The Regulation of Membrane Fluidity in Schistosoma mansoni

The effect of serotonin on the fluidity of the tegumental membranes of adult male Schistosoma mansoni was assessed by the Fluorescence Recovery After Photobleaching technique . It is demonstrated that the translational diffusion of 5'-N-octadecanoyl aminofluorescein is reduced by a mechanism involving G-protein coupled activation of adenylate cyclase and lowering of intracellular calcium concentration. Furthermore, the lateral diffusion coefficient and the mobile fraction appear to be controlled by calcium and cAMP dependent pathways respectively. No change in the diffusion of the fluorescent phospholipid N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) phosphatidyl choline was observed, suggesting the two probes used here partition into two different domains that are under independent control. An increase in the amount of protein associating with a membrane cytoskeleton is also demonstrated. Part of this increase is due to the polymerisation of actin, which Is Important in the regulation of membrane fluidity. In its cytoskeletal form, this actin appears as a pentamer. Confocal microscopy also reveals that the tegumental actin radiates out from the tubercles, which are shown to have a hedgehog like arrangement of actin spines. It is also demonstrated that changes that occur in the cytoskeleton can have consequences for molecules that are expressed on the outer surface of the tegument, such as lipids, lectin receptors and antigens of host origin. One possible connection with the surface may occur via two proteins of molecular weights 48 and 52 kilo daltons