Diffusion exchange

The uptake and loss by exchange diffusion is important for aquatic organisms but not for terrestrial ones. 

Exchange diffusion systems are present in the membrane for exchange of anions against OH ions and cations against H ions. Such systems are necessary for uptake and output of ionized metaboUtes while preserv-... 

Fisher, J.F. and Cho, A.K., Chemical release of dopamine from striatal homogenates evidence for an exchange diffusion model, J. Pharmacol. Exp. Ther., 208, 203, 1979. 

Substitutional impurities can move by way of a number of mechanisms. The most usual is the vacancy mechanism described above. Diffusion studies on semiconductors have suggested that a number of additional mechanisms might hold. As well as vacancy diffusion, an impurity can swap places with a neighboring normal atom, exchange diffusion, while in ring diffusion cooperation between several atoms is... 

Figure 5-29 Schematic exchange diffusion profiles between (a) two large minerals and (b) a small olivine inclusion and its garnet host. The dashed lines are the assumed initial concentration distribution, and the solid curves are the resulting concentration distribution at present.

Barrer R.M., Bartholomew R.F., and Rees L.V.C. (1963) Ion exchange in porous crystals, II the relationship between self- and exchange-diffusion coefficients. /. Phys. Chem. Solids 24, 309-317. 

Organelles within cells have their own ion-concentrating mechanisms. Thus, mitochondria can concentrate K+, Ca2+, Mg2+, and other divalent metal ions as well as dicarboxylic acids (Chapter 18). The entrance and exit of many substances from mitochondria appear to occur by exchange diffusion, i.e., by secondary active transport. Such ion exchange processes may also occur in other membranes. 

The various proposed components of the permease system are based upon the response of the transport system to genetic or environmental changes. The complex nature postulated for the intact permease system is necessary to account for the various observed phenomena such as facilitated diffusion, active concentration, facilitated efflux, exchange diffusion, and counter transport of one compound driven by the downhill efflux of a second (2). 

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