A Time-Resolved Fluorescence Diphenylhexatriene (DPH) Anisotropy Characterization of a Series of Model Lipid Constructs for the Sperm Plasma Membrane

We present a steady-state and time-resolved fluorescence anisotropy analysis, using the probe diphenylhexatriene (DPH), of a hierarchical series of lipid membrane constructs that have been designed to resemble sperm plasma membranes. Anisotropy and lipid order parameters determined for the model membranes are compared to those of lipid membranes reconstituted from rabbit sperm plasma membranes. In addition, we study the response of all membrane systems to surfactant attack. The surfactants used in this investigation have current or potential use as spermicidal and antimicrobial agents. We show that our highest-level approximation of the sperm plasma membrane captures the essential characteristics of the sperm extract membranes, in terms of lipid order and response to surfactant attack. Our studies also highlight the importance of sphingomyelin as a regulator of membrane properties and also show indirect evidence of lateral phase separation in the membrane constructs that contain both cholesterol and sphingomyelin, as revealed by a preservation of lipid order under surfactant attack.