The properties of 4 fluorescent lipid compounds in the surface membrane of adult male Schistosoma mansoni worms were examined by fluorescent microscopy and fluorescent recovery after photobleaching (FRAP). The data suggest that the probes N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl) sphingosine (BODIPY FL ceramide) and PKH2 pass through the outer membrane and enter structures in or below the membrane. In contrast 5-(N-octadecanoyl)aminofluorescein (AF18) and N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl) sphingosylphosphocholine (BODIPY FL sphingomyelin) insert into the outer monolayer. The DL values of these latter 2 compounds, 8·83 ± 2·35 × 10−9 cm2 s−1 and 2·76 ± 0·53 × 10−9cm2 s−1, respectively, suggest that they enter different domains. Furthermore, it was observed that both BODIPY FL ceramide and BODIPY FL sphingomyelin entered particular structures in or under the surface membrane. The possible nature of these particles is discussed.
