Interaction of intestinal brush border membrane vesicles with small unilamellar phospholipid vesicles. Exchange of lipids between membranes is mediated by collisional contact

Abstract

The kinetics of lipid transfer from small unilamellar vesicles as the donor to brush border vesicles as the acceptor have been investigated by following the transfer of radiolabeled or spin-labeled lipid molecules in the absence of exchange protein. The labeled lipid molecules studied were various radiolabeled and spin-labeled phosphatidylcholines, radiolabeled cholesteryl oleate, and a spin-labeled cholestane. At a given temperature and brush border vesicle concentration similar pseudo-first-order rate constants (half-lifetimes) were observed for different lipid labels used. The lipid transfer is shown to be an exchange reaction leading to an equal distribution of label in donor and acceptor vesicles at equilibrium (time t----infinity). The lipid exchange is a second-order reaction with rate constants being directly proportional to the brush border vesicle concentration. The results are only consistent with a collision-induced exchange of lipid molecules between small unilamellar phospholipid vesicles and brush border vesicles. Other mechanisms such as collision-induced fusion or diffusion of lipid monomers through the aqueous phase are negligible at least under our experimental conditions.

Spontaneous lipid transfer between organized lipid assemblies

“…Then, two different laboratories both reported increased spontaneous lipid transfer rates attributable to transient collisions between donor and acceptor surfaces [96][97][98][107][108][109]. Although similar claims had been reported previously [22,113], it was difficult to rule out fusion between vesicles [113] and protein-mediated lipid transfer [22,137] in these earlier reports.…”

“…12-16), with spinlabeled lipids (e.g., Refs. [17][18][19][20][21][22]. and with lipids bearing fluorescent dyes (e.g., [23][24][25][26][27][28][29][30].…”

Influence of class B scavenger receptors on cholesterol flux across the brush border membrane and intestinal absorption

“…The time courses describing the equilibration of radiolabel between the SUV and BBMV were analyzed as described previously ( 43 ); the kinetic equations account for the bidirectional fl ux of cholesterol between the donor and acceptor particles.…”

Intestinal absorption and biomagnification of organic contaminants in fish, wildlife, and humans

“…A pH decrease within the UWL adjacent to the brush border membrane (BBM) is believed to cause dissociation of the micelles, which then results in fatty acids and xenobiotics (e.g., PCBs) separating from the micelles and permeating through the water phase into the BBM of the epithelial cells as monomers [49]. However, some evidence suggests that collisional contact of mixed micelles and intestinal cell membranes causes release of lipids and chemical directly into the BBM [50]. The significance of the latter process is that it would essentially eliminate the resistance to membrane transfer posed by the aqueous diffusion barrier adjacent to the BBM and bypass diffusion altogether.…”

“…Numerous reviews of lipid absorption and digestive physiology have been conducted [47–51]. Figure 2 depicts the transcellular migration path of dietary fats and environmental contaminants (i.e., xenobiotics) from lumen across the epithelium of the gut wall.…”