Interaction of the herbicide atrazine with model membranes. II: Effect of atrazine on fusion of phospholipid vesicles

A triazine herbicide minisensor based on surface-stabilized bilayer lipid membranes

This work describes an electrochemical technique that is suitable for rapid and sensitive screening of the triazine herbicides simazine, atrazine, and propazine. Egg phosphatidylcholine and dipalmitoylphosphatidic acid (DPPA) were used for the formation of self-assembled bilayer lipid membranes supported on silver wire (s-BLMs). Evidence that BLMs could form on silver wires was collected by means of ellipsometry which was done to investigate samples consisting of lipids deposited on planar reflective silver films. The interactions of triazines with s-BLMs produced electrochemical ion current increases which reproducibly appeared within ∼10 s after exposure of the lipid membranes to the herbicides. The sensitivity of the response was maximized by use of BLMs composed of 35% (w/w) DPPA and by alteration of the phase distribution within membranes by the introduction of 1.0 mM calcium ions in bulk solution. The mechanism of signal generation could be a result of rapid adsorption of the triazine on the surface of s-BLMs with a consequent rapid reorganization of the electrostatics of the membrane. The magnitude of the current signal was linearly related to the herbicide concentration, which could be determined at the nanomolar level. The present triazine minisensor exhibited good mechanical stability and longevity (routinely over 48 h), reproducible response characteristics (i.e., sensitivity and response to a given concentration of triazine in solution), fast response times, and low detection limits. The sensor can be simply and reliably fabricated at low cost. Studies have shown high selectivity for triazines in the presence of insecticides and pesticides.

The local anesthetic tetracaine destabilizes membrane structure by interaction with polar headgroups of phospholipids

The effect of the local anesthetic tetracaine at less than 10 mM on the water permeability of the phospholipid membrane was examined using liposomes composed of various molar ratios of negatively charged cardiolipin to electrically neutral phosphatidylcholine by monitoring their osmotic shrinkage in hypertonic glucose solution at 30 degrees C. The concentration of tetracaine causing the maximum velocity of shrinkage of liposomes increased with increase in the molar ratio of cardiolipin. Tetracaine increased the zeta-potential of the negatively charged liposomal membrane toward the positive side due to the binding of its cationic form to the negatively charged polar headgroups in the membrane. The maximum velocity of water permeation induced by osmotic shock was observed at essentially the same tetracaine concentration giving a zeta-potential of the liposomal membrane of 0 mV. These concentrations were not affected by change in the sort of acyl-chain of phospholipids in the liposomes when their negative charges were the same. These results suggests that the membrane integrity is governed mainly by the electrical charge of phospholipid polar headgroups when phospholipid bilayers are in the highly fluid state, and that positively charged tetracaine molecules neutralize the negative surface charge, lowering the barrier for water permeation through phospholipid bilayers.

Evaluation of antiepileptic drug effect on membrane fluidity

Many drugs and chemicals have been shown to induce modifications of the physicochemical properties of cellular membranes. In this study we investigated the changes in fluidity of erythrocyte membrane from epileptic patients under different pharmacological treatments, with respect to healthy controls, by using trimethylammonium-1,6-diphenyl-1,3,5-hexatriene (TMA-DPH) fluorescence polarization. The increase in TMA-DPH fluorescence polarization values observed in epileptic patients indicated a decrease in membrane fluidity. Since the analysis of erythrocyte membrane composition did not reveal significant differences between the two groups studied, a correlation with membrane lipoperoxide content was tried, as different drugs and chemicals elicit in vivo alterations resulting in peroxidation of membrane lipids. Therefore the presence of peroxidation products in the blood and the possible correlation with membrane lipoperoxide were studied. Although a direct causal linkage cannot be proved we can hypothesize that exogenous compounds such as antiepileptic drugs could modify membrane fluidity by increasing membrane lipid peroxidation. Moreover the increase of peroxidative products in the blood could indicate that the peroxidative damage might propagate through the formation of new free radical species. The possibility of using erythrocyte membrane as a model system to analyze antiepileptic drug side effects is advanced.