electron micrographs or thin section studies, the intricate relationships between mineral phase and organic matrix are investigated. Other papers deal with the chemical composition of the mineralized tissue and the minerals. Only a few authors address themselves to the question of metal ion transport mechanisms in cellular systems and the solid state principles involved in mineral deposition on organic substrates. All three sets of information, however, are essential to understand calcification processes. It appears, therefore, that information on the functionality of metal ions in living systems and their role in mineral deposition are particularly desired in this area of research. 

Paugam, M.F. and Buffle, J. (1998) Comparison of carrier-facilitated copper (II) ion transport mechanisms in a supported liquid membrane and in a plasticized cellulose triacetate membrane. Journal of Membrane Science, 147, 207. 

Model systems have been developed for many of these ion-transport mechanisms in the context of bioorganic chemistry. Examples are the cyclic peptides, described by M. R. Ghadiri et al., that have antibiotic activity similar to that of ionophores, a property that is most probably caused by the ability of these peptides to self-assemble inside biological membranes into channels [1], Other compounds able to induce the formation of membrane pores are the bouquet-molecules introduced by J.-M. Lehn [2]. Artificial / -barrels have been developed by S. Matile s group [3]. Many host molecules used in bioorganic chemistry can serve as carriers for ions across membranes and have even made possible the development of systems with which active ion transport can be achieved [4]. 

Finally, it should be stressed that amiloride derivatives must be used with caution. They may affect a number of other ion transport mechanisms (e.g., the Na+/Ca2+ exchanger), or they may affect cellular activities (Cragoe et al., 1992), because of their weak base properties and capacity to accumulate in acidic intracellular compartments such as lysosomes. Amiloride derivatives may also be toxic to cells. 

Kourie, J. I. Interaction of reactive oxygen species with ion transport mechanisms. Am. J. Physiol. 275, Cl, 1998. 

In renewable-based energy systems PEM electrolysis seems to have an advantage over alkaline in that the thin membrane and ion transport mechanism can react to nearly instantaneously with the rapidly changing energy output of renewable sources, especially wind. Stacks involving the circulation of a liquid electrolyte have inherently more inertia in the transport of ions in solution than the PEM systems. 

To maintain electroneutrality during potassium secretion, the ion transport mechanism involves co-transport of K and Cl , as shown in Step 4, Details of the... 

Figure 8.29. Ion transport mechanisms through lipid membranes in living cells. There are principally two kinds of transport protein (a) channel proteins, that is, a channelforming ionophore, and (b) carrier proteins, that is, a mobile ion carrier ionophore. The phenomena observed in living cells have much in common with those in artificial polymer membrane ion-selective electrodes. (From Widmer, 1993.)...

It should be noted that the conductivity in ionic solids involves ion transport mechanism between coordinating sites (site-to-site hopping) and local structural relaxation. In general, the conductivity measured by ac measurements, can be expressed as a function of the conductivity from dc measurements, and the frequency (Bruce et al., 1983a,b Skinner and Munnings, 2002 Girdauskaite et al., 2006 Khrokunov et al., 2006 Berenov et al., 2007) ... 

Interestingly, the voltage-gated CLC has classic channel characteristics, whereas CFTR has characteristics of an ion channel and a carrier. Apparently, in the case of CLC, the classical definition for channels and carriers is mixed, suggesting that the two types of ion transport mechanisms share common features. 

Clearly many ion-transport mechanisms can be imagined having features of both carriers and channels. The experimental problem is one of making measurements of... 

We can also see that the measured activation energy reading on the semicircle we obtained at high frequencies is lower than the one we observed on the low frequency semicircle. This could mean that the ion transport mechanism functions with greater ease in the bulk than it enjoys at the grain boundaries. 

FIGURE 2.84 Illustration of ion transport mechanism in GO-PVA and GO-B-VA alkaline gel electrolytes with low and high GO content. (Reprinted from Electrochimica Acta. 132, Huang, Y. F. et al.. Boron cross-linked graphene oxide/polyvinyl alcohol nanocomposite gel electrolyte for flexible solid-state electric donble layer capacitor with high performance, 103-111, Copyright 2014, with permission from Elsevier.)... 

---