Vesicles pretransition

The effect of organophosphorous insecticides such as methylbromfenvinfos on membrane fluidity has been studied using the fluorescence anisotropy of 1,6-diphenyl-l,3,5-hexatriene (DPH), a probe known to be located in the hydrophobic core of the bilayer, and 1,3-bis (1-pyrene) propane (Py(3)Py), a probe distributed in the outer layer region [54]. DPH revealed a broadening of the transition profile and a solidifying effect in the fluid phase of DMPC and DPPC in the presence of 50 pM insecticide. An ordering effect of the insecticide in the fluid state was revealed by Py(3)Py. In addition, the pretransition in DPPC and DMPC vesicles was abolished by the insecticide. The addition of cholesterol decreased the influence of the insecticide. It was also observed that the influence on native membranes (erythrocytes, lymphocytes, brain microsomes, and sarcoplasmic reticulum) depended on the cholesterol content of the membranes. 

Dimova, R., Pouligny, B., and Dietrich, C. (2000) Pretransitional effects in dimyristoylphosphatidylcholine vesicle membranes optical dynamometry study. Biophysical Journal, 79 (1), 340-355. 

Fujiwara et al. [147] used DSC to follow the interactions between multilamel-lar vesicles of dipalmitoylphosphatidylcholine (1.4 mM) and polyacrylic acid as a function of pH. The thermograms showed the gradual disappearance of a small pretransition peak at 35 C and of the main transition peak (sharp) at 41°C, with the simultaneous appearance of a broad peak at 44°C as the pH was lowered from 7.6 to 3.8. At the latter pH value, only the 44°C peak was seen (Fig. 16). The peak at 41°C corresponds to pure vesicles, whereas the one at 44°C is due to the vesicles interacting with polyacrylic acid. The sum of the enthalpies of these peaks remained constant. Hence, the gel to liquid crystal transition tempera-... 

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