Lateral diffusion in phospholipid multibilayers measured by fluorescence recovery after photobleaching

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Abstract
The method of fluorescence recovery after photobleaching was used to measure the temperature dependence of the lateral diffusion coefficients (D) of 2 fluorescent lipid analogues in phospholipid multibilayers of various compositions. The probes employed were 3,3''-dioctadecyloxocarbocyanine (diO-C18(3)) and N-4-nitrobenz-2-oxa-1,3-diazole phosphatidylethanolamine (NBD-PE). In fluid egg phosphatidylcholine multibilayers at 25.degree. C, D was about 4 .times. 10-8 cm2/s for NBD-PE and 1.5 .times. 10-7 cm2/s for diO-C18(3) and was moderately temperature dependent (2-fold change over 10.degree. C). Equimolar cholesterol reduced D for NBD-PE in these multibilayers by a factor of 2. A greater than 100-fold decrease in D was detected in dimyristoylphosphatidylcholine multibilayers at approximately 23.degree. C, which coincides with the gel-to-liquid-crystalline transition temperature, Tm [melting temperature] (D .apprx. 5 .times. 10-8 cm2/s at T > Tm to D < 5 .times. 10-1O cm2/s at T < Tm). Equimolar cholesterol abolished this transition behavior, raising D below Tm and decreasing D above Tm. These results confirm and extend previous studies of lateral diffusion employing magnetic resonance and other optical techniques and give additional confidence in the fluorescence method.