A Mechanical Force Contributes to the “Osmotic Swelling” of Brush-Border Membrane Vesicles

Abstract

Brush-border membrane vesicles and an osmotic swelling assay have been used extensively to monitor the pore-forming activity of Bacillus thuringiensis toxins. After a hypertonic shock, Manduca sexta midgut brush-border membrane vesicles shrink rapidly and reswell partially to a volume that depends on membrane permeability and toxin concentration rather than regaining their original volume as expected from theoretical models. Because efflux of buffer from the vesicles, as they shrink, could contribute to this phenomenon, vesicles were mixed with a hypertonic solution of the buffer with which they were loaded. Under these conditions, they are not expected to reswell, since the same solute is present on both sides of the membrane. Nevertheless, with several buffers, vesicles reswelled readily, an observation that demonstrates the involvement of an additional restoration force. Reswelling also occurred when, in the absence of toxin, the buffers were replaced by glucose, a solute that diffuses readily across the membrane, but did not occur with rat liver microsomes, despite their permeability to glucose. Unexpected swelling was also observed with rabbit jejunum brush-border membrane vesicles, suggesting that the cytoskeleton, present in brush-border membrane vesicles but absent from microsomes, could be responsible for the restoration force.

Current models of the mode of action of Bacillus thuringiensis insecticidal crystal proteins: A critical review

“…This conclusion is very surprising in that it contradicts decades of work in this field. To cite only a few examples, in vitro trypsin-activated monomeric toxins do efficiently cause structural damage to the midgut epithelium (Bravo et al, 1992), permeabilize the plasma membrane of sensitive cultured insect cells (Guihard et al, 2000;Knowles and Ellar, 1987;Schwartz et al, 1991;Vachon et al, 1995;Villalon et al, 1998), abolish the membrane potential of freshly isolated insect midguts (Peyronnet et al, 1997), inhibit short-circuit currents generated across the isolated insect midgut epithelium (Chen et al, 1993;Liebig et al, 1995), permeabilize insect midgut brush border membrane vesicles (Carroll and Ellar, 1993;Coux et al, 2001;Kirouac et al, 2006a;Tigue et al, 2001) and inhibit amino acid transport into these vesicles (Sacchi et al, 1986;Wolfersberger, 1991). Moreover, most experiments comparing the permeabilization ability of pre-formed oligomers with that of monomers Muñoz-Garay et al, 2006;Pardo-López et al, 2006;Pérez et al, 2007;Rausell et al, 2004a,b,c) were done under conditions that allowed the monomeric toxins to pass through every step of the mechanism of pore formation, including possibly those described by the sequential model.…”

Effection of Lactic Acid Dissociation on Swelling-Based Short-Chain Fatty Acid Vesicles Nano-Delivery

“…The concentration of [H] produced by the change of pH was the most important factor for weak acid dissociation. According to the Gibbs–Helmholtz equation and the definition of K a , the dissociation constant ( pK a ), which directly reflects the dissociation ability of a compound in aqueous solution, is positively correlated with K a value [ 39 , 40 ]. The fact that solute molecules permeated into the vesicle implies that the vesicle progressively swells subsequently approaching a spherical shape; and its volume quickly readjusts through osmosis to change the number of enclosed solute molecules.…”

Multifusion-induced wall-super-thick giant multilamellar vesicles

“…It is known that vesicles shrink and then collapse or recover, depending on membrane permeability, when they are subject to osmotic stress. 5 Initially, when CS-PDEA vesicles were exposed to glucose solution, the volume of the vesicle did not change (data not shown). We attribute this to the good permeability of vesicles to glucose.…”