Lateral diffusion in phospholipid multibilayers measured by fluorescence recovery after photobleaching

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.