Interactions of surfactants with membranes and membrane components

3 Interactions of surfactants with membranes and membrane components 

The membranes were obtained and purified by standard procedures. They were resuspended in 0.25 M-sucrose/lOmM-Tris/HCl buffer, pH 7.4, to a concentration of 1 mg protein. Detergents were then added to obtain final concentrations between 0.1 and 1.0% (w/v), and the suspensions were incubated at 20° C for 30 min. Each preparation was centrifuged for 1 h at 1 SOOOOgav., at 4° C (Triton X-100 and deoxycholate treatments) or 18° C (sodium dodecyl sulphate). The supernatant was assumed to contain the solubilized fraction of the membranes. 

Fitzpatrick et al [29] have concluded that NaDS binds to all components of erythrocyte membranes uniformly release of components approximately follows the order of their water solubility, lipid solubilization occurring around the CMC of NaDS. About all the lipid is dissolved at lOmM. Between 2 and 10 mM NaDS (see Fig. 10.4) lipids are solubilized and form mixed micelles capable of solubilizing cholesterol. The exact sequence of events and nature of the comicelles, etc., has still to be elucidated. The authors found the Triton X-100 behaviour difficult to interpret. Although its CMC is 1 mmol 1 Mt is possible 

Such interactions are directly relevant to the effect of surfactants on drug absorption. Fig. 10.5a shows the relationship between absorption of salicylate or L-valine across rat jejunal tissue in vivo and release of protein and phospholipid by a series of surfactants. Fig. 10.5b shows the relative activity of a series of non-ionic surfactants of the Brij series and sodium taurodeoxycholic acid (NaTDC), sodium dodecyl sulphate (NaDS) and CTAB [30]. An association between protein release and increased absorption of solutes has also been reported by Feldman and Reinhard [31] and Walters et al. [32]. Anionic, non-ionic and cationic surfactants tended to accelerate the breakdown of the mucous layer covering the epithelium and at high concentrations were thought to interfere with the structure of the mucosal surface itself. Exposure of various anionic and nonionic surfactants to rabbit intestinal mucosa causes epithelial desquamation and necrosis [33]. 

Perfusion of 1 % NaDS at pH 7.4 in phosphate buffer caused great histological damage to the rat intestinal mucosa separation of the epithelium from the lamina 

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