title: Effects of lipid composition and solution conditions on the mechanical properties of membrane vesicles.
abstract: The mechanical properties of cell-sized giant unilamellar liposomes were studied by manipulating polystyrene beads encapsulated within the liposomes using double-beam laser tweezers. Mechanical forces were applied to the liposomes from within by moving the beads away from each other, which caused the liposomes to elongate. Subsequently, a tubular membrane projection was generated in the tip at either end of the liposome, or the bead moved out from the laser trap. The force required for liposome transformation reached maximum strength just before formation of the projection or the moving out of the bead. By employing this manipulation system, we investigated the effects of membrane lipid compositions and environment solutions on the mechanical properties. With increasing content of acidic phospholipids, such as phosphatidylglycerol or phosphatidic acid, a larger strength of force was required for the liposome transformation. Liposomes prepared with a synthetic dimyristoylphosphatidylcholine, which has uniform hydrocarbon chains, were transformed easily compared with liposomes prepared using natural phosphatidylcholine. Surprisingly, bovine serum albumin or fetuin (soluble proteins that do not bind to membranes) decreased liposomal membrane rigidity, whereas the same concentration of sucrose showed no particular effect. These results show that the mechanical properties of liposomes depend on their lipid composition and environment.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. k614899x@m2.aichi-c.ed.jp.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Kato
authors.affiliation: Institute of Multidisciplinary, Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan. ishijima@tagen.tohoku.ac.jp.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Ishijima
authors.affiliation: Lipid Biology Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. takinaba@riken.jp.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Inaba
authors.affiliation: Department of Biomedical Information, Division of Biosystems, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda, Tokyo 101-0062, Japan. nomura.bmi@tmd.ac.jp.
authors.forename: Fumimasa
authors.initials: F
authors.lastname: Nomura
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. takeda.shuichi@f.mbox.nagoya-u.ac.jp.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Takeda
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan. j46037a@nucc.cc.nagoya-u.ac.jp.
authors.forename: Kingo
authors.initials: K
authors.lastname: Takiguchi