Membrane fluidity as affected by the insecticide lindane

Phase Transitions and Structural Changes in DPPC Liposomes Induced by a 1-Carba-Alpha-Tocopherol Analogue

Steady-state emission spectroscopy of 1-anilino-8- naphthalene sulfonate (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH), fluorescence anisotropy, and DSC methods were used to characterize the interactions of the newly synthesized 1-carba-alpha-tocopherol (CT) with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane. The DSC results showed significant perturbations in the DPPC structure for CT concentrations as low as 2 mol%. The main phase transition peak was broadened and shifted to lower temperatures in a concentration-dependent manner, and pretransition was abolished. Increasing CT concentrations induced the formation of new phases in the DPPC structure, leading to melting at lower temperatures and, finally, disruption of the ordered DPPC structure. Hydration and structural changes of the DPPC liposomes using ANS and DPH fluorescent probes, which are selectively located at different places in the bilayer, were studied. With the increased concentration of CT molecules in the DPPC liposomes, structural changes with the simultaneous formation of different phases of such mixture were observed. Temperature studies of such mixtures revealed a decrease in the temperature of the main phase transition and fluidization at decreasing temperatures related to increasing hydration in the bilayer. Contour plots obtained from concentration–temperature data with fluorescent probes allowed for identification of different phases, such as gel, ordered liquid, disordered liquid, and liquid crystalline phases. The CT molecule with a modified chromanol ring embedded in the bilayer led to H-bonding interactions, expelling water molecules from the interphase, thus introducing disorder and structural changes to the highly ordered gel phase.

Characterizing Escherichia coli's transcriptional response to different styrene exposure modes reveals novel toxicity and tolerance insights

The global transcriptional response of Escherichia coli to styrene and potential influence of exposure source was determined by performing RNA sequencing (RNA-seq) analysis on both styrene-producing and styrene-exposed cells. In both cases, styrene exposure appears to cause both cell envelope and DNA damage, to which cells respond by down-regulating key genes/pathways involved in DNA replication, protein production, and cell wall biogenesis. Among the most significantly up-regulated genes were those involved with phage shock protein response (e.g. pspABCDE/G), general stress regulators (e.g. marA, rpoH), and membrane-altering genes (notably, bhsA, ompR, ldtC), whereas efflux transporters were, surprisingly, unaffected. Subsequent studies with styrene addition demonstrate how strains lacking ompR [involved in controlling outer membrane (OM) composition/osmoregulation] or any of tolQ, tolA, or tolR (involved in OM constriction) each displayed over 40% reduced growth relative to wild-type. Conversely, despite reducing basal fitness, overexpression of plsX (involved in phospholipid biosynthesis) led to 70% greater growth when styrene exposed. These collective differences point to the likely importance of OM properties in controlling native styrene tolerance. Overall, the collective behaviours suggest that, regardless of source, prolonged exposure to inhibitory styrene levels causes cells to shift from'growth mode' to 'survival mode', redistributing cellular resources to fuel native tolerance mechanisms.

Evaluation of toxicological responses and promising biomarkers of topmouth gudgeon (Pseudorasbora parva) exposed to fipronil at environmentally relevant levels

Fipronil is an insecticide commonly used in agriculture. We report here on the sublethal and sub-chronic effects of fipronil on non-target topmouth gudgeon (Pseudorasbora parva) at environmentally relevant levels. The results showed that fipronil did not cause significant changes in brain acetylcholinesterase activities, glutathione S-transferase (GST) activities in the intestine, and GST, glutamic pyruvic transaminase (GPT), and glutamic oxaloacetic transaminase (GOT) activities in the liver tissues at environmentally relevant levels for 96-h exposure. In the further test for a 12-day exposure, dose-dependent responses of the serum GPT and GOT activities were observed in all treated groups with sublethal concentrations of fipronil. Furthermore, fipronil could reduce the liver mitochondrial membrane fluidity of P. parva, especially with high concentration of fipronil at high temperature. The results suggest that serum GPT and GOT in P. parva might be useful biomarkers for effects of fipronil exposure at environmentally relevant level, and reducing fluidity of liver mitochondrial membrane may be one toxic mechanism of fipronil.

The transport of DDT from chylomicrons to adipocytes does not mimic triacylglycerol transport

Despite being banned in the U.S., organochlorine toxins such as DDT are frequently detected in human adipose tissue. The main route of exposure is through the consumption of contaminated foods and subsequent intestinal packaging of DDT into chylomicrons. These chylomicrons, which also contain dietary triacylglycerol (TG), are delivered directly to peripheral tissues without first being metabolized by the liver. The physiological process by which these compounds are delivered from chylomicrons to adipose is not well understood, but is clinically relevant since it bypasses first-pass metabolism. Based on its highly lipophilic nature, it has been assumed that DDT is transferred to peripheral tissues similar to TG; however, this has not been measured. Here, we use the lymph fistula rat to isolate chylomicrons containing both DDT and TG. These chylomicrons are the in vivo DDT delivery vehicle. Using 3T3-L1 adipocytes, we investigated the rate at which DDT transfers from chylomicrons to adipocytes, and mediators of this process. This novel approach closely approximates the in vivo DDT exposure route. We show that: 1) DDT repartitions from chylomicrons to adipocytes, 2) this transport does not require hydrolysis of TG within the chylomicron, and is stimulated by the inhibition of LPL, 3) albumin does not inhibit DDT uptake, 4) DDT dissolved in DMSO does not appropriately mimic in vivo DDT transport; and most importantly, 5) DDT uptake from chylomicrons does not mimic the uptake of TG from the same particles. Understanding these factors is important for designing interventions for human populations exposed to DDT.

Propidium iodide staining method for testing the cytotoxicity of 2,4,6-trichlorophenol and perfluorooctane sulfonate at low concentrations with Vero cells

In this article, the feasibility of propidium iodide (PI) staining based on cell membrane damage as a sensitive and quantitative method to test the cytotoxicity of typical lipophilic compounds including 2,4,6-trichlorophenol (TCP) and perfluorooctane sulfonate (PFOS) was examined. The sensitivity of PI staining was compared to that of the methylthiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT) assay. We found a good correlation between PI uptake and increasing concentrations of TCP (10-50 μM) and PFOS (20-50 μM) at lower concentrations than those between growth inhibition ratio determined by the MTT assay and increasing concentrations of TCP (150-400 μM) and PFOS (100-500 μM). These findings indicated that the PI staining was more sensitive than the MTT assay. Furthermore, both the amount of PI uptake and the ratio of morphologically changed cells increased with increasing TCP concentrations, suggesting that PI staining may be a suitable quantitative substitute for the original method based on the observation of morphological changes in Vero cells. Our data also suggest that it is possible that the cell membrane damage that resulted in increased PI uptake may be due to variations in the phospholipid and protein content of the membrane, which are affected by interactions between the lipophilic compounds and components of the cell membrane.

Screening membrane interactions of pesticides by cells decorated with chromatic polymer nanopatches

Elucidating the factors contributing to the cell toxicity of pesticides and other environmentally sensitive small molecules is critical for evaluation of their health impacts and for understanding the biological processes that they affect. Disruption and permeation of the plasma membrane, which constitutes the critical interface between the cell and its environment, are recognized initiators of cytotoxicity. We present a new approach for predicting pesticide cytotoxicity through rapid screening of membrane interactions of pesticides using a recently developed live-cell chromatic sensor. The sensing platform comprises living mammalian cells labeled with polydiacetylene (PDA), a chromatic polymer that undergoes intense fluorescence transformations induced by structural perturbations of the membrane bilayer. Within a short time after the addition of membrane-interacting tested compounds to the labeled cells, the PDA patches emit high fluorescence, which can be monitored by conventional spectroscopy and microscopy apparatuses. The chromatic technology facilitates rapid evaluation of membrane activity of pesticide compounds and is capable of distinguishing between toxic effects associated with membrane interactions vs intracellular mechanisms.

Biomarker responses in European eel (Anguilla anguilla) exposed to persistent organic pollutants. A field study in the Vaccarès lagoon (Camargue, France)

A screening of relevant biomarkers was carried out in order to evaluate metabolic and cellular damages in European eels exposed to a non-point source contamination by persistent organic pollutants (POP) such as polycyclic aromatic hydrocarbons (PAH) and organochlorine compounds (OC) in a protected area, the Nature Reserve of Camargue (France). Investigations were focused on metabolic responses including detoxification mechanisms (biotransformation, antioxidant process), energy requirements and enzymatic membrane markers either involved in neuronal conduction (acetylcholinesterase, AChE) or in osmoregulation and energy metabolism (ATPases). The hepatic and muscular glycogen rates seemed to be suitable biomarkers as well as three hepatic activities involved in the protection against oxyradicals: catalase, glutathione peroxidase (SeGPx) and superoxide dismutases (SOD). The muscle and gill ATPases as well as the muscle and brain AChE showed more significant relevance in terms of biomarkers than the biotransformation enzymes: ethoxyresorufine-O-deethylase (EROD) and uridine diphospho-glucuronyl transferase (UDPGT). However, most of these enzymatic activities depend on numerous abiotic factors, which must be taken into account in such a biomarker assessment approach. Our study provides some conclusive elements to approve the use in situ of biomarkers developed from laboratory studies. It also raises a question regarding the location of contaminant impregnation in fish organ, in relation with age, development status or mode of contamination, and its influence on biomarker response. If the relevance of membrane indicators is confirmed, this study provides an original statement of the extent of the ecotoxicological threat for the aquatic species in a protected area, due to the occurrence of POP in the cell membranes.

Fluorescent methods to study DNA, RNA, proteins and cytoplasmic membrane polarization in the pentachlorophenol-mineralizing bacterium Sphingomonas sp. UG30 during nutrient starvation in water

The effect of sodium pentachlorophenolate (NaPCP) exposure on the nutrient-starved pentachlorophenol (PCP)-mineralizing bacterium Sphingomonas sp. UG30 was assessed using fluorescent methods to measure DNA, RNA, total cellular protein, and cytoplasmic membrane proteins. UG30 cells were inoculated into sterilized Speed River (Guelph, ON, Canada) water samples in the presence of 50, 100, and 250 ppm NaPCP. No marked changes were observed in the total cellular DNA, RNA or protein levels over 90 d, indicating the macromolecular composition of UG30 was not affected by both nutrient limitation and NaPCP. Total cell counts as determined by DAPI staining also did not change over 90 d. Over the same period, viable counts decreased with increasing concentrations of NaPCP. At 250 ppm NaPCP, viable cell counts decreased over 6 orders of magnitude after 1 hr exposure. Cell numbers partially recovered once NaPCP was degraded. The UG30 cytoplasmic membrane polarization ratio also decreased after NaPCP was depleted. The decreased polarization value at the end of the study period suggested the UG30 membrane was more fluid and that this increase in fluidity was due to nutrient starvation effects rather than exposure to NaPCP. These results indicated that UG30 is a robust organism that is able to degrade NaPCP even under adverse conditions and fluorescent methods are useful for determining macromolecular concentrations and cytoplasmic membrane polarization values.

Electrical activity alterations induced by chronic absorption of lindane (γ-hexachlorocyclohexane) trace concentrations in adult rat heart

The heart of adult rat offspring, born to mothers treated with trace concentrations of lindane (0.5 to 2 ppb) through a beverage and to mothers chronically treated with lindane (CL-T) with the same trace concentration, also through a beverage, during lactation and growth has a round shape and accumulates lindane. The left ventricle (LV) presents a hypertrophied area, atrophied papillary muscles, and unorganized collagen bundles and layers. These observations led us to study the electrical activity of their left ventricle papillary muscles (LVPM) by recording action potential using intracellular microelectrodes. CL-T shortened LVPM action potential duration (APD): 1 ppb shortened the plateau; 2 ppb shortened the plateau and the slow repolarizing phase. In CL-T (2 ppb) and untreated groups, low temperature (22 °C) decreased the resting potential and prolonged APD. TEA (tetraethylammonium; 1-2 mmol/L) partially lengthened CL-T (2 ppb lindane) APD. Quinidine (0.2 mmol/L) and E-4031 (10 nmol/L) prolonged CL-T APD, suggesting that the rapid delayed outward K+ current (IKr) was increased. Our results indicate the silent effects of chronic exposure to trace concentrations of lindane on the morphological and electrical activity of heart muscle. They demonstrate that chronic lindane treatment of female rats alters the tissue integrity and electrical activity in the LV of their offspring.Key words: heart muscle, membrane potential, lindane, K+ channel.

Lindane stimulates neutrophils by selectively activating phospholipase C and phosphoinositide-kinase activity

The organochlorine insecticide lindane is a known activator of neutrophil responses. In this work we delineated the biochemical pathways by which lindane stimulates neutrophil oxidant production. Plasma membrane GTPase activity was not stimulated by lindane, ruling out a role for lindane-induced activation of G-proteins or G-protein coupled receptors, whereas inhibition of phospholipase C inhibited lindane-induced oxidant production. Together these data pointed to phospholipase C as the direct target of lindane activation. Type I phosphoinositide 3-kinase was not significantly activated by lindane and an inhibitor of phosphoinositide 3-kinases inhibited oxidant production by only 40%. Thus, Type I phosphoinositide 3-kinase played a minor role, if any, in lindane-induced oxidant production. Lindane stimulated an increase in phosphatidylinositol phosphate suggesting a Type II or III phosphotidylinositol 3-kinase or phosphatidylinositol 4-kinase activity was also stimulated.

Effects of deltamethrin on functions of rat liver mitochondria and on native and synthetic model membranes

Deltamethrin (DTM) is a synthetic pyrethroid insecticide used wideworld in agriculture, home pest control, protection of foodstuff, and disease vector control. It has widespread applications in Brazilian agriculture. The effects of DTM on mitochondrial respiratory parameters and on the organization of artificial and native membranes are described. DTM (200 nmol mg(-1) protein) on isolated liver mitochondria decreased oxygen consumption of both, state III and state IV, as well as the inner mitochondrial membrane potential (Deltapsi). Analysis of segments of the respiratory chain suggested that the DTM inhibition site is located between complex II and complex III. Mitochondrial swelling, energized or driven by the K+ diffusion potential using valinomycin, were partially inhibited by DTM (200 nmol mg(-1) protein). Fluorescence polarization of DPH and DPH-PA, probing the core and outer regions, respectively, of dimyristoylphosphatidylcholine (DMPC) and native mitochondrial membranes, indicated that DTM shifts the midpoint phase transition to lower values, besides broadening the phase transition. DTM decreased the lipid order of DMPC bilayers, at temperatures lower than the transition temperature and also caused a disordering effect on native membranes. However at temperatures above the transition temperature, the pesticide increased the rigidity of the membrane. These results suggest that DTM causes perturbations in lipid-lipid and lipid-protein interactions, interferes in transport mechanisms operating at the membrane level, and causes alterations of membrane permeability and mitochondrial enzyme activities. These effects could be associated with the toxicity of deltamethrin.

3,3',4,4',5-Pentachlorobiphenyl (PCB 126) impacts hepatic lipid peroxidation, membrane fluidity and beta-adrenoceptor kinetics in chick embryos

Polychlorinated biphenyls (PCB) and other aryl hydrocarbon receptor (AHR) agonists induce oxidative stress and alter membrane lipid peroxidation and fluidity. This study tested the hypothesis that PCB-induced changes in membrane properties impact membrane beta-adrenoceptor (beta-AR) affinity and capacity in chick embryo hepatocytes. Embryos were injected into the air cell with 1.6 microg 3,3',4,4',5-pentachlorobiphenyl (PCB 126)/kg egg at day 0, and incubated to day 19 when livers were removed. This dose resulted in hepatic PCB 126 levels of 0.67 ng/g liver or 10.2 ng/g liver lipid; levels in untreated embryos were non-detectable. Hepatic microsomal EROD activity was elevated by approximately 12-fold and embryo mortality was significantly increased compared with the untreated group. Hepatic lipid peroxidation increased and membrane order (steady-state fluorescence anisotropy values) decreased with in ovo PCB 126 exposure. Consistent with changes in membrane structure, hepatic beta-AR affinity for CGP 12177 significantly decreased (Kd increased) without changes in receptor numbers. This study demonstrates that in ovo exposure to PCB 126 in chick eggs significantly impacted embryo survival, and this was correlated with altered hepatic membrane structure and ultimately membrane function.

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.

Interaction of an odorant lactone with model phospholipid bilayers and its strong fluidizing action in yeast membrane

Some odorant lactones are naturally present in fruits or in fermented products; they can also be used as food additives and can be produced by microorganisms at the industrial scale by biotechnological processes. Gamma-decalactone was previously shown to have antimicrobial properties. We determined by infrared spectroscopy measurements that this compound rapidly diffused into model phospholipid bilayers (within 2 min), modifying the general physical state of a dimyristoyl-L-alpha-phosphatidylcholine (DMPC) film. In vivo, the lactone strongly increased membrane fluidity in the model yeast Yarrowia lipolytica, as evaluated by fluorescence anisotropy measurements. This effect was more important than that of benzyl alcohol, which is known as a fluidizing agent in living cells, and may explain the toxic action of gamma-decalactone in microorganisms.

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.

Influence of the physical states of membrane surface area and center area on lysosomal proton permeability

The physical state of the lysosomal membrane was modulated with the membrane fluidizers n-propanol and n-octanol and with the membrane rigidifiers cholesteryl hemisuccinate and cholesterol. Membrane fluidity was examined by the steady-state fluorescence anisotropy of 2-(9-anthroyloxy) palmitic acid and 16-(9-anthroyloxy) palmitic acid. Fluidizing the membranes at the surface and center areas increased the proton permeability coefficient by 92.8 and 18.0%, respectively. Rigidifying the membranes at the surface and center areas decreased the coefficient by 68.2 and 40.2%, respectively. Proton leakage of the lysosomes increased and decreased similar to the coefficient changes with the treatments. The results indicate that lysosomal proton permeability is affected by its membrane's physical state, and the physical state of the membrane surface area affects the proton permeability more markedly. The proton permeability coefficient of liposomes was similar to that of lysosomes, suggesting that efflux of lysosomal protons might occur through the lipid part of the bilayer but not transmembrane proteins.

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.

Changes induced by malathion, methylparathion and parathion on membrane lipid physicochemical properties correlate with their toxicity

Perturbations induced by malathion, methylparathion and parathion on the physicochemical properties of dipalmitoylphosphatidylcholine (DPPC) were studied by fluorescence anisotropy of DPH and DPH-PA and by differential scanning calorimetry (DSC). Methylparathion and parathion (50 microM) increased the fluorescence anisotropy evaluated by DPH-PA and DPH, either in gel or in the fluid phase of DPPC bilayers, but mainly in the fluid phase. Parathion is more effective than methylparathion. On the other hand, malathion had almost no effect. All the three xenobiotics displaced the phase transition midpoint to lower temperature values and broadened the phase transition profile of DPPC, the effectiveness following the sequence: parathion>methylparathion>>malathion. A shifting and broadening of the phase transition was also observed by DSC. Furthermore, at methylparathion/lipid molar ratio of 1/2 and at parathion/lipid molar ratio of 1/7, the DSC thermograms displayed a shoulder in the main peak, in the low temperature side, suggesting coexistence of phases. For higher ratios, the phase transition profile becomes sharp as the control transition, but the midpoint is shifted to the previous shoulder position. Conversely to methylparathion and parathion, malathion did not promote phase separation. The overall data from fluorescence anisotropy and calorimetry indicate that the degree of effect of the insecticides on the physicochemical membrane properties correlates with toxicity to mammals. Therefore, the in vivo effects of organophosphorus compounds may be in part related with their ability to perturb the phospholipid bilayer structure, whose integrity is essential for normal cell function.

Lipid fatty acid and protein pattern of equine prostasome-like vesicles

The semen of several mammals contains vesicles of different composition and origin. We have recently reported on the presence of lipoprotein vesicles in stallion semen. To a certain extent, these resemble human prostasomes, but differ from them in amount and composition. These horse-semen prostasome-like vesicles may be important, not only in horse reproductive physiology, but also in view of stallion semen cryopreservation. In this paper, we have studied horse-semen prostasome-like vesicles and found that they possess less saturated fatty acid than human prostasomes. Moreover, their protein pattern (SDS-PAGE electrophoresis) shows that the 30-50-kDa fraction is less abundant in stallion vesicles. In addition, fluidity (measured as fluorescence anisotropy of diphenylhexatriene) is higher in horse prostasome-like vesicles than in human prostasomes, albeit being much lower than that of most membranes. These findings may be connected to some species-related differences in reproductive physiology: the vaginal milieu of the mare is not acidic and the deposition of semen is intrauterine in the horse but vaginal in humans.

The mechanism for lindane-induced inhibition of steroidogenesis in cultured rat Leydig cells

The in vitro effect of the gamma-isomer of hexachlorocyclohexane, lindane, on rat Leydig cell steroidogenesis was studied. Leydig cells from mature male rats were incubated with human chorionic gonadotropin (hCG, 1 IU) for 3 h at 34 degrees C in the presence of different doses of lindane (2-200 microg/ml; 2-200 ppm). Results demonstrate that lindane produces a dose-dependent inhibition of testosterone production in hCG-stimulated Leydig cells. The decreased testosterone synthesis was accompanied with a half-reduced LH/hCG receptor number without any modification in the K(d) value. In addition, lindane also decreased cAMP production. These effects were not due to a detrimental action of lindane on cell viability. Results of this study demonstrate a direct inhibitory action of lindane on testicular steroidogenesis, at least in part, through a reduction in the classical second messenger production involved in this pathway.

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.

Effect of organochlorine insecticides on nicotinic acetylcholine receptor-rich membranes

The so-called generalized polarization (GP) of the fluorescent probe Laurdan and the steady-state fluorescence anisotropy of the probe diphenylhexatriene (DPH) and its phenylpropionic derivative (PA-DPH) were used to study the effects of several organochlorine insecticides of the chlorophenylethane, chlorinated cyclohexane and chlorinated cyclodiene families on the Torpedo nicotinic acetylcholine receptor (AChR)-rich native membrane. All insecticides, with the exception of Lindane, augmented Laurdan GP both in the native membrane and in model lipid systems. Most organochlorine compounds produced a concentration-dependent decrease of DPH and PA-DPH anisotropy in the AChR-rich membrane. These compounds exhibited a dual behavior vis-à-vis the native AChR-rich membrane, exerting disordering effects at the bilayer core while ordering and/or excluding water molecules from the lipid-protein interface region, as sensed by DPH anisotropy and Laurdan GP, respectively. Furthermore, all insecticides decreased the efficiency of fluorescence resonance energy transfer between the intrinsic protein and Laurdan, albeit to different extents. On the basis of all these observations, the existence of potential target sites for insecticides in the protein-lipid interface region is postulated.

A novel aspect of lindane testicular toxicity: in vitro effects on peritubular myoid cells

The in vitro effects of the insecticide lindane have been investigated in rat testis peritubular myoid cells (PMCs). Upon PMC exposure to lindane, polarity increase and decrease of dipole dynamics were seen at the membrane level (EC50 20 microM), leading to a partial dissipation of the membrane intrinsic dipole potential. The initial membrane depolarization was increased by Cl- efflux and limited by Ca(2+)-activated repolarizing currents. Concomitantly, lindane produced an increase in [Ca2+]i (EC50 125 microM) resulting from both Ca2+ release from an inositol 1,4,5-trisphosphate-sensitive intracellular store and a voltage-dependent Ca2+ influx from the extracellular medium. Of particular interest from a toxicologic point of view, insecticide concentrations well below those effective in altering ion homeostasis potently inhibited both [Ca2+]i increase and contraction induced by the natural agonists vasopressin and endothelin-1 (IC50s < 10 microM). These data demonstrate that PMCs are highly susceptible to lindane and suggest that the insecticide may exert testicular toxicity by interfering with hormone-regulated PMC function.

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.

Alterations in rat erythrocyte membrane due to hexachlorocyclohexane (technical) exposure

1. Hexachlorocyclohexane (HCH), an organochlorine pesticide having hydrophobic molecule is known to act on membranes. HCH mediated alterations in erythrocyte membrane occur through disorganization of the lipid bilayer. Therefore the changes in erythrocyte membrane fluidity, osmotic fragility and certain membrane bound enzymes were studied. Administration of HCH (technical) to rats at 5 mg/kg, orally, 5 days a week for 1, 2 and 3 months caused marked increase in erythrocyte membrane fluidity, osmotic fragility and decrease in levels of Na+, K(+)-ATPase, acetylcholinesterase in erythrocytes and glutathione in blood. 2. These changes indicate that HCH adversely affects membrane structure and function.

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.

Phase behavior and permeability properties of phospholipid bilayers containing a short-chain phospholipid permeability enhancer

The thermodynamic phase behavior and trans-bilayer permeability properties of multilamellar phospholipid vesicles containing a short-chain DC10PC phospholipid permeability enhancer have been studied by means of differential scanning calorimetry and fluorescence spectroscopy. The calorimetric scans of DC14PC lipid bilayer vesicles incorporated with high concentrations of DC10PC demonstrate a distinct influence on the lipid bilayer thermodynamics manifested as a pronounced freezing-point depression and a narrow phase coexistence region. Increasing amounts of DC10PC lead to a progressive lowering of the melting enthalpy, implying a mixing behavior of the DC10PC in the bilayer matrix similar to that of a substitutional impurity. The phase behavior of the DC10PC-DC14PC mixture is supported by fluorescence polarization measurements which, furthermore, in the low-temperature gel phase reveal a non-monotonic concentration-dependent influence on the structural bilayer properties; small concentrations of DC10PC induce a disordering of the acyl chains, whereas higher concentrations lead to an ordering. Irreversible fluorescence quench measurements demonstrate a substantial increase in the trans-bilayer permeability over broad temperature and composition ranges. At temperatures corresponding to the peak positions of the heat capacity, a maximum in the trans-bilayer permeability is observed. The influence of DC10PC on the lipid bilayer thermodynamics and the associated permeability properties is discussed in terms of microscopic effects on the lateral lipid organization and heterogeneity of the bilayer.

Partition of the organochlorine insecticide lindane into the human sperm surface induces membrane depolarization and Ca2+ influx

The effects of the insecticide lindane (the gamma-isomer of 1,2,3,4,5,6-hexachlorocyclohexane) on membrane potential, cytosolic free Ca2+ concentration ([Ca2+]i) and surface biophysical properties were studied in human spermatozoa. The insecticide induces rapid, transient and reproducible membrane depolarization and opening of voltage-dependent Ca2+ channels leading to an increase in [Ca2+]i. In contrast with the effect in somatic cells, lindane did not affect gamma-aminobutyric acid receptor-linked Cl- currents. Ca2+ and K+ currents were found to drive lindane-induced membrane depolarization and repolarization respectively, whereas Na+ and Cl- fluxes appear not to have a role in the phenomenon. The insecticide was still able to produce membrane depolarization both in the combined absence of extracellular Ca2+ and Na+ and in high-K+ buffer, suggesting that lindane alters the membrane dipole potential. In agreement with this, Laurodan and Prodan fluorescence spectroscopy revealed that lindane partition into the sperm plasma membrane lowers water molecular dynamics in the uppermost region of the membrane external leaflet, probably as the result of reordering of water dipoles. We propose that the first effect of lindane partitioning into the sperm plasma membrane is a change in the membrane dipole potential, which results in the activation of membrane-located Ca2+-influx pathways.

Red blood cell ghosts are affected by adrenoleucodystrophy

X-linked adrenoleucodystrophy is a disorder occurring in different clinical forms, characterized by adrenal, gonadal and nervous system dysfunction. The basis of the illness is a derangement of the peroxisomal system necessary to oxidize very long-chain fatty acids that accumulate in various tissues. The diagnosis relies on clinical signs and symptoms and on biochemical findings. The six reported cases presented idiopathic adrenal insufficiency. We measured the lipid composition of red blood cell (RBC) ghosts of patients and control subjects. The distribution of phosphorus among phospholipid classes was unaffected; we could not demonstrate any differences between the fatty acid patterns of RBC membrane, either in total lipid extracts or in separated lipid classes. However, we found an increase in total lipid (both phospholipid and cholesterol), in membrane viscosity and in the Na+/K(+)-dependent ATPase. Therefore, we report four main findings on ghosts in adrenoleucodystrophy patients: (a) very long-chain fatty acids do not accumulate; (b) the lipid-protein ratio increases; (c) fluidity decreases; and (d) the activity of ATPase increases. The last finding is proposed as a possible biochemical marker of the illness. We conclude that adrenoleucodystrophy affects deeply RBC membranes.

Lindane suppresses the lipid-bilayer permeability in the main transition region

The effects of a small molecule, the insecticide lindane, on unilamellar DMPC bilayers in the phase transition region, have been studied by means of differential scanning calorimetry and fluorescence spectroscopy. The calorimetric data show that increasing concentrations of lindane broaden the transition and lower the transition temperature, without changing the transition enthalpy significantly. Lindane therefore enhances the thermal fluctuations of the bilayer. The calorimetric data furthermore suggest that the bilayer structure is intact and not disrupted by even high concentrations (32 mol%) of lindane. Fluorescence spectroscopy was used to measure the passive permeability of unilamellar DMPC bilayers to Co2+ ions. The data show that lindane seals the bilayer for Co2+ penetration and that this effect increases with increasing lindane concentration. The results are discussed in relation to the effects on the permeability of other small molecules, e.g., anesthetics.

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.

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.

Influence of hyperthyroidism on lindane-induced hepatotoxicity in the rat

Parameters related to hepatic oxidative stress, cell injury, phagocytic activity, and liver histology were studied in control rats and in animals subjected to L-3,3',5-triiodothyronine (T3) and/or lindane administration. Hyperthyroidism elicited a calorigenic response and increased rates of hepatic O2 uptake, which were not modified by lindane treatment. T3 diminished serum lindane levels as well as those in the liver and adipose tissue, whereas lindane enhanced serum T3 levels in animals given T3. Compared with control rats, lindane significantly increased the rate of formation of thiobarbituric acid reactants (TBARS) by the liver, with no changes in either the reduced glutathione (GSH) content, the TBARS/GSH ratio as indicator of oxidative stress, or in the fractional rates of lactate dehydrogenase (LDH) and GSH efflux from perfused livers as integrity parameters. Hyperthyroidism induced GSH depletion in the liver, with a significant enhancement in the TBARS formation, the TBARS/GSH ratio, and in the fractional LDH and GSH efflux. These parameters were increased further by joint T3 and lindane administration in a magnitude exceeding the sum of the effects produced by the separate treatments. In addition, hyperthyroidism led to Kupffer cell hyperplasia and significant increases in serum glutamate oxalacetate transaminase (GOT) and in hepatic zymosan-induced chemiluminescence, while liver myeloperoxidase (MPO) activity was found unchanged, compared with controls. Rats treated with lindane presented normal liver histology, with no changes in biochemical parameters related to cell injury. The joint administration of T3 and lindane, however, elicited a marked elevation in serum GOT and glutamate pyruvate transaminase (GPT), concomitantly with extensive liver necrosis and the presence of granulomas containing lymphocytes, Kupffer cells and polymorphonuclear leukocytes (PMN). In this condition, hepatic zymosan-induced light emission and MPO activity were enhanced over control values. It is concluded that hyperthyroidism increases the susceptibility of the liver to the toxic effects of lindane, which seems to be accomplished by potentiation of the hepatic oxidative stress status. The latter effect may be conditioned by an enhanced phagocytic respiratory burst activity due to the observed Kupffer cell hyperplasia and PMN infiltration, in addition to the increased production of reactive oxygen species in parenchymal cells.

Partition of DDE in synthetic and native membranes determined by ultraviolet derivative spectroscopy

Partition coefficients of DDE (2,2-bis(p-chlorophenyl)-1,1-dichloroethylene) were determined, in model and native membranes, as a function of temperature, lipid chain length, cholesterol content and DDE concentration, by means of second derivative ultraviolet spectrophotometry. DDE incorporation increases with the temperature, since the partition values in dimyristoylphosphatidylcholine (DMPC), at 24, 30 and 37 degrees C, are 5722 +/- 138, 10356 +/- 763 and 14006 +/- 740, respectively. The insecticide incorporates better into bilayers of DMPC as compared with DPPC (dipalmitoylphosphatidylcholine). The partition decreases from 10355 +/- 763 in DMPC to 6432 +/- 613 in DPPC, at temperatures 5-7 degrees C above the midpoint of their transitions. The addition of cholesterol to fluid membranes of DMPC depresses the partition of DDE. In agreement with the results in models of synthetic lipids, the partition of DDE into native membranes increases with the temperature and decreases with the intrinsic cholesterol. It is concluded that a fluid membrane favors the accumulation of DDE.

Hexachlorocyclohexanes affect the arachidonic acid release from phosphatidylinositol but not from other phospholipid classes in tubular cell cultures

Gamma- and delta-isomers of hexachlorocyclohexane caused marked decreases in the levels of radioactive phospholipids, and increases in the levels of [3H]arachidonate incorporated into free fatty acids in rat renal tubular cells. The increased radioactivity of free fatty acids arises from the decrease of [3H]arachidonate incorporated into phosphatidylinositol, but not into phosphatidylcholine, phosphatidylserine or phosphatidylethanolamine. This fact suggests that phosphatidylinositol can be broken down to the fatty acid from the sn-2 position and lysophospholipid by a phospholipase activity increased by hexachlorocyclohexanes. The observed specific toxicant action could be achieved in two ways: (a) operating upon a specific phospholipase A2 that acts on phosphatidylinositol, but not on other phospholipids as substrates and/or (b) involving substrate-phospholipase A2 interactions. Interestingly, the observed effect of the delta-isomer was more pronounced than that of the gamma-one.

Mechanisms of membrane toxicity of hydrocarbons

Microbial transformations of cyclic hydrocarbons have received much attention during the past three decades. Interest in the degradation of environmental pollutants as well as in applications of microorganisms in the catalysis of chemical reactions has stimulated research in this area. The metabolic pathways of various aromatics, cycloalkanes, and terpenes in different microorganisms have been elucidated, and the genetics of several of these routes have been clarified. The toxicity of these compounds to microorganisms is very important in the microbial degradation of hydrocarbons, but not many researchers have studied the mechanism of this toxic action. In this review, we present general ideas derived from the various reports mentioning toxic effects. Most importantly, lipophilic hydrocarbons accumulate in the membrane lipid bilayer, affecting the structural and functional properties of these membranes. As a result of accumulated hydrocarbon molecules, the membrane loses its integrity, and an increase in permeability to protons and ions has been observed in several instances. Consequently, dissipation of the proton motive force and impairment of intracellular pH homeostasis occur. In addition to the effects of lipophilic compounds on the lipid part of the membrane, proteins embedded in the membrane are affected. The effects on the membrane-embedded proteins probably result to a large extent from changes in the lipid environment; however, direct effects of lipophilic compounds on membrane proteins have also been observed. Finally, the effectiveness of changes in membrane lipid composition, modification of outer membrane lipopolysaccharide, altered cell wall constituents, and active excretion systems in reducing the membrane concentrations of lipophilic compounds is discussed. Also, the adaptations (e.g., increase in lipid ordering, change in lipid/protein ratio) that compensate for the changes in membrane structure are treated.

Amiodarone effects on membrane organization evaluated by fluorescence polarization

The effects of amiodarone (0-100 microM) on the physical state of synthetic and native membranes were investigated by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), probing the bilayer core, and of its anionic propionic acid derivative (DPH-PA), probing the outer regions of the bilayer. In the gel phase of dimyristoylphosphatidylcholine (DMPC) bilayers, amiodarone broadens the transition profile and shifts the phase transition midpoint to lower temperature values, as evaluated by both probes. On the other hand, the drug orders the fluid phase of the lipid either in hydrophobic core or in the outer regions of the bilayer, as detected by DPH and DPH-PA, respectively. The effects of amiodarone on the thermotropic behaviour of DPPC confirm and extend data in DMPC. Cholesterol concentration modulates to a great extent the effects of amiodarone in the fluid phase of DMPC. Thus, both probes, DPH and DPH-PA, detect either ordering effects of amiodarone for low cholesterol concentrations (< or = 20 mol%) or disordering amiodarone effects at higher cholesterol levels (> 20 mol%). In agreement with the results in models of synthetic lipids, the ordering effects of amiodarone in fluid native membranes of mitochondria and brain microsomes are depressed with the increase in intrinsic cholesterol. The ordering effects in mitochondria may induce bioenergetic dysfunctions and consequently disturbances in the electromechanic functioning of myocardium.

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.