Interaction Of DDT Research Articles

Mechanistic studies on the DDT-induced inhibition of intercellular communication

Two structurally unrelated compounds, 1,1'-(2,2,2-trichloroethylidene) bis(4-chlorobenzene) (DDT) and 12-O-tetradecanoylphorbol-13-acetate (TPA), are both potent inhibitors of cell-cell communication in vitro as well as tumour promoters in vivo. There is evidence that TPA acts via a specific receptor mechanism involving activation of protein kinase C (pkC). The mechanism of action of DDT has been discussed in terms of membrane perturbation, increased intracellular calcium, interaction with calmodulin and decreased cAMP levels. In the present study the objective was to examine the potential role of pkC activation in DDT-induced inhibition of intercellular communication in cultured cells. The V79 metabolic cooperation assay was used for measuring intercellular communication. Furthermore, the effects of DDT on the activity of partially purified pkC from V79 cells was measured, as was the interaction of DDT with the phorbol ester/DAG-binding site on the pkC enzyme. Results from the biochemical studies showed that DDT neither activates pkC nor binds to the phorbol ester/DAG-binding site, as measured by displacement of PDBU binding. Using the metabolic cooperation assay it was demonstrated that pretreatment with TPA made cells refractory, i.e. a second application of TPA did not inhibit cell-cell communication. DDT added to cells down-regulated with TPA inhibited cell-cell communication, even though these cells were refractive to TPA. This result further supports the hypothesis that DDT and TPA inhibit intercellular communication primarily by different pathways. At non-cytotoxic concentrations, pkC inhibitors (H7, W7 and palmitoyl carnitine) did not affect the TPA- or DDT-induced inhibition of cell-cell communication in the V79 metabolic cooperation assay. Quercetin, a pkC inhibitor which has been reported to eliminate DDT- or TPA-induced inhibition of intercellular communication, was investigated in an in vivo study that measured promotion of enzyme-altered foci in DEN-treated rat liver. Quercetin co-administered with DDT did not act as an antipromoter.

The role of lipid fluidity in the interaction of DDT and some analogs with synthetic membranes

The incorporation of two active chlorinated hydrocarbon insecticides (DDT and MeOC) and inactive DDE into vesicles of DPPC, DMPC, DOPC, and egg PC was studied by discontinuous sucrose gradient centrifugation. The extent of incorporation was used in the calculation of their partition coefficients and solubility in phospholipids. A fluid bilayer was essential for high incorporation. The partition coefficients and membrane saturation capacities were higher in fluid than in rigid membranes. Depending on the chemical, the lipid/aqueous partition coefficients were one to three orders of magnitude lower than the octanol/water partition coefficient. No significant difference was noted in these parameters for the three chemicals even though their hydrophobicities, as judged by their water solubilities, differed by about two orders of magnitude, suggesting that hydrophobicity does not ensure high lipophilicity. Furthermore the lack of correlation between these parameters and insecticidal activity indicates that the biological activities of these insecticides is not the result of specific interactions with the membrane lipids per se. A comparison of literature data with respect to the relative fluidity of various insect and mammalian membranes shows that insect membranes are strikingly more fluid. This would favor greater accumulation of chlorinated hydrocarbons into the unsaturated membranes as the first step in their action on a membrane-associated target site(s), and perhaps would partially explain their generally higher toxicity to insects.

X-ray studies on phospholipid bilayers. V. Interactions with DDT.

The possible interaction of DDT with the lipids dimyristoyl lecithin (DML), dipalmitoylphosphatidylethanolamine (DPPE) and tripalmitin (TP) was studied. The work was carried out on oriented films and crystalline powders of DDT-lipid mixtures at different molar ratios by X-ray diffraction techniques. The diagrams showed only the patterns of pure DDT and that of the corresponding lipid. It is concluded that new phases were not formed and, therefore, no interactions occurred.

Interaction of DDT and pyrethroids with calmodulin and its significance in the expression of enzyme activities of phosphodiesterase

To understand the significance of the inhibitory action of 1,1,1-trichloro-2,2-bis( p-chlorophenyl)ethane (DDT) and pyrethroid insecticides on calmodulin, a universal Ca 2+ binding protein, a bovine heart phosphodiesterase-calmodulin system was studied. It was found that, at concentrations of less than 10 −5M, the inhibitory action of DDT of the phosphodiesterase was due entirely to its action on calmodulin alone. Cypermethrin was less potent than DDT, but it also affected only calmodulin. Permethrin was the most potent inhibitor affecting calmodulin and, to a lesser extent, phosphodiesterase. The inhibitory action of these insecticides on calmodulin raises a possibility that many unsuspected Ca 2+-related systems are being affected by these insecticidal chemicals, as calmodulin is known to play vital roles in many biological reactions dependent upon Ca 2+. These include modulation of phosphodiesterase, neurotransmitter release, adenylate cyclase, Ca 2+-dependent protein kinase, myosine light chain kinase and various membrane phosphorylation systems.

Interaction of the chlorinated hydrocarbon insecticide lindane or DDT with lipids—A differential scanning calorimetry study

The interaction of DDT and lindane with glycosphingolipids and phospholipids was investigated by employing differential scanning calorimetry. The degree of perturbation produced by lindane is stronger than that of DDT and depends also on the lipid.

Interaction of the insecticide 1,1,1-trichloro-2,2-bis( p-chlorophenyl)ethane with the β-receptor adenylate cyclase system in chang liver cell membranes

Interaction of the insecticide 1,1,1-trichloro-2,2-bis-( p-chlorophenyl)ethane (DDT) with β-receptor binding and adenylate cyclase activity of biological membranes has been studied. Following exposure of cultured Chang liver cells to DDT, maximal binding of the catecholamine antagonist [ 125I]iodohydroxybenzylpindolol (HYP) to isolated cell membranes was decreased by 30% whereas the dissociation constant remained unchanged. Both basal activity and maximal isoproterenol-stimulated activity of adenylate cyclase were not altered. The isoproterenol concentration required for half-maximal stimulation of the enzyme was increased about 2-fold as was the agonist concentration required for half-maximal displacement of the antagonist HYP at the β-receptor binding site. Thus, coupling efficiency of hormone-stimulated adenylate cyclase activity was not influenced by the presence of DDT in these membranes. The data show that interaction of DDT with the β-receptor adenylate cyclase complex is restricted to the receptor component. Enzyme activity is directly linked to changes of agonist binding at the β-receptor. Interference of DDT with signal transuction via ‘fluidization’ of membrane lipids has not been detected.

Interaction of DDT with sodium channels in squid giant axon membranes

The effects of DDT on the sodium channel gating mechanism were studied with internally perfused squid giant axons under voltage clamp conditions. In contrast to earlier studies, DDT has pronounced effects on the sodium conductance system of squid axons. Internal application of 1 × 10 −4M DDT had no effect on the activation time constant (τ m) or on the peak current, but the falling phase of the sodium current and the tail current upon repolarization were slowed dramatically (τ tail= 3–13 ms). The sodium inactivation process became second order after DDT treatment. The time constant of the fast phase (τ 1) was identical to τ h recorded in the control axon, while the time constant of the slow phase (τ 2) was more than 10 times greater. The voltage dependence of τ 2 was different from τ h, increasing with depolarization. The steady-state inactivation curve was shifted in the direction of hyperpolarization by 6–8 mV, but even after prolonged depolarizing pulses, the sodium conductance did not inactivate completely. These data are consistent with the hypothesis that a population of sodium channels modified by DDT activates normally but is then retained in a second open state which inactivates slowly.

The interaction of ddt with suspended particles in sea water

The equilibrium distribution of DDT between the liquid and solid phases in the sea water medium was investigated by means of the radiotracer technique. The investigation of the influence of DDT concentration on its adsorption on several solid phases is presented and results are given as adsorption isotherms. Desorption experiments indicate that these processes are reversible. Extension of desorption is higher from quartz than from limestone, while it is significantly lower than from marine sediments. Examination of the equilibrium distribution of DDT between sea water and the examined surfaces suggested that DDT in the investigated systems exists as a colloid dispersion. The results are also discussed from the point of view of marine pollution. Suggestions for the future work in this field are also given.

An interaction of DDT in the metabolism of essential fatty acids.

AbstractThe growth of female rats was depressed further by the incorporation of DDT into a ration deficient in essential fatty acids (EFA). With female rats fed a ration supplemented with EFA, DDT produced a slight stimulation in growth. DDT also produced an increase in the 20∶3ω9/20∶4ω6 ratio in liver lipids of male rats fed a ration deficient in EFA. These data indicate an effect in EFA nutrition. Substantial changes in the fatty acid composition of liver lipids resulted from the feeding of DDT. The proportion of 16∶0 was decreased, while that of 18∶0 was increased. With rats on the supplemented rations an increase in the proportion of 20∶4ω6 was observed, while in the deficient rats a comparable increase was observed in the proportion of 20∶3ω9. These changes in fatty acid composition have been related to the proliferation of hepatic smooth endoplasmic reticulum induced by the DDT, and it is suggested that this effect could increase the demand for EFA by the liver, thus influencing EFA nutrition.

Ionic channels and nerve membrane lipoproteins: DDT-nerve membrane interaction.

DDT inhibits the potassium current and delays the turning off process of the sodium current in voltage-clamped axons. In order to identify the target sites of DDT in nerve membranes, experiments were performed so as to investigate (i) the accumulation of 14C DDT in nerve fiber plasma membranes of the squid Dosidicus gigas and (ii) the interaction of DDT with isolated nerve membranes, their lipid constituents and membrane proteins. Two nerve membrane fractions were used: fraction I tentatively identified as the axolemma, and fraction II as the plasma membranes of the satellite cells, including Schwann cells. The interaction of DDT with human high density lipoprotein (HDL) and lipid-free apolipoprotein (apo-HDL), was also investigated. The monolayer technique and the spectrophotofluorometric method were used. The results show that DDT accumulates in the plasma membranes of the nerve fibers. They also indicate that DDT causes a reduction in the fluorescence intensity of the protein aromatic residues which is...

Interaction of DDT and the gastrointestinal microflora of the rat.

Interaction of DDT and the gastrointestinal microflora of the rat.

Interaction of DDT with the components of lobster nerve membrane conductance.

The falling phase of action potential of lobster giant axons is markedly prolonged by treatment with DDT, and a plateau phase appears as in cardiac action potentials. Repetitive afterdischarge is very often superimposed on the plateau. Voltage-clamp experiments with the axons treated with DDT and with DDT plus tetrodotoxin or saxitoxin have revealed the following: DDT markedly slows the turning-off process of peak transient current and suppresses the steady-state current. The falling phase of the peak transient current in the DDT-poisoned axon is no longer expressed by a single exponential function as in normal axons, but by two or more exponential functions with much longer time constants. The maximum peak transient conductance is not significantly affected by DDT. DDT did not induce a shift of the curve relating the peak transient conductance to membrane potential along the potential axis. The time to peak transient current and the time for the steady-state current to reach its half-maximum are prolonged by DDT to a small extent. The finding that, under the influence of DDT, the steady-state current starts flowing while the peak transient current is partially maintained supports the hypothesis of two operationally separate ion channels in the nerve membrane.