Differential effects induced by α- and β-endosulfan in lipid bilayer organization are reflected in proton permeability

• Published in: Biochimica et biophysica acta 2002-08, Vol.1564 (1), p.140-148
• Main Authors: Videira, Romeu A, Antunes-Madeira, Maria C, Madeira, Vı́tor M.C
• Format: Article
• Language: English
• Subjects: 1,2-Dipalmitoylphosphatidylcholine - chemistry; Endosulfan - chemistry; Endosulfan - toxicity; Hydrocarbons, Chlorinated; In Vitro Techniques; Insecticides - chemistry; Insecticides - toxicity; Isomerism; Lipid Bilayers - chemistry; Lipid vesicle; Liposomes - chemistry; Membrane organization; Permeability - drug effects; Proton permeability; Protons; Spectrometry, Fluorescence; α-Endosulfan; β-Endosulfan
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/S0005-2736(02)00441-8

The effects of two insecticides isomers, α- and β-endosulfan, on the passive proton permeability of large unilamellar vesicles (LUV) reconstituted with dipalmitoylphosphatidylcholine (DPPC) or mitochondrial lipids were reported. In DPPC (LUV) gel phase, at 30 °C, the global kinetic constant ( K) of proton permeability (proportional to the proton permeability) initially increased slightly with the increase of α-endosulfan/lipid molar ratio up to 0.143. In the range from 0.143 to 0.286, a discontinuity in the increment occurred and, above this range, the proton permeability increased substantially. In DPPC fluid phase, at 48 °C, the proton permeability showed a behavior identical to that observed in gel DPPC, with a sharp increase for α-endosulfan/lipid molar ratios ranging from 0.143 to 0.286. At these and higher concentrations, α-endosulfan induced phase separation in the plane of DPPC membranes, as revealed by differential scanning calorimetry (DSC). Conversely to α-endosulfan, β-endosulfan induced only a slight increase in the proton permeability, either in the fluid or the gel phase of DPPC, for all β-endosulfan/lipid molar ratios tested. Additionally, the effects of the endosulfan isomers on the proton permeability of mitochondrial fluid lipid dispersions, at 37 °C, are similar to those described for DPPC. The β-isomer induced a very small effect, and α-endosulfan, at low concentrations, increased slightly the proton permeability, but for insecticide/lipid molar ratios above 0.143 the permeability increased substantially. Consequently, the membrane physical state of synthetic and native lipid dispersions, as affected by the structural features of α- and β-endosulfan, influenced the proton permeability. The effects here observed in vitro suggest that the formation of lateral membrane domains may underlay the biological activity of α-endosulfan in vivo, contributing to its higher degree of toxicity as compared with β-endosulfan.