Translational diffusion of lipids in liquid crystalline phase phosphatidylcholine multibilayers. A comparison of experiment with theory.

A systematic study of the translational diffusion of the phospholipid derivative N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (NBD-PE) has been undertaken in liquid crystalline phase phosphatidylcholine bilayers by using the fluorescence recovery after photobleaching technique. This work was done with the intention of comparing the experimental results with the predictions of theoretical models for diffusion in membranes. The following is shown. For NBD-PE, the dependence of the translational diffusion coefficient (Dt) upon the acyl chain length of the diffusant is not that predicted by continuum fluid hydrodynamic models for diffusion in membranes [Saffman, P.G., & Delbrueck, M. (1975) Proc. Natl. Acad. Sci. U.S.A. 72, 3111-3113; Hughes, B. D., Pailthorpe, B. A., & White, L. R. (1981) J. Fluid Mech. 110, 349-372]. Plots of Dt vs. 1/T (Arrhenius plots) are nonlinear in dilauroyl-phosphatidylcholine (DLPC), dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) bilayers where the acyl chain composition of the NBD-PE is matched with that of the host bilayer lipid. This suggests that a "free volume" model may be appropriate for the description of lipid diffusion in lipid bilayers. In bilayers of phosphatidylcholines with saturated acyl chains at the same "reduced temperature", the magnitude of Dt follows the order distearoylphosphatidylcholine greater than DPPC greater than DMPC greater than DLPC. This is the inverse of what may be expected from the hydrodynamic model but is in agreement with the free volume in these bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)