Probing the critical unilamellar state of membranes.
Aqueous dispersions of membrane phospholipids comprised of multilamellar vesicles (MLVs) will spontaneously transform to a stable unilamellar structure equivalent to the membrane bilayer, but only at a critical temperature T*. Since much of the evidence for this transformation derives from equilibrium thermodynamic studies, a description of the molecular and topological events occurring as the critical unilamellar state assembles has not previously been possible. Here we report experiments that provide evidence of a spontaneous topological change from MLVs towards unilamellar vesicles (ULVs) at T*. By applying a shearing stress to vesicle suspensions we have observed a decrease of approximately 25% in the force required to cause bilayers to leak; this decrease is confined to temperatures near T*. The T* values observed agree with those previously obtained by equilibrium methods. Using the method with total lipid extracts from normal biological membranes confirms that T* equals the physiological temperature of the original membranes.
Gershfeld
N L
NL
Laboratory of Physical Biology, National Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH, Bethesda, MD, 20892, USA.
Ginsberg
L
L
D002462:Cell Membrane / Q000737:chemistry / Q000648:ultrastructure*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D008051:Lipid Bilayers; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D013314:Stress, Mechanical; D013816:Thermodynamics
D008051:Lipid Bilayers; D008081:Liposomes; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D004134:Dimyristoylphosphatidylcholine