title: 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.
authors.affiliation: Membrane Protein Research Group, University of Montreal, Montreal, Quebec, Canada.
authors.forename: Martin
authors.initials: M
authors.lastname: Kirouac
authors.forename: Vincent
authors.initials: V
authors.lastname: Vachon
authors.forename: Mélanie
authors.initials: M
authors.lastname: Fortier
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Trudel
authors.forename: Alfred
authors.initials: A
authors.lastname: Berteloot
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Schwartz
authors.forename: Raynald
authors.initials: R
authors.lastname: Laprade
mesh_terms: D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000008:administration & dosage*; D001427:Bacterial Toxins / Q000008:administration & dosage*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004731:Endotoxins / Q000008:administration & dosage*; D006460:Hemolysin Proteins / Q000008:administration & dosage*; D008297:Male; D040542:Mechanotransduction, Cellular / Q000187:drug effects / Q000502:physiology*; D008560:Membrane Fluidity / Q000187:drug effects / Q000502:physiology*; D021962:Membrane Microdomains / Q000187:drug effects / Q000502:physiology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000502:physiology*; D008871:Microvilli / Q000187:drug effects / Q000502:physiology*; D009997:Osmotic Pressure; D051381:Rats; D017208:Rats, Wistar; D013314:Stress, Mechanical; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology*
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis