Interactions between biliary lipid micelles and intestinal brush border membranes investigated by 1H and 31P nuclear magnetic resonance

Abstract

The effect of taurocholate and lecithin-cholesterol-taurocholate mixed micelles on the structure of isolated intestinal brush border membranes was investigated by nuclear magnetic resonance (NMR). Rabbit brush border membranes isolated by a Mg2+ precipitation step were chosen for this study because of their stability and integrity as revealed by 31P NMR. Incubation of taurocholate with the brush border membranes does not induce significant solubilization of these membranes even when the taurocholate/phospholipid ratio reaches 3.0. 1H NMR studies indicate that taurocholate is included in the membrane bilayer at low concentration (3 mM). However this biliary salt produces a size diminution of the vesicles when its concentration increases. Incorporation of lecithin or lecithin-cholesterol in micelles of taurocholate and subsequent incubation with brush border membranes lead simultaneously to a decrease in the 31P NMR isotropic/bilayer line ratio, and to an increase in delta sigma. These results indicate a protective effect of these compounds against lytic damage of taurocholate. Furthermore the equilibrium distribution of lecithin between mixed micelles and the membrane bilayer is strongly in favour of complete integration of micellar components in the bilayer. These data suggest that uptake of lipids from the micellar phase by isolated brush border membranes involves an interaction of the micelles with membranes followed by a fusion process.

Static and magic angle spinning 31P NMR spectroscopy of two natural plasma membranes

“…For over two decades, a substantial amount of knowledge, largely acquired with NMR methods, has been accumulated on the structural and dynamic properties of phospholipids in model membranes [1–12]. Conversely, very few studies have been undertaken using phospholipids in their natural plasma membrane environment [13–16]. As the protein‐membrane interactions occurring in the membrane environment raise a major challenge for understanding the wide range of cellular processes (for review see [12]), new investigation methods are needed to analyse structurally intact natural membranes.…”

“…Very few static studies have been undertaken on natural membranes [13–16]; spectra obtained are characteristic of the bilayer configuration and often have a narrow component as observed in phospholipid‐protein systems [9–11]. However, these studies were principally performed on organelle membranes which have a significantly lower cholesterol content than plasma membranes.…”

Biochemistry of Antioxidants: Mechanisms and Pharmaceutical Applications

“…This is, for example, how low-density lipoproteins are delivered to cells. However, some vesicles, such as mixed micelles, obtained during lipid digestion containing phospholipids, cholesterol, fatty acids and other dietary molecules such as tocopherol and carotenoids are able to deliver their content by fusing with the enterocyte membrane without the need for a specific recognition [ 71 ].…”