Curvature elasticity of multilamellar lipid bilayers close to the chain-melting transition

We directly measured curvature elasticity of dipalmitoylphosphatidylcholine multilamellar bilayers close to the chain-melting transition using the method of electric-field-induced bending deformation of the cylindrical tubes. The result shows that the bending modulus, k(c), decreases remarkably at temperatures close to the melting transition temperature. This reflects a softening of the bilayer resulted from the area fluctuations as predicted theoretically. However, the decrease of k(c) near the transition is far smaller than that predicted. This is due to the experimental method and the narrow transition width of the multilamellar bilayers. Nevertheless, the result obtained gives direct evidence of the k(c) reduction predicted for multilamellar membranes in the transition regime. Below about 41 degreesC, almost of all cylindrical tubes cannot response to the electric field, indicating a very large bending rigidity. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.