title: A novel method for the efficient entrapment of calcium in large unilamellar phospholipid vesicles.
abstract: A technique for the efficient entrapment of high concentrations of Ca2+ in large unilamellar phospholipid vesicles (LUVs), using the carboxylic acid antibiotic ionophore A23187 (calcimycin) is demonstrated. It is shown that rapid A23187-mediated entrapment of Ca2+, corresponding to essentially 100% sequestration of the extravesicular cation may be achieved for egg yolk phosphatidylcholine LUVs (100 nm) in the presence of a transmembrane proton gradient (acidic interior). Interior-exterior concentration cation gradients of over 400-fold may be readily achieved, with interior Ca2+ concentrations in excess of 250 mM. It is shown that the extent and efficiency of the A23187-mediated uptake process is affected by the intravesicular buffering capacity and the extravesicular Ca2+ concentration in a manner that is consistent with a Ca2(+)-H+ exchange process. In the absence of a pH gradient, or the presence of a reversed gradient (basic interior), only background levels of cation uptake are detected. The driving force for A23187-mediated uptake of Ca2+ is shown to depend on the intravesicular proton pool rather than on a chelation process. This protocol provides a novel method for the efficient entrapment of high concentrations of Ca2+ and other cations in phospholipid vesicles.
authors.affiliation: Department of Biochemistry, University of British Columbia, Vancouver, Canada.
authors.forename: J A
authors.initials: JA
authors.lastname: Veiro
authors.forename: P R
authors.initials: PR
authors.lastname: Cullis
mesh_terms: D001692:Biological Transport; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism
chemical_list: D010713:Phosphatidylcholines; D000001:Calcimycin; D002118:Calcium