Potassium ions Transport through membranes

The change in the absorption spectrum and the molecular structure on photoisomerization of azobenzenes can be used for practical applications. The literature on possible applications in photoresponsive materials was reviewed up to 1988 by Rau. Important contributions by Japanese workers, for example, on light-driven potassium ion transport through membranes by means of crown ethers with a photofunctional azobenzene cap, were recently summarized by Shinkai. Moreover, light-manipulation of other super molecules based on azobenzene photoisomerization is described in the book by Feringa. " The E— Z photoisomerization for the preparation of thermally unstable Z-isomers for use as kinetic probes in microheterogeneous media was described in Section 89.5. 

Sodium/Potassium pump - ion transport through membranes and ion channels... 

An essential requirement for diffusion of Na+ ions is the creation of a concentration gradient for sodium between the filtrate and intracellular fluid of the epithelial cells. This is accomplished by the active transport ofNa+ ions through the basolateral membrane of the epithelial cells (see Figure 19.4). Sodium is moved across this basolateral membrane and into the interstitial fluid surrounding the tubule by the Na+, K+-ATPase pump. As a result, the concentration of Na+ ions within the epithelial cells is reduced, facilitating the diffusion of Na+ ions into the cells across the luminal membrane. Potassium ions transported into the epithelial cells as a result of this pump diffuse back into the interstitial fluid (proximal tubule and Loop of Henle) or into the tubular lumen for excretion in the urine (distal tubule and collecting duct). 

Sodium and potassium activated adenosine triphosphatase (Na,K - ATPase) exists In plasma membrane and actively transports sodium Ions extracellularly and potassium Ions Intracellularly through the membrane as a cation pump. 

Potassium ion secretion. Potassium ions are secreted in the distal tubule and the collecting duct. These ions diffuse down their concentration gradient from the peritubular capillaries into the interstitial fluid. They are then actively transported up their concentration gradient into the tubular epithelial cells by way of the Na+, K+ pump in the basolateral membrane. Finally, potassium ions exit the epithelial cells by passive diffusion through K+ channels in the luminal membrane and enter tubular fluid to be excreted in the urine. 

The transport of hydrated sodium and potassium ions through the cell membrane is slow, and this transport requires an expenditure of energy by the cell. 

There is reason to beheve that cardiac glycosides, like other inotropic substances, act on the contractibility of the heart by affecting the process of calcium ion transfer through the membrane of myocardiocytes. The effect of cellular membranes in electric conductivity is mediated by transport of sodium, calcium, and potassium ions, which is a result of indirect inhibitor action on the (Na+-K+) ATPase of cell membranes. 

Kirch and Lehn have studied selective alkali metal transport through a liquid membrane using [2.2.2], [3.2.2], [3.3.3], and [2.2.C8] (146, 150). Various cryptated alkali metal picrates were transported from an in to an out aqueous phase through a bulk liquid chloroform membrane. While carrier cation pairs which form very stable complexes display efficient extraction of the salt into the organic phase, the relative rates of cation transport were not proportional to extraction efficiency and complex stability (in contrast to antibiotic-mediated transport across a bulk liquid membrane). Thus it is [2.2.Ca] which functions as a specific potassium ion carrier, while [2.2.2] is a specific potassium ion receptor (Table VI). 

Cystic fibrosis—a fatal, hereditary disease characterized by a heavy mucus buildup in the lungs—is caused by a defective plasma membrane protein. In persons with cystic fibrosis this transport protein, known as the sodium-potassium pump, abnormally transports sodium ions across the membrane without carrying the chloride ions that usually accompany them. Research is currently underway to correct through genetic engineering the faulty gene that codes for the plasma membrane protein. 

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