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Using an isotope labelling technique it has been shown that an organophosphorus insecticide methylparathion (0,0-diethyl 0-4-nitrophenyl phosphorothioate) depressed calcium uptake by sarcoplasmic reticulum isolated from rabbit hind leg muscle. The effect was significant for insecticide concentrations of 50 and 100 µM and was dose-dependent The insecticide exerted a more pronounced effect on calcium uptake in the presence of ATP in the reticulum environment than in the absence of ATP. The inhibitory action of methylparathion on Ca2+ accumulation by sarcoplasmic reticulum can cause a rise in myoplasmic free Ca2+, the essential prerequisite for contracture activation. Because methylparathion, as well as other organophosphorus insecticides, is primarily neurotoxic, evidence of non-specific effect could be important for assessing its environmental safety.
The interaction of methylbromfenvinfos with model and native membranes was investigated using fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), a probe located in the hydrophobic core of the bilayer and l,3-bis-(l-pyrene) propane, a probe distributed in the outer region of the bilayer. DPH reported a broadening of the transition profile and solidifying effects in the fluid phase of liposomes formed from dimyristoyl (DMPC), dipalmitoyl (DPPC), and distearoyl (DSPC) phosphatidylcholine in the presence of 50 μM of the insecticide. Py(3)Py detected an ordering effect of the insecticide in the fluid state of the lipids and abolished pretransition in DPPC and DSPC vesicles. Cholesterol added to DMPC decreased the influence of the insecticide. The effect of methylbromfenvinfos on the fluidity of some native membranes, namely erythrocytes, lymphocytes, brain microsomes, and sarcoplasmic reticulum, depended on the cholesterol content of these membranes.
The organophosphorus insecticide bromfenvinios and its methylated homologue methylbrom- fenvinfos inhibited the activity of pig kidney (Na++K+)-ATPase contained in the microsomal fraction and purified from it. The effect was dose-dependent Subrate kinetic studies of the enzyme revealed the existence of two active sites with high and low affinity to ATP respectively. The Dixon analysis of the mode of inhibition indicated its noncompetitive character. The inhibition was more pronouced for bromfenvinfos than for methylbromfenvinfos and the purified enzyme was more affected than the enzyme contained in the microsomal fraction. The Hill plot of inhibition indicated a multisite binding of both insecticides exhibiting cooperativity in binding. The Hill coefficient (n) fulfilled the relationship 1 < n < 3. These properties of the interaction suggest an allosteric nature of the inhibitory action of the insecticides. An indirect mechanism of the interaction was proposed: methylparathion could inhibit the activity of the (Na+ + K+)-ATPase by excluding the enzyme protein from its normal lipid milieu.
The organophosphorus insecticide bromfenvinfos (2-bromo-l-(2,4-dichlorophenyl)vinyl diethyl phosphate) and its methylated homologue methylbromfenvinfos inhibited noncompetitively the activity of (Ca2+ + Mg2+)-ATPase bound to and solubilized from pig erythrocyte membrane. Both enzyme preparations exhibited biphasic substrate curves displaying the existence of two functional active sites with low and high affinity to ATP. Inhibition of activity was more pronounced for bromfenvinfos than for methylbromfenvinfos and the solubilized enzyme preparation was more affected than the bound one. The results of the experiment suggest that the insecticides inhibited the ATPase by binding to a site on the enzyme rather than by interaction with associated lipids, although their presence could weaken the action of the compounds due to the stronger affinity of organophosphorus insecticides for lipids rather than for proteins.
The effect of organophosphorus insecticides malathion and parathion as well as their main metabolites malaoxon and paraoxon on chloride (36Cl-) and sulfate (35SO42-) equilibrium exchange in pig erythrocytes was investigated using an isotope labelling technique. Efflux of both radioactive isotopes vs. time followed a single exponential. Parathion and paraoxon inhibited the chloride equilibrium exchange in intact ceils in a dose- and time-dependent manner. There was no difference between effects evoked by these two compounds. Neither malathion nor malaoxon affected the chloride transport. Parathion and paraoxon inhibited sulfate efflux from resealed ghosts. The effect was also dose- and time-dependent. Again, there was no difference between action of the agents. No effect of malathion and malaoxon on sulfate efflux was observed. Dixon analysis revealed noncompetitive character of the inhibition of the exchange of both anions with the apparent Ki, values 68 and 73 µM for parathion and paraoxon, respectively in the case of chloride transport; for sulfate exchange these values were 341 and 340 µM, respectively. It was suggested that structural similarity between parent agents and their metabolites is responsible for the identity of their effects. Parathion and paraoxon could inhibit the anion exchange indirectly by changing the fluidity of the erythrocyte membrane or directly by binding to the Band 3 protein and evoking conformational changes leading to the inhibition of the anion transport. The insecticides, due to their ability to phosphorylate, could also disturb some regulation processes in the Band 3 protein.
Cadmium is a widespread environmental and occupational pollutant and quercetin is a dietary flavonoid, which is reported to modulate the effects of many mutagens and carcinogens. We investigated the ability of cadmium chloride to induce DNA damage in human lymphocytes in the presence of quercetin using the alkaline comet assay. Cadmium chloride (5-150 muM) evoked dose-dependent DNA damage and quercetin at 50 muM decreased the extent of the damage. The lymphocytes exposed to cadmium chloride were able to remove their DNA damage within a time period shorter than 120 min. The cells treated with quercetin at 50 muM prior to exposure to cadmium required shorter periods of time to recover. Quercetin could chelate cadmium ions, scavenge free radicals produced by cadmium or regenerate cellular DNA-repair enzymes.
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