Membrane fluidity as affected by the organochlorine insecticide DDT

Rafting on the Evidence for Lipid Raft-like Domains as Hubs Triggering Environmental Toxicants' Cellular Effects

The plasma membrane lipid rafts are cholesterol- and sphingolipid-enriched domains that allow regularly distributed, sub-micro-sized structures englobing proteins to compartmentalize cellular processes. These membrane domains can be highly heterogeneous and dynamic, functioning as signal transduction platforms that amplify the local concentrations and signaling of individual components. Moreover, they participate in cell signaling routes that are known to be important targets of environmental toxicants affecting cell redox status and calcium homeostasis, immune regulation, and hormonal functions. In this work, the evidence that plasma membrane raft-like domains operate as hubs for toxicants' cellular actions is discussed, and suggestions for future research are provided. Several studies address the insertion of pesticides and other organic pollutants into membranes, their accumulation in lipid rafts, or lipid rafts' disruption by polychlorinated biphenyls (PCBs), benzo[a]pyrene (B[a]P), and even metals/metalloids. In hepatocytes, macrophages, or neurons, B[a]P, airborne particulate matter, and other toxicants caused rafts' protein and lipid remodeling, oxidative changes, or amyloidogenesis. Different studies investigated the role of the invaginated lipid rafts present in endothelial cells in mediating the vascular inflammatory effects of PCBs. Furthermore, in vitro and in vivo data strongly implicate raft-localized NADPH oxidases, the aryl hydrocarbon receptor, caveolin-1, and protein kinases in the toxic mechanisms of occupational and environmental chemicals.

Neurotoxic and Neuroprotective Role of Exosomes in Parkinson’s Disease

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Exosomes are extracellular vesicles produced by eukaryotic cells that are also found in most biological fluids and tissues. While they were initially thought to act as compartments for removal of cellular debris, they are now recognized as important tools for cell-to-cell communication and for the transfer of pathogens between the cells. They have attracted particular interest in neurodegenerative diseases for their potential role in transferring prion-like proteins between neurons, and in Parkinson’s disease (PD), they have been shown to spread oligomers of α-synuclein in the brain accelerating the progression of this pathology. A potential neuroprotective role of exosomes has also been equally proposed in PD as they could limit the toxicity of α-synuclein by clearing them out of the cells. Exosomes have also attracted considerable attention for use as drug vehicles. Being nonimmunogenic in nature, they provide an unprecedented opportunity to enhance the delivery of incorporated drugs to target cells. In this review, we discuss current knowledge about the potential neurotoxic and neuroprotective role of exosomes and their potential application as drug delivery systems in PD.

Studies on the contributions of smoke constituents, individually and in mixtures, in a range of in vitro bioactivity assays

Tobacco smoke is a complex mixture with over 8700 identified constituents. Smoking causes many diseases including lung cancer, cardiovascular disease, and chronic obstructive pulmonary disease. However, the mechanisms of how cigarette smoke impacts disease initiation or progression are not well understood and individual smoke constituents causing these effects are not generally agreed upon. The studies reported here were part of a series of investigations into the contributions of selected smoke constituents to the biological activity of cigarette smoke. In vitro cytotoxicity measured by the neutral red uptake (NRU) assay and in vitro mutagenicity determined in the Ames bacterial mutagenicity assay (BMA) were selected because these assays are known to produce reproducible, quantitative results for cigarette smoke under standardized exposure conditions. In order to determine the contribution of individual cigarette smoke constituents, a fingerprinting method was developed to semi-quantify the mainstream smoke yields. For cytotoxicity, 90% of gas vapor phase (GVP) cytotoxicity of the Kentucky Reference cigarette 1R4F was explained by 3 aldehydes and 40% of the 1R4F particulate phase cytotoxicity by 10 smoke constituents, e.g., hydroquinone. In the microsuspension version of the BMA, 4 aldehydes accounted for approximately 70% of the GVP mutagenicity. Finally, the benefits of performing such studies along with the difficulties in interpretation in the context of smoking are discussed.

Hematological and hepatic alterations in Brazilian population heavily exposed to organochlorine pesticides

The aim of this study was to investigate the frequency of hematological and hepatic alterations and possible association with serum levels of beta-hexachlorocyclohexane (beta-HCH), p,p'-DDE, and hexachlorobenzene (HCB) among residents in an area heavily contaminated with organochlorine (OC) pesticides. A cross-sectional study was conducted in 415 male and 432 female residents aged >14 years. Serum samples were collected and analyzed for OC pesticides concentrations and biochemical parameters. Frequencies of hematological and hepatic alterations were calculated for each gender. Association between beta-HCH, p,p'-DDE (1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene), and HCB levels and presence of alterations was determined by logistic regression stratified by gender and controlling for confounders. Highest frequencies were observed for eosinophilia (23% men and 18% women), low hemoglobin (12% men and 15% women), and low erythrocyte count (12% men). High levels of bilirubin, glutamic-oxaloacetic transaminase (GOT), and glutamic-pyruvic transaminase (GPT) were observed, respectively, in 10, 11, and 12% of men and <10% of women. Gamma-glutamyl transferase (GGT) was elevated in 26 and 25% of males and females, respectively. Multivariate analysis revealed associations between eosinophilia and beta-HCH in men (OR = 1.06, 95%CI = 1.01-1.12) and women (OR = 1.05, 96%CI = 0.99-1.11), p,p'-DDE in men (OR = 1.03, 95%CI = 0.99-1.06) and women (OR = 1.02, 95%CI = 0.99-1.06), and HCB in women (OR = 1.54, 95%IC = 0.85-4.45). Beta-HCH was found to be associated with increased risk of elevated bilirubin in females (OR = 1.18, 95%CI = 1.07-1.29) and males (OR = 4.21, 95%CI = 1.87-9.47 for fourth vs. first quintile). Thus, OC pesticides may exert adverse effects on hematopoietic tissue and liver in populations chronically exposed to high levels of these compounds.

Effects of oil pollution and persistent organic pollutants (POPs) on glycerophospholipids in liver and brain of male Atlantic cod (Gadus morhua)

Fish in the North Sea are exposed to relatively high levels of halogenated compounds in addition to the pollutants released by oil production activities. In this study male Atlantic cod (Gadus morhua) were orally exposed to environmental realistic levels (low and high) of weathered crude oil and/or a mixture of POPs for 4weeks. Lipid composition in brain and in liver extracts were analysed in order to assess the effects of the various pollutants on membrane lipid composition and fatty acid profiles. Transcriptional effects in the liver were studied by microarray and quantitative real-time RT-PCR. Chemical analyses confirmed uptake of polychlorinated biphenyls (PCBs) and chlorinated pesticides, polybrominated diphenyl ethers (PBDEs) and perfluorooctanesulfonate (PFOS) in the liver and excretion of metabolites of polyaromatic hydrocarbons (PAHs) in the bile. Treatment with POPs and/or crude oil did not induce significant changes in lipid composition in cod liver. Only a few minor changes were observed in the fatty acid profile of the brain and the lipid classes in the liver. The hypothesis that pollution from oil or POPs at environmental realistic levels alters the lipid composition in marine fish was therefore not confirmed in this study. However, the transcriptional data suggest that the fish were affected by the treatment at the mRNA level. This study suggests that a combination of oil and POPs induce the CYP1a detoxification system and gives an increase in the metabolism and clearing rate of PAHs and POPs, but with no effects on membrane lipids in male Atlantic cod.

The insecticide 1,1,1-trichloro-2,2-bis(p-chlorophenyl) ethane (DDT) alters the membrane raft location of the TSH receptor stably expressed in Chinese hamster ovary cells

DDT is a highly lipophilic molecule known to deplete membrane rafts of their phosphoglycolipid and cholesterol contents. However, we have recently shown that DDT can also alter the thyroid homeostasis by inhibiting TSH receptor (TSHr) internalization. The present study was undertaken to verify whether DDT goitrogenic effects are due to the insecticide acting directly on TSHr or via alteration of the membrane rafts hosting the receptor itself. Our results demonstrate that, in CHO-TSHr transfected cells, TSHr is activated in the presence of TSH, while it is inhibited following DDT exposure. DDT can also reduce the endocytic vesicular traffic, alter the extension of multi-branched microvilli along their plasma membranes and induce TSHr shedding in vesicular forms. To verify whether TSHr displacement might depend on DDT altering the raft constitution of CHO-TSHr cell membranes the extent of TSHr and lipid raft co-localization was examined by confocal microscopy. Evidence shows that receptor/raft co-localization increased significantly upon exposure to TSH, while receptors and lipid rafts become dislodged on opposite cell poles in DDT-exposed CHO-TSHr cells. As a control, under similar culturing conditions, diphenylethylene, which is known to be a lipophilic substance that is structurally related to DDT, did not affect the extent of TSHr and lipid raft co-localization in CHO-TSHr cells treated with TSH. These findings corroborate and extend our view that, in CHO cells, the DDT disrupting action on TSHr is primarily due to the insecticide acting on membranes to deplete their raft cholesterol content, and that the resulting inhibition on TSHr internalization is due to receptor dislodgement from altered raft microdomains of the plasma membrane.

Does lipophilicity of toxic compounds determine effects on drought tolerance of the soil collembolan Folsomia candida?

The ability of Collembola to survive drought stress is crucial for their distribution in the terrestrial environment. Previous studies have suggested that several toxic compounds affect the drought tolerance of Folsomia candida in a synergistic manner and that these compounds have the feature in common that they elicit their toxicity by causing membrane damage. We hypothesised that the detrimental effect of toxic chemicals on drought tolerance in F. candida depends on the lipophilicity (log K(ow)) of the compound because a higher log K(ow) would mean a closer interaction with membranes. In this study the three chemicals 4-nonylphenol, pyrene and p,p'-DDE were tested. Surprisingly, 4-nonylphenol, with the lowest log K(ow), was the most potent with respect to reducing drought tolerance followed by pyrene, suggesting that interactions between drought tolerance and chemical stress do not depend on lipophilicity alone.

Comparative effects of herbicide dicamba and related compound on plant mitochondrial bioenergetics

The herbicide dicamba (3,6-dichloro-2-methoxybenzoic acid) was evaluated for its effects on bioenergetic activities of potato tuber mitochondria to elucidate putative mechanisms of action and to compare its toxicity with 2-chlorobenzoic acid. Dicamba (4 micro mol/mg mitochondrial protein) induces a limited stimulation of state 4 respiration of ca. 10%, and the above concentrations significantly inhibit respiration, whereas 2-chlorobenzoic acid maximally stimulates state 4 respiration (ca. 50%) at about 25 micro mol/mg mitochondrial protein. As opposed to these limited effects on state 4 respiration, transmembrane electrical potential is strongly decreased by dicamba and 2-chlorobenzoic acid. Dicamba (25 micro mol/mg mitochondrial protein) collapses, almost completely, Deltapsi; similar concentrations of 2-chlorobenzoic acid promote Deltapsi drops of about 50%. Proton permeabilization partially contributes to Deltapsi collapse since swelling in K-acetate medium is stimulated, with dicamba promoting a stronger stimulation. The Deltapsi decrease induced by dicamba is not exclusively the result of a stimulation on the proton leak through the mitochondrial inner membrane, since there was no correspondence between the Deltapsi decrease and the change on the O(2) consumption on state 4 respiration; on the contrary, for concentrations above 8 micro mol/mg mitochondrial protein a strong inhibition was observed. Both compounds inhibit the activity of respiratory complexes II and III but complex IV is not significantly affected. Complex I seems to be sensitive to these xenobiotics. In conclusion, dicamba is a stronger mitochondrial respiratory chain inhibitor and uncoupler as compared to 2-chlorobenzoic acid. Apparently, the differences in the lipophilicity are related to the different activities on mitochondrial bioenergetics.

Fenitrothion-induced structural and functional perturbations in the yolk lipoproteins of the shrimp Macrobrachium borellii

Two lipovitellin (LV) forms containing the same apoproteins but differing in their lipid composition were isolated from Macrobrachium borelii eggs at early (LVe) and late (LVI) embryogenic stages and characterized. These two forms of LV, as well as liposomes prepared with lipids extracted from them, were used as simpler models to study the effect of the pesticide fenitrothion (FS) on their structures and functions. Rotational diffusion and fluorescence lifetime of two fluorescent probes [1,6-diphenyl-1,3,5-hexatriene (DPH) and 3-(p-(6-phenyl)-1,3,5-hexatrienal)phenylpropionic acid (DPH-PA)] were used to obtain information on structural changes induced by FS in the inner and outer regions of the LV, respectively. Comparison of the rotational behavior of these probes in native LV and liposomes (LP) from extracted LV lipids suggests that apoprotein-lipid interactions result in an ordered neutral lipid core. FS increased the lipid phase polarity of both LV and LP forms. The rotation of these probes in LP was not affected, suggesting a dependence of FS action on lipid-protein interactions. DPH-PA steady-state anisotropy showed that, unlike the LVe form, the LVI form was sensitive to extremely low FS concentrations. The ability of both LV to transfer palmitic acid to albumin was increased, but in a dissimilar manner, by the presence of FS. Such differences in the sensitivity of the LV at different steps of embryogenesis to FS influence the toxic action of this insecticide.

Erythrocyte damage in mild and severe psoriasis

BACKGROUND

Psoriasis is a common chronic and recurrent inflammatory skin disorder. Oxygen metabolites and proteases released by activated inflammatory cells may induce oxidative and proteolytic damage to plasma constituents and red blood cells (RBCs). RBCs have a limited biosynthesis capacity and poor repair mechanisms.

OBJECTIVES

To study RBCs as a potential cumulative marker of oxidative and proteolytic stress in psoriasis, and as a marker of worsening of the disease.

METHODS

The study was performed in 70 patients with mild or severe psoriasis and in 40 control individuals. We evaluated total and differential leucocyte count and, as markers of leucocyte activation, plasma elastase and lactoferrin. Besides the basic RBC study (RBC count, haematocrit, haemoglobin concentration and haematimetric indices) we evaluated antioxidant defences (catalase, superoxide dismutase, glutathione peroxidase and selenium), osmotic fragility and reticulocyte count; in the RBC membrane we evaluated lipid peroxidation and susceptibility to lipid peroxidation, membrane fluidity, levels of cholesterol and phospholipids, membrane-bound haemoglobin, band 3 profile and levels of vitamin E; serum levels of bilirubin, total plasma antioxidant capacity, lipid profile and lipid peroxidation were also evaluated.

RESULTS

Psoriasis patients showed a rise in leucocytes, mainly neutrophils, which was associated with a rise in elastase and lactoferrin. Patients had a reduced RBC count, antioxidant defences and membrane fluidity, elevated membrane lipid peroxidation, membrane-bound haemoglobin, osmotic fragility and reticulocyte count, and a different band 3 profile. Most of these modifications were enhanced in severe psoriasis.

CONCLUSIONS

In summary, our data show that the RBCs are at a lower number in psoriasis patients, and present several changes denoting an enhanced damage and/or ageing process, which seem to be strongly connected with neutrophil activation, oxidative stress and worsening of psoriasis.

Fluorescent probes for bacterial cytoplasmic membrane research

Fluorescent methods in biological and medical research are extremely useful at the cellular and molecular levels. This is due to sensitive and affordable detection equipment and a variety of specific and more general fluorescent probes, and analytical procedures. In this article, I examine the use of fluorescence membrane probes to study the fluidity (membrane polarization) of the bacterial cytoplasmic membrane, central to energy transduction, ion and nutrient transport and diffusion of water and gases.

Effect of selected environmental and physico-chemical factors on bacterial cytoplasmic membranes

Membranes lipids are one of the most adaptable molecules in response to perturbations. Even subtle changes of the composition of acyl chains or head groups can alter the packing arrangements of lipids within the bilayer. This changes the balance between bilayer and nonbilayer lipids, serving to affect bilayer stability and fluidity, as well as altering lipid-protein interactions. External factors can also change membrane fluidity and lipid composition; including temperature, chemicals, ions, pressure, nutrients and the growth phase of the microbial culture. Various biophysical techniques have been used to monitor fluidity changes within the bacterial membrane. In this review, bacterial cytoplasmic membrane changes and related functional effects will be examined as well as the use of fluorescence polarization methods and examples of data obtained from research with bacteria.

Effect of fenitrothion on the physical properties of crustacean lipoproteins

The effect of the liposoluble organophosphorus insecticide fenitrothion (FS) on lipid packing and rotation of two crustacean plasma HDL was investigated. These lipoproteins, HDL-1 and HDL-2, differed in their lipid composition, but their lipid/protein ratios were similar. The rotational behavior of the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and 3-(p-(6-phenyl)-1,3,5-hexatrienyl) phenylpropionic acid (DPH-PA) was used to obtain information about the lipid dynamics in the outer and inner regions, respectively, of the lipid phase of the lipoproteins. Fluorescent steady-state anisotropy (r(s)), lifetime (tau), rotational correlation time (tau(r)), and the limiting anisotropy (r(infinity)) of these probes were measured in the lipoproteins exposed to different concentrations of FS in vitro. The results showed the penetration of FS into both plasma lipoproteins, altering the lipid dynamics of the inner as well as the outer regions. The overall effect of the insecticide was to induce an increase in the lipid order in a concentration-dependent fashion. DPH and DPH-PA fluorescence-lifetime shortening indicated that FS increased the polarity of the probe environment, suggesting an enhanced water penetration into the lipoprotein lipid phase, may be due to the induction of failures in the lipid packing. Even in the absence of FS, a higher ordering of the lipid phase was found in HDL-2 compared to HDL-1, a fact that might be attributed to a higher percentage of sphingomyelin in HDL-2.

Cypermethrin-induced plasma membrane perturbation on erythrocytes from rats: reduction of fluidity in the hydrophobic core and in glutathione peroxidase activity

The effects of treatment with the synthetic insecticide cypermethrin on plasma membrane fluidity, lipid peroxidation and antioxidant status in rat erythrocytes were investigated. Rats were treated by gavage with a low dose (12.5 mg/kg body weight per day) of cypermethrin in corn oil for 60 days. DPH and TMA-DPH fluorescence anisotropy experiments show that cypermethrin treatment, compared with controls, induced a significant decrease in erythrocyte membrane fluidity measured by DPH, while no changes were observed using TMA-DPH. Cypermethrin treatment also induced a significant increase in the lipid peroxidation, measured by the formation of conjugated dienes. The increased oxidative stress resulted in a significant decrease in the activity of glutathione peroxidase. The results are discussed in terms of preferential localization of cypermethrin in the hydrophobic core of the membrane, where it increases lipid packing and consequently decreases membrane fluidity.

Aroclor 1254 inhibits the mitochondrial permeability transition and release of cytochrome c: a possible mechanism for its in vivo toxicity

The mitochondrial permeability transition (MPT) occurs in several forms of necrotic cell death induced by various insults, including oxidative stress, ischemia/reperfusion injury Ca(2+)-ionophore toxicity, and apoptosis. In fact, the release of an apoptogenic factor such as cytochrome c is often associated with the opening of the transition pore. The present study shows that Aroclor 1254, a mixture of polychlorinated biphenyls that was banned in the U.S. in 1977 but is still present in the environment, inhibits the MPT in a dose-dependent manner in a concentration range of 1 to 25 nmol/mg protein. The compound prevents key phenomena associated with the MPT, including colloid-osmotic swelling, the collapse of membrane potential, nonspecific bidirectional traffic of solutes through the transition pore, and the oxidation of pyridine nucleotides. In contrast, Aroclor 1254 does not inhibit uptake of Ca(2+) or P(i). The effects of Aroclor 1254 are evident both in sucrose-based media and in saline and are observed when the compound is added before the opening of the pore. Aroclor 1254 prevents MPT induction provoked by a variety of agents, including phosphate, menadione, tert-butylhydroperoxide, and atractyloside. Aroclor 1254 also inhibits the specific release of cytochrome c, a correlate of MPT induction. These effects reveal a possible toxicological mechanism of action of this compound. The possibility that its effect on mitochondrial function is linked to its action as a tumor promoter is discussed.

Effect of fenitrothion on dipalmitoyl and 1-palmitoyl-2-oleoylphosphatidylcholine bilayers

The effects of the organophosphorous insecticide fenitrothion (phosphorothioic acid, O,O-dimethyl O-(3-methyl-4-nitrophenyl) ester; FS) on the physical state of pure dipalmitoyl (DPPC) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) membranes were investigated. FS lowers the phase transition temperature of DPPC. It has no large effects on the DPPC gel phase, but it increases the order of the liquid-crystalline state of DPPC and POPC. FS also decreases 1,6-diphenyl-1,3,5-hexatriene (DPH) lifetime (tau) in the DPPC and POPC liquid-crystalline states. Since a direct quenching of DPH emission by FS was ruled out, tau shortening is assigned to an increased water penetration in the bilayer. The effect of FS is different from most perturbing agents for which an increased order is accompanied by a higher tau. Furthermore, quenching of DPH by KI was increased by FS in POPC liposomes indicating an increased accessibility of the quencher to the hydrophobic core where DPH distributes. The effect of FS on dipole relaxation at the hydrophilic-hydrophobic interface of POPC bilayers was studied with 2-dimethylamino-6-lauroylnaphthalene (Laurdan). FS produces a decrease in Laurdan tau and a narrowing of its emission band. FS significantly increases the generalized polarization values at both emission band ends. These results indicate that FS may allow the coexistence of microdomains that have different physical properties.

Perturbations induced by alpha- and beta-endosulfan in lipid membranes: a DSC and fluorescence polarization study

The interaction of alpha- and beta-endosulfan isomers with lipid bilayers was searched by differential scanning calorimetry (DSC) and fluorescence polarization of 2-, 6- and 12-(9-anthroyloxy) stearic acids (2-AS, 6-AS and 12-AS) and 16-(9-anthroyloxy) palmitic acid (16-AP). Both endosulfan isomers, at insecticide/lipid molar ratios ranging from 1/40 to 1/1, shift the phase transition midpoint to lower temperature values and broaden the transition profile of dipalmitoylphosphatidylcholine (DPPC) bilayers. At insecticide/lipid molar ratios of 1/40, the isomers fully abolish the bilayer pretransition. Conversely to beta-endosulfan, alpha-endosulfan promotes a new phase transition, centered at 35.4 degrees C, in addition to the main phase transition of DPPC. Therefore, the alpha-isomer may undergo a heterogeneous distribution in separate domains in the plane of the membrane, whereas the beta-isomer may undergo a homogeneous distribution. Fluorescence polarization data indicate that alpha-endosulfan increases the lipid structural order in the regions probed by 2-AS and decreases it in the regions probed by 6-AS, 12-AS and 16-AP. On the other hand, the beta-isomer produces disordering effects in the upper regions of the bilayers, probed by 2-AS, and ordering in deeper regions, probed by 6-AS, 12-AS and 16-AP, mainly in the gel phase. The incorporation of cholesterol into DPPC bilayers progressively decreases the effects of beta-isomer which are vanished at 20 mol% cholesterol. However, this and higher cholesterol concentrations did not prevent alpha-endosulfan membrane interaction, as revealed by DSC and fluorescence polarization. The distinct effects promoted by alpha- and beta-endosulfan are discussed in terms of molecular orientation and positioning within the bilayer. Apparently, the alpha-isomer preferentially locates closer to the phospholipid headgroups whereas the beta-isomer distributes in deeper domains of the bilayer.

Effects of urea and trimethylamine N-oxide on fluidity of liposomes and membranes of an elasmobranch

The effects on membrane fluidity of two solutes of biological importance in elasmobranch fishes, urea and trimethylamine oxide (TMAO), were determined using elasmobranch red blood cell plasma membranes and artificial liposomes. Fluorescence polarizations of three probes with differing sites of insertion (1, 6-diphenylhexatriene, cis-parinaric acid, and trans-parinaric acid) were used to study the effects of physiological levels of urea (400 mM) and TMAO (200 mM) separately and together in a 2:1 urea:TMAO ratio (400 mM:200 mM). In the elasmobranch erythrocyte membrane, there was a trend toward an increase in the order of the gel-phase domains when treated with urea, although this was not statistically significant. This effect was counteracted by the presence of TMAO. To determine if the organic solutes were acting directly on the membrane lipids or on the integral proteins, phase-transition profiles of protein-free dipalmitoyl phosphatidylcholine liposomes were determined. These profiles showed that urea again increased the order of the gel-phase domains of the bilayer; however, this effect was not counteracted by the presence of TMAO. We suggest that the increased order in the gel-phase domains may be an indirect effect of a decrease in the order of the fluid-phase domains. This increase in fluidity may be due either to a disruptive effect of urea on the hydrophobic core of the membrane or to indirect effects mediated by changes in the integral membrane proteins. This study is the first to demonstrate that urea and TMAO may act as counteracting solutes in the elasmobranch erythrocyte membrane and that the counteraction appears to be at the level of the integral proteins rather than the membrane lipids.

Biophysical perturbations induced by ethylazinphos in lipid membranes

Perturbations induced by ethylazinphos on the physical organization of dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol membranes were studied by differential scanning calorimetry (DSC) and fluorescence polarization of 2-, 6-, 12-(9-anthroyloxy) stearic acids and 16-(9-anthroyloxy) palmitic acid. Ethylazinphos (50 and 100 microM) increases the fluorescence polarization of the probes, either in the gel or in the fluid phase of DPPC bilayers, and this concentration dependent effect decreases from the surface to the bilayer core. Additionally, the insecticide displaces the phase transition to a lower temperature range and broadens the transition profile of DPPC. A shifting and broadening of the phase transition is also observed by DSC. Furthermore at insecticide/lipid molar ratios higher than 1/7, DSC thermograms, in addition to the normal transition centered at 41 degrees C, also display a new phase transition centered at 45.5 degrees C. The enthalpy of this new transition increases with insecticide concentration, with a corresponding decrease of the main transition enthalpy. Ethylazinphos in DPPC bilayers with low cholesterol (< or = 20 mol%) perturbs the membrane organization as described above for pure DPPC. However, cholesterol concentrations higher than 20 mol% prevent insecticide interaction, as revealed by fluorescence polarization and DSC data. Apparently, cholesterol significantly modulates insecticide interaction by competition for similar distribution domains in the membrane. The present results strongly support our previous hypothesis that ethylazinphos locates in the cooperativity region, i.e. the region of C1-C9 atoms of the acyl chains, and extends to the lipid-water interface, where it increases lipid packing order sensed across all the thickness of the bilayer. Additionally, and, on the basis of DSC data, a lateral regionalization of ethylazinphos is here tentatively suggested.

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

Comparative study of the toxic actions of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane and 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene on the growth and respiratory activity of a microorganism used as a model

A strain of Bacillus stearothermophilus was used as a model for a comparative study of the toxic effect of 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane and 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene. Bacterial growth, the O2 consumption rate, and respiration-related enzymatic activities provided quantitative data in agreement with results reported for other systems. The use of this bacterium for screening for chemical toxicity is discussed.

G-proteins and beta-adrenergic stimulation of adenylate cyclase activity in the diabetic rat prostate

BACKGROUND

The consequences of experimental diabetes on membrane lipids, beta-adrenergic stimulation of adenylate cyclase activity, and G-protein levels in the prostate gland are not defined.

METHODS

Prostatic membranes from control and streptozotocin (STZ)-diabetic rats were used to study adenylate cyclase stimulation as well as for immunodetection of stimulatory (alpha s) and inhibitory (alpha i) G-protein subunits. Changes in membrane lipid composition were estimated by [1-14C] acetate incorporation into lipid subclasses.

RESULTS

The efficacy of isoproterenol on stimulation of adenylate cyclase activity and the levels of alpha s, alpha i1/2, and alpha i3/0 G-protein subunits were drastically reduced in prostatic membranes from STZ-diabetic rats. Insulin treatment of diabetic rats tended to normalize G-protein levels, but it was ineffective on the poor adenylate cyclase response to isoproterenol or forskolin. However, it prevented enzyme desensitization to vasoactive intestinal peptide. The pattern of [1-14C] acetate incorporation into lipid subclasses did not vary with diabetes or insulin treatment.

CONCLUSIONS

STZ-induced diabetes results in desensitization for the beta-adrenergic response of adenylate cyclase, as supported by previous data on the low density of beta-adrenergic receptors and the present results on the general decrease of Gs and Gi proteins levels and even of the enzyme itself in the diabetic rat prostate.

Interaction of ethylazinphos with the physical organization of model and native membranes

The interaction of ethylazinphos with the physical organization of model and native membranes was investigated by means of fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and of its propionic acid derivative (DPH-PA). Ethylazinphos shifts the phase transition midpoint to lower temperature values and broadens the phase transition profile of bilayers reconstituted with dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholines (DMPC, DPPC, DSPC), as detected by DPH and DPH-PA. Additionally, both probes detect significant effects of ethylazinphos in the fluid phase of the above lipid bilayers. The insecticide perturbations are more pronounced in bilayers of short-chain lipids, e.g., DMPC, in correlation with the higher partition in these membranes. On the other hand, the insecticide increases to some extent the ordering promoted by cholesterol in the fluid phase of DMPC, but high cholesterol concentrations (> or = 30 mol%) almost prevent insecticide interaction, as revealed by DPH and DPH-PA. In agreement with the results in models of synthetic lipids, the increase of intrinsic cholesterol in fluid native membranes depresses the partition values of ethylazinphos and consequently its effects.

Correlation of the lipophilicity of xenobiotics with their synergistic effects on DNA synthesis in human fibroblasts

The binary combination effects of DNA synthesis of human fibroblasts were investigated using 2,4-D with 15 xenobiotics of different chemical substance classes. Results were compared with previous investigations on cell growth. Each of the 15 chemicals tested at their no effect concentrations (NOEC's) increased the effects of 2,4-D on DNA synthesis. Thereby, the EC20 value of 2,4-D was reduced by approximately 40% in the combinations. The NOEC's of the xenobiotics used in the combinations varied by a factor of 1,600 and depended strongly on the lipophilicity of the agents combined with 2,4-D. A significant statistical correlation of r = 0.90 was found between the NOEC's of the 15 combined xenobiotics and their lipophilicity. The combination effects on DNA synthesis were similar to those on cell growth. The regression lines of the relationship between the NOEC's and lipophilicity in both assays showed only slight differences in the slopes. This is an additional confirmation of our hypothesis on a facilitated uptake of 2,4-D in the binary combinations.

Effects of the pyrethroid insecticide permethrin on membrane fluidity

The interaction of permethrin with dimyristoyl- (DMPC), dipalmitoyl- (DPPC) and distearoyl- (DSPC) bilayers has been investigated by differential scanning calorimetry (DSC) and DPH and TMA-DPH fluorescence anisotropy. In experiments performed by DSC, we show that the addition of permethrin to liposomes, in a 5:1 phospholipid/pyrethroid ratio, decreases the phase transition temperature (Tm) of DMPC, DPPC and DSPC by 3.2, 2.3 and 1.1 degrees C, respectively. Furthermore, DSC profiles reveal that permethrin decreases the cooperativity for the phase transition of DMPC, DPPC and DSPC membranes. DPH and TMA-DPH fluorescence anisotropy experiments show that permethrin increases membrane fluidity at temperatures below the Tm. The results are discussed in terms of a preferential localization of permethrin in the hydrophobic core of the membrane, where it diminishes the lipid packing in the gel phase and has no effect in the liquid-crystalline phase.

Correlation of synergistic cytotoxic effects of environmental chemicals in human fibroblasts with their lipophilicity

The cytotoxic combination effects of 2,4-D with 12 xenobiotics having different lipophilicity were investigated in human fibroblasts at their no effect concentrations (NOEC). Each of the chemicals tested in binary combinations enhanced the toxicity of 2,4-D. These synergistic combination effects were independent of the chemical structure of the test compounds. However, the NOEC's of the xenobiotics used in the combinations varied by a factor of 10,000. For strongly lipophilic compounds the lowest NOEC's were needed to induce synergistic cytotoxicity. A linear regression analysis of the concentrations (NOEC's) of the 12 combined xenobiotics against their lipophilicity revealed a correlation with r = 0.96 for 11 agents. This close correlation may be explained by the membrane damaging properties of lipophilic compounds which enhance the uptake of hydrophilic agents.

Mechanism of citrinin-induced dysfunction of mitochondria. III. Effects on renal cortical and liver mitochondrial swelling

The effects of the mycotoxin citrinin on renal cortical and liver mitochondrial swelling were studied. Citrinin decreases the rate of swelling induced by the valinomycin-K+ complex, suggesting that the mycotoxin interferes with the mitochondrial membrane fluidity. Citrinin promotes reduction of the amplitude of swelling in the presence of Na+ ions. This alteration reflects interference with complex I of the respiratory chain and ATP synthase complex activity without disarranging the inner mitochondrial membrane, in view of the fact that the shrinkage was not affected. The effect increases with citrinin concentration. Renal tissue is more susceptible than hepatic tissue.

Calorimetric and theoretical studies of the effects of lindane on lipid bilayers of different acyl chain length

The effects of the insecticide lindane on the phase transition in multilamellar bilayers of saturated diacylphosphatidylcholines of different acyl chain length (DC14PC, DC16PC, and DC18PC) have been studied by means of differential scanning calorimetry (DSC), as well as computer-simulation calculations on a molecular interaction model. The calorimetric data show that increasing concentrations of lindane lower the transition temperature and lead to a broadening of the specific heat in a systematic way depending on the lipid acyl chain length. Kinetic effects in the observed calorimetric traces indicate that the incorporation of lindane into multilamellar lipid bilayers is slow, but faster for the shorter lipid species. Large unilamellar vesicles do not show such kinetic effects. The transition enthalpy is for all three lipid species found to be independent of the lindane concentration which implies that the entropy of mixing is vanishingly small. This lends support to a microscopic molecular interaction model which assigns the absorbed lindane molecules to interstitial sites in the bilayer. Computer-simulation calculations on this model, which assumes a specific interaction between lindane and certain excited acyl chain configurations, lead to predictions of the lipid-water partition coefficient in qualitative agreement with experimental measurements (Antunes-Madeira and Madeira (1985) Biochim. Biophys. Acta 820, 165-172). The partition coefficient has a peak near the phase transition which is a consequence of enhanced interfacial adsorption of lindane at lipid-domain interfaces.

Role of lindane in membranes. Effects on membrane fluidity and activity of membrane-bound proteins

The influence of lindane (gamma-hexachlorocyclohexane) on fluidity of plasma membranes from rat renal cortical tubules has been investigated. Preincubation with lindane increased membrane fluidity. This effect was accompanied by (i) a decrease in the transport of glucose with regard to the controls and (ii) an inhibition of the beta-adrenergic stimulatory activity upon cyclic AMP accumulation. However, a significant decrease of the membrane fluidity was found when rats were injected with lindane for 12 days. The injection of lindane exerted the opposite effect on the membrane proteins, the glucose transporter and the beta-adrenergic receptor, enhancing the glucose uptake and increasing the isoproterenol-stimulated cycle AMP accumulation. A possible explanation of the difference could involve a resistance to membrane disordering by lindane through a regulatory mechanism that would balance the activity of many lindane-sensitive proteins in insecticide-injected rats.

Effects of parathion on membrane organization and its implications for the mechanisms of toxicity

The effects of the organophosphorus insecticide parathion (O,O-diethyl O-(p-nitrophenyl)phosphorothioate) on the physical state of synthetic and native membranes was investigated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and by its anionic propionic acid derivative (DPH-PA), probing the outer regions of the bilayer. Parathion disorders the gel phase of liposomes reconstituted with dimyristoylphosphatidylcholine (DMPC), broadening the transition profile and shifting the temperature midpoint of the phase transition, as detected by both probes. The insecticide strongly orders the fluid phase either in the hydrophobic core or in the outer regions of the membrane, as evaluated by DPH and DPH-PA, respectively. These ordering effects of parathion were further confirmed in fluid models of egg-yolk phosphatidylcholine. Parathion increases to some extent the ordering promoted by cholesterol in DMPC bilayers, but high cholesterol concentrations (> or = 30 mol%) prevent parathion interaction. The results in native membranes correlate reasonably with those obtained in models of synthetic lipids. Thus, parathion does not exert detectable effects in cholesterol-rich membranes, namely, erythrocytes, but moderate ordering effects of parathion are detected by both probes in brain microsomes, i.e., membranes with a lower content of cholesterol. Again, in agreement with the models of synthetic lipids, pronounced ordering effects of parathion are detected in cholesterol-poor membranes, e.g., sarcoplasmic reticulum and mitochondria.

The active metabolite hydroxytamoxifen of the anticancer drug tamoxifen induces structural changes in membranes

The effects of hydroxytamoxifen (OHTAM) on lipid organization of pure phospholipid liposomes, native sarcoplasmic reticulum (SR) membranes and liposomes of SR lipids were evaluated by intramolecular excimer formation of 1,3-di(1-pyrenyl)propane (Py(3)Py) and by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and its derivative 3-[p-(6-phenyl)-1,3,5-hexatrienyl]phenylpropionic acid (DPH-PA). OHTAM promotes alterations in the thermotropic profiles of DMPC, DPPC and DSPC. As detected by Py(3)Py and DPH-PA, OHTAM induces an ordering effect in the fluid phase and a fluidizing effect in the temperature range of the cooperative phase transition. In the gel phase, no significant effects are noticed, except for DSPC bilayers, where Py(3)Py and DPH-PA detect a disordering effect. In the hydrophobic region of the above membrane systems probed by DPH, OHTAM induces only a slight fluidizing effect in the range of the phase transition and a small ordering effect in the fluid phase. As detected by all probes, the drug broadens the transition profile of DMPC and shifts the main transition temperature to lower values. However, these effects, and so those observed for the fluid phase, decrease as the fatty acyl chain length increases. Moreover, the drug removes the pre-transitions of DPPC and DSPC bilayers, as probed by Py(3)Py. In fluid SR native membranes and liposomes of SR lipids, OHTAM induces a moderate ordering effect in the outer regions of the lipid bilayer, as monitored by Py(3)Py and by DPH-PA, DPH failing to detect any apparent effect, as observed for the fluid phase of pure phospholipids. Apparently, OHTAM distributes preferentially in the outer region of the lipid bilayer, without significant effect in the bulk lipid organization of the bilayer interior. The changes of OHTAM in the bilayer dynamic properties and the different location across the bilayer thickness relative to its drug promoter (Custódio et al. (1993) Biochim. Biophys. Acta 1150, 123-129) may be involved in the cytostatic activity of tamoxifen.

Defence mechanisms against free radical-induced damage in sheep, cattle and dog erythrocytes

1. Erythrocytes from sheep were to be found the least resistant to peroxidative stress induced in vitro as compared to those from cattle and dogs. 2. The differences found among species in alpha-tocopherol content and glutathione peroxidase activity were probably insufficient to explain the lowest resistance. 3. One of the main reasons of the lowest resistance may be found in the membrane composition and characteristics (membrane fluidity).

The anticancer drug tamoxifen induces changes in the physical properties of model and native membranes

The interactions of tamoxifen with lipid bilayers of model and native membranes were investigated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and by intramolecular excimer formation of 1,3-di(1-pyrenyl)propane (Py(3)Py). The effects of TAM of liposomes of DMPC, DPPC and DSPC are temperature dependent. In the fluid phase, TAM reduces dynamics of the upper bilayer region as observed by Py(3)Py and has no effect on the hydrophobic region as detected by DPH. In the gel phase, the effects of TAM evaluated by Py(3)Py are not discernible for DMPC and DPPC bilayers, whereas DSPC bilayers become more fluid. However, DPH detects a strong fluidizing effect of TAM in the hydrophobic region of the above membrane systems, where DPH distributes, as compared with the small effects detected by Py(3)Py. TAM decreases the main phase transition temperature but does not extensively broaden the transition thermotropic profile of pure lipids, except for bilayers of DMPC where TAM induces a significant broadening detected with the two probes. In fluid liposomes of sarcoplasmic reticulum lipids and native membranes, TAM induces an ordering effect, as evidenced by Py(3)Py, failing DPH to detect any apparent effect as observed for the fluid phase of liposomes of pure lipid bilayers. These findings confirm the hydrophobic nature of tamoxifen and suggest that the localization and effects of TAM are modulated by the order and fluidity of the bilayer. These changes in the dynamic properties of lipids and the non-specific interactions with membrane lipids, depending on the order or fluidity of the biomembrane, may be important for the multiple cellular effects and action mechanisms of tamoxifen.

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 model and native membranes was studied by means of fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and by intramolecular excimerization of 1,3-di(1-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 regions of the membrane, as evaluated by DPH and Py(3)Py, respectively. Regarding the fluid phase, DDE has no apparent effect on the bilayer center, but it induces a limited ordering effect on the outer regions. Similar effects are described for bilayers of DPPC and DSPC. Unlike DPH, Py(3)Py is very sensitive to DPPC and DSPC pretransitions, not abolished by DDE (50 microM), as opposite to the effects observed with lindane (Antunes-Madeira, M.C., Almeida, L.M. and Madeira, V.M.C. (1990) Biochim. 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 (> or = 30 mol%) do not prevent DDE interaction, as evaluated by DPH. On the other hand, the effects of DDE reported by Py(3)Py depend on temperature and cholesterol contents of DMPC bilayers. For cholesterol levels ranging from 10 to 50 mol% and temperatures below the phase transition of DMPC, Py(3)Py fails to detect any significant 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 (> or = 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 membranes of sarcoplasmic reticulum, but detects moderate disordering effects in membranes of brain microsomes and erythrocytes, i.e., membranes with high cholesterol. On the other hand, Py(3)Py reports ordering effects of DDE in fluid membranes of sarcoplasmic reticulum, an effect similar to that observed in fluid systems of synthetic lipids without or with low cholesterol. Additionally, as described for models, Py(3)Py detects disordering effects of DDE in cholesterol rich membranes, namely, brain microsomes.

Effect of fenvalerate, a pyrethroid insecticide on membrane fluidity

Fenvalerate is a commonly used pyrethroid insecticide, used to control a wide range of pests. We have studied its interaction with the membrane using fluorescence polarization and differential scanning calorimetry (DSC) techniques. Fenvalerate was found to decrease the DPH fluorescence polarization value of synaptosomal and microsomal membrane, implicating that it makes the membrane more fluid. At different concentrations of fenvalerate, the activation energy of the probe molecule in the membrane also changes revealed from the change in slope of the Arrhenius plot. At higher concentrations the insecticide slowly saturates the membrane. The effects of fenvalerate on model membrane were also studied with liposomes reconstituted with dipalmitoylphosphatidylcholine (DPPC). Fenvalerate decreased the phase transition temperature (Tm) of DPPC by 1.5 C degrees at 40 microM concentration, but there was no effect on the cooperativity of the transition as interpreted from the DSC thermogram. From the change in the thermogram profile with fenvalerate it has been interpreted that it localizes in the acyl chain region of the lipid, possibly between C10 and C16 region and weakens the acyl chain packing. Fenvalerate was also found to interact with DPPC liposomes containing cholesterol to fluidize it.

Differential effect of arachidonic acid on the vasoactive intestinal peptide receptor/effector system in rat prostatic epithelium during sexual maturation

The effects of alterations in the membrane lipid environment on vasoactive intestinal peptide (VIP) binding and VIP-stimulated cyclic AMP accumulation have been analyzed by arachidonic acid treatment of prostatic epithelial cells from rats at puberty and maturity, two critical developmental periods with characteristic lipidic and androgenic statuses. Treating cells with 0.1 mM arachidonic acid for 15 min at 37 degrees C increased the affinity of VIP receptors and the potency of the neuropeptide (up to five times) in the formation of cyclic AMP at maturity, but not at puberty. The average plasma membrane fluidity (as measured by fluorescence polarization of diphenylhexatriene) remained unmodified after arachidonic acid treatment of cells. The modifications observed in mature rats were specific for the VIP receptor/effector system, since cyclic AMP stimulation by isoproterenol or forskolin was not affected by cell treatment with arachidonic acid. These results are compatible with the existence of a particular lipidic microdomain surrounding the VIP receptor in the cell membrane that would be altered by exposure to arachidonic acid (either directly or through conversion of arachidonic acid to its metabolites, as suggested by experiments on inhibition of the arachidonic acid cascade). This would make it possible for the activation of protein kinase C to phosphorylate VIP receptors in cells from mature rats, but not in those from pubertal animals with a very different membrane lipid composition (as suggested by the corresponding values of membrane fluidity and transition temperature).

Kinetic changes of ethanolamine base exchange activity and increase of viscosity in sarcolemmal membranes of hamster heart during development of cardiomyopathy

The activity of the phospholipid base exchange enzyme specific for ethanolamine has been measured in cardiac sarcolemmal membrane preparations from Syrian golden and UM-X7.1 cardiomyopathic hamsters. In Syrian golden hamsters, the Km of the enzyme for ethanolamine does not change with age, whereas it almost doubles in membranes from cardiomyopathic animals, from the 30th to the 150th day of age. During the same period, the membrane cholesterol content increases by 68% in cardiomyopathic hamsters, whereas it does not change significantly in the Syrian golden hamster strain. As a consequence, in the adult animal, the cholesterol to phospholipid ratio and the viscosity of sarcolemmal membranes are higher in UM-X7.1 strain than in Syrian golden hamsters. A cause-consequence relationship between the enzymatic changes and the compositional modifications in the sarcolemma occurring in UM-X7.1 hamsters during the development of cardiomyopathy is proposed.

Lindane-induced modifications to membrane lipid structure: effect on membrane fluidity after subchronic treatment

Chronic lindane intoxication by injecting subcutaneously the toxicant, resulted in an altered lipid pattern in rat ventral prostate membranes. An increase of membrane fluidity was also observed using a fluorescence polarization technique. When in vitro experiments were carried out with both treated and untreated rats, an interesting lack of parallelism was found, which could indicate the development of a resistance to membrane disordering by lindane. The observed changes in cholesterol and phospholipid composition are also consistent with the hypothesis that lindane perturbs the lipid matrix of membranes, possibly inducing complex compensatory changes in the membrane lipid composition.

Mitochondrial bioenergetics as affected by DDT

The organochloride insecticide DDT (2,2-bis(p-chlorophenyl)-1,1-trichloroethane) depresses the phosphorylation efficiency of mitochondria as inferred from the decrease of respiratory control ratio (RCR) and P/O ratio, perturbations of transmembrane potential (delta psi) fluctuations associated with mitochondrial energization and phosphorylative cycle induced by ADP. DDT depresses the delta psi developed by energized mitochondria and prevents complete repolarization, that is delayed and resumed at a lower rate. The inhibitory action of DDT on phosphorylation efficiency may result from: (1) a direct effect on the ubiquinol-cytochrome c segment of the redox chain; (2) direct action on the ATP-synthetase complex; (3) partial inhibition of the phosphate transporter. DDT preferentially interacts with phosphorylation process in relation to respiration. High concentrations of DDT induce destruction of the structural integrity of mitochondria.

Effects of lindane on fluidity and lipid composition in rat renal cortex membranes

The influence of lindane upon dynamic properties of plasma membranes from rat renal cortex has been investigated using a fluorescence polarization technique. Preincubation with lindane increased membrane fluidity in a manner that is dose-dependent. This increase was higher in brush border membranes than in basolateral membranes. However, a significant decrease of the membrane fluidity was found in brush border membranes when rats were injected with lindane for 12 days. A possible solution to this difference could involve a resistance to membrane disordering by lindane through a regulatory mechanism that would balance the amount of cholesterol and phospholipid classes in the renal cortex membranes of lindane-injected rats.