Channel-forming agents

Some linear peptides such as the gramicidins A, B, and C, alamethicin, suzukacillin, and trichotoxin A-40 do not act as carriers but they form transmembrane channels across which alkali metal ions can migrate. Just as the carrier cavities, these channels display a hydrophilic interior and a lipophilic exterior, but in contrast to the former they exhibit poor ion selectivity. Since no complete X-ray studies of any of these channel forming agents are available only few facts are known about their conformations. Therefore, they will not be treated in this review. 

Channel-forming agents Inhibitors of ATPase Inhibitors of the respiratory chain... 

Aluminum trichloride, a cheap, abundant waste product of the chemical industry, forms a gel under certain conditions with carbonates and on mixing with alkalies. Laboratory and field tests showed that aluminum trichloride can be used as a gel-forming agent for reducing the permeability of waterconducting channels [673]. 

Figure 19. (A) Monensin modified channel forming unit 15, negatively charged a,(o-bifunctional amphiphile 16a and neutral one 16b, capable of forming monolayered membrane and positively charged bolaamphiphiles 17 as a sealing agent of the channel. (B) Model of channel formation by 15 in the monolayered membrane composed of 16 and the proposed blocking mode by 17." ...

The absorption of sulfonylureas from the upper gastrointestinal tract is faidy rapid and complete. The agents are transported in the blood as protein-bound complexes. As they are released from protein-binding sites, the free (unbound) form becomes available for diffusion into tissues and to sites of action. Specific receptors are present on pancreatic islet P-ceU surfaces which bind sulfonylureas with high affinity. Binding of sulfonylureas to these receptors appears to be coupled to an ATP-sensitive channel to stimulate insulin secretion. These agents may also potentiate insulin-stimulated glucose transport in adipose tissue and skeletal muscle. 

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