Improved membrane fluidity of ionic polysaccharide bead-supported phospholipid
bilayer membrane systems
ABSTRACT
Supported phospholipid bilayer membranes on polysaccharide-based cationic
polymer beads (cationic group: –[OCH2CH(OH)CH2]2N+(CH3)3·X−, 45–165 m in diameter) were prepared using small unilamellar vesicles
from mixtures of phosphatidylserine (PS) and phosphatidylcholine (PC).
Confocal fluorescence microscopic observations with a fluorescent membrane
probe (N-4-nitrobenzo-2-oxa-1,3-diazole-phosphatidylethanolamine) revealed
that the phospholipid molecules in the phospholipid-bead complexes were
along the outer surface of the beads. The fluidity of the phospholipid
bilayer membranes in the PS/PC-bead complexes was investigated by the fluorescence
recovery after photobleaching (FRAP) technique. The lateral diffusion coefficients
(D) for the PS/PC-bead complexes were lower than that for the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine
giant unilamellar vesicles without solid supports. Such less fluid membranes
in the complexes appeared to be due to the immobilization of the phospholipid
bilayer membranes by electrostatic attractive forces between PS and the
bead. The D values for the PS/PCbead complexes were dependent on the phospholipid
composition; the PS(100 mol%)/PC(0 mol%)-bead complex had the least fluid
membranes among the PS/PC-bead complexes tested in this study. The phospholipid
bilayer membranes formed on the polysaccharide-based cationic polymer beads
were much more fluid than those on a polystyrene-based one. Furthermore,
such fluid phospholipid bilayer membranes formed on the polysaccharide-based
cationic polymer bead were maintained for 10 days, even though the complex
sample was stood in plain buffer (pH 8.5) at ambient temperature.