EFFECTS OF DDE ON THE FLUIDITY OF MODEL AND NATIVE MEMBRANES - IMPLICATIONS FOR THE MECHANISMS OF TOXICITY

2,2-Bis(p-chlorophenyl)-1,1-dichloroethylene (DDE) interaction with mo del and native membranes was studied by means of fluorescence polariza tion of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and by intramolecular excimerization of 1,3-di(I-pyrenyl) propane (Py (3)Py), probing the outer regions of the bilayer. In the gel phase of DMPC bilayers, DDE induces concentration-dependent fluidizing effects into the hydrophobic core, but no effects are detected in the outer re gions of the membrane, as evaluated by DPH and Py(3)Py, respectively. Regarding the fluid phase, DDE has no apparent effect on the bilayer c enter, but it induces a limited ordering effect on the outer regions. Similar effects are described for bilayers of DPPC and DSPC. Unlike DP H, Py(3)Py is very sensitive to DPPC and DSPC pretransitions, not abol ished by DDE (50 muM), as opposite to the effects observed with lindan e (Antunes-Madeira, M.C., Almeida, L.M. and Madeira, V.M.C. (1990) Bio chim. Biophys. Acta 1022, 110-114), but similar to those observed with DDT (Antunes-Madeira, M.C., Almeida, L.M. and Madeira, V.M.C. (1991) Pestic. Sci. 33, 347-357). DDE inhibits to some extent the cholesterol -induced ordering in DMPC bilayers and high cholesterol concentrations (greater-than-or-equal-to 30 mol%) do not prevent DDE interaction, as evaluated by DPH. On the other hand, the effects of DDE reported by P y(3)Py depend on temperature and cholesterol contents of DMPC bilayers . For cholesterol levels ranging from 10 to 50 mol% and temperatures b elow the phase transition of DMPC, Py(3)Py fails to detect any signifi cant effect. Nevertheless, above the phase transition, Py(3)Py detects either ordering effects of DDE at low cholesterol contents ( < 30 mol %) or fluidizing effects at high cholesterol levels (greater-than-or-e qual-to 30 mol%). The results in native membranes correlate reasonably with those obtained in models of synthetic lipids. Thus, DPH does not detect any apparent effect of DDE in relatively fluid native membrane s of sarcoplasmic reticulum, but detects moderate disordering effects in membranes of brain microsomes and erythrocytes, i.e., membranes wit h high cholesterol. On the other hand, Py(3)Py reports ordering effect s of DDE in fluid membranes of sarcoplasmic reticulum, an effect simil ar to that observed in fluid systems of synthetic lipids without or wi th low cholesterol. Additionally, as described for models, Py(3)Py det ects disordering effects of DDE in cholesterol rich membranes, namely, brain microsomes.