Rapid transport protein modulation

Direct use of endothelin is not practical for clinical purposes. However, this signaling pathway shows a way that might be useful to manipulate P-glycoprotein and to help in the short term to treat patients with P-glycoprotein substrates that do not cross the blood-brain barrier. 

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The transport processes and biological response involved in quinone-stimulated human epithelial cells were further studied by Rotenberg and Mirkin. They demonstrated that quinone-based mediators rapidly cross the cell wall to electrochemically react in the intracellular lumen. These events are reported to occur on a microsecond timescale. The apparent electron transfer rates measured for nonmetastatic and metastatic cells demonstrate the modulation effects of protein kinase Ca. Such studies establish the potential for SECM to evolve in an analytical tool capable of discriminating between cancerous and healthy cells. As such, the judicious choice of redox mediator couple will be key in achieving the desired electrochemical contrast. ... 

Selenium is readily absorbed, especially in the duodenum but also in the caecum and colon. Seleno-amino acids are almost completely absorbed selenomethionine via the gut methionine transporter and selenocysteine probably via the cysteine transporter. Both selenite and selenate are >50% absorbed, selenite more readily so than selenate, and for these forms there is competition with sulphate transport. Selenite is more efficiently retained then selenate because part of the latter is rapidly excreted into the urine. Vitamins A, E, and C can modulate selenium absorption, and there is a complex relationship between selenium and vitamin E that has not been entirely elucidated for man. A combined deficiency of both nutrients can produce increases in oxidative damage markers (malondialdehyde, Ei isoprostanes, and breath hydrocarbons) and in pathological changes that are not seen with either deficiency alone. Inorganic Se is reduced to selenide by glutathione plus glutathione reductase and is then carried in the blood plasma, bound mainly to protein in the very low-density lipoprotein fraction. Selenomethionine is partly carried in the albumin fraction. 

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