publications by David Needham.

Papers Published

1. Olbrich, K. and Rawicz, W. and Needham, D. and Evans, E., Water permeability and mechanical strength of polyunsaturated lipid bilayers, Biophys. J. (USA), vol. 79 no. 1 (2000), pp. 321 - 7 .
   (last updated on 2007/04/06)

   Abstract:
   Micropipette aspiration was used to test mechanical strength and water permeability of giant-fluid bilayer vesicles composed of polyunsaturated phosphatidylcholine PC lipids. Eight synthetic-diacyl PCs were chosen with 18 carbon chains and degrees of unsaturation that ranged from one double bond (C18:0/1, C18:1/0) to six double bonds per PC molecule (diC18:3). Produced by increasing pipette pressurization, membrane tensions for lysis of single vesicles at 21°C ranged from ~9 to 10 mN/m for mono- and dimono-unsaturated PCs (18:0/1, 18:1/0: and diC18:1) but dropped abruptly to ~5 mN/m when one or both PC chains contained two cis-double bonds (C18:0/2 and diC18:2) and even lower ~3 mN/m for diC18:3. Driven by osmotic filtration following transfer of individual vesicles to a hypertonic environment, the apparent coefficient for water permeability at 21°C varied modestly in a range from ~30 to 40 μm/s for mono- and dimono-unsaturated PCs. However, with two or more cis-double bonds in a chain, the apparent permeability rose to ~50 μm/s for C18:0/2, then strikingly to ~90 μm/s for diC18:2 and ~150 μm/s for diC18:3. The measurements of water permeability were found to scale exponentially with the reduced temperatures reported for these lipids in the literature. The correlation supports the concept that increase in free volume acquired in thermal expansion above the main gel-liquid crystal transition of a bilayer is a major factor in water transport. Taken together, the prominent changes in lysis tension and water permeability indicate that major changes occur in chain packing and cohesive interactions when two or more cis-double bonds alternate with saturated bonds along a chain

   Keywords:
   biomechanics;biomembrane transport;biothermics;bonds (chemical);lipid bilayers;molecular biophysics;permeability;