Tefluthrin modulates a novel anionic background conductance (I(AB)) in guinea-pig ventricular myocytes

Tefluthrin: metabolism, food residues, toxicity, and mechanisms of action

Tefluthrin is a Type I pyrethroid insecticide widely used all over the world. Residues of tefluthrin in various agricultural and animal-derived products may be related to potential human health risks. Tefluthrin metabolism in mammals involves hydrolysis of the ester bond to form cyclopropane acid and 4-methylbenzyl alcohol moieties, followed by oxidation. In this review manuscript, we provide crucial information regarding the toxicity of pyrethroids and propose natural antioxidants for amelioration poisoning in humans and animals. We call for the rational use of tefluthrin as an agrochemical product and for greater attention to the residual toxicity caused by tefluthrin in primary and succeeding crops. This greater attention is required given the global use of tefluthrin.

ClC-3 is a main component of background chloride channels activated under isotonic conditions by autocrine ATP in nasopharyngeal carcinoma cells

In this study, the activation mechanisms of the background chloride current and the role of the current in maintaining of basal cell volume were investigated in human nasopharyngeal carcinoma CNE-2Z cells. Under isotonic conditions, a background chloride current was recorded by the patch clamp technique. The current presented the properties similar to those of the volume-activated chloride current in the same cell line and was inhibited by chloride channel blockers or by cell shrinkage induced by hypertonic challenges. Extracellular applications of reactive blue 2, a purinergic receptor antagonist, suppressed the background chloride current in a concentration-dependent manner under isotonic conditions. Depletion of extracellular ATP with apyrase or inhibition of ATP release from cells by gadolinium chloride decreased the background current. Extracellular applications of micromolar concentrations of ATP activated a chloride current which was inhibited by chloride channel blockers and hypertonic solutions. Extracellular ATP could also reverse the action of gadolinium chloride. Transfection of CNE-2Z cells with ClC-3 siRNA knocked down expression of ClC-3 proteins, attenuated the background chloride current and prevented activation of the ATP-induced current. Furthermore, knockdown of ClC-3 expression or exposures of cells to ATP (10 mM), the chloride channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and tamoxifen, or reactive blue 2 increased cell volume under isotonic conditions. The results suggest that ClC-3 protein may be a main component of background chloride channels which can be activated under isotonic conditions by autocrine/paracrine ATP through purinergic receptor pathways; the background current is involved in maintenance of basal cell volume.

Molecular mechanisms of pyrethroid insecticide neurotoxicity: recent advances

Synthetic pyrethroid insecticides were introduced into widespread use for the control of insect pests and disease vectors more than three decades ago. In addition to their value in controlling agricultural pests, pyrethroids are at the forefront of efforts to combat malaria and other mosquito-borne diseases and are also common ingredients of household insecticide and companion animal ectoparasite control products. The abundance and variety of pyrethroid uses contribute to the risk of exposure and adverse effects in the general population. The insecticidal actions of pyrethroids depend on their ability to bind to and disrupt voltage-gated sodium channels of insect nerves. Sodium channels are also important targets for the neurotoxic effects of pyrethroids in mammals but other targets, particularly voltage-gated calcium and chloride channels, have been implicated as alternative or secondary sites of action for a subset of pyrethroids. This review summarizes information published during the past decade on the action of pyrethroids on voltage-gated sodium channels as well as on voltage-gated calcium and chloride channels and provides a critical re-evaluation of the role of these three targets in pyrethroid neurotoxicity based on this information.

Differential pharmacology of the cardiac anionic background current I(AB)

A novel anionic background conductance (I(AB)) in cardiac ventricular myocytes has recently been identified but at present there is comparatively little information on its pharmacological modulation. This study investigated the effects of on I(AB) of four pyrethroid agents tefluthrin (a selective activator of this current), tetramethrin, fenpropathrin and alpha-cypermethrin in addition to other well known chloride channel modulators (chlorotoxin, gadolinium and picrotoxin). Guinea-pig ventricular myocytes were isolated using an enzymatic and mechanical dispersion procedure and all electrophysiological measurements were made using the whole-cell patch-clamp technique. In contrast to other anion conductances (stretch- or volume-regulated chloride current (I(Cl,vol)), a cAMP-dependent Cl(-) current (I(Cl,cAMP))) I(AB) was augmented by tefluthrin, fenpropathrin, alpha-cypermethrin (but not tetramethrin). I(AB) was insensitive to chlorotoxin, gadolinium and picrotoxin. Thus, I(AB) exhibits a distinct pharmacological profile from other known cardiac anion conductances.

An outwardly rectifying anionic background current in atrial myocytes from the human heart

This report describes a hitherto unreported anionic background current from human atrial cardiomyocytes. Under whole-cell patch-clamp with anion-selective conditions, an outwardly rectifying anion current (I_ANION) was observed, which was larger with iodide than nitrate, and with nitrate than chloride as charge carrier. In contrast with a previously identified background anionic current from small mammal cardiomyocytes, I_ANION was not augmented by the pyrethroid tefluthrin (10 μM); neither was it inhibited by hyperosmolar external solution nor by DIDS (200 μM); thus I_ANION was not due to basal activity of volume-sensitive anion channels. I_ANION was partially inhibited by the Cl⁻ channel blockers NPPB (50 μM) and Gly H-101 (30 μM). Incorporation of I_ANION into a human atrial action potential (AP) simulation led to depression of the AP plateau, accompanied by alterations to plateau inward calcium current, and to AP shortening at 50% but not 90% of complete repolarization, demonstrating that I_ANION can influence the human atrial AP profile.

Differential effects of pyrethroids on volume-sensitive anion and organic osmolyte pathways

1. There are no effective ways of screening for potential modulators of volume-regulated anion channels in their native cell type. Generally, cell lines are used for this purpose. Using HeLa and C6 glioma cells, we identified the pyrethroids as a novel class of compounds that inhibit taurine efflux through volume-regulated anion transport pathways in these cells. Subsequently, we examined their effects on volume-regulated anion channels in guinea-pig ventricular myocytes to determine whether results obtained using cell lines could be extrapolated to other tissues. 2. Tetramethrin inhibited taurine efflux in both HeLa and C6 glioma cells with Ki values of approximately 26 and 16 micro mol/L, respectively. Bioallethrin and fenpropathrin inhibited volume-sensitive taurine efflux from C6 glioma cells, but not from HeLa cells. The Ki values for bioallethrin and fenpropathrin were 70 and 59 micro mol/L, respectively. 3. Volume-sensitive I- efflux was observed in HeLa cells but not in C6 glioma cells, suggesting that the taurine efflux pathway in C6 glioma cells may be different to that of the I- efflux pathway. Cyfluthrin, tetramethrin, fenpropathrin, tefluthrin and bioallethrin all significantly inhibited volume-sensitive I- efflux from HeLa cells at 100 micro mol/L. 4. Patch-clamp experiments have shown inhibition of ICl,vol in guinea-pig ventricular myocytes by fenpropathrin, but not tetramethrin or cypermethrin, at 100 micro mol/L. This revealed that further differences exist between ICl,vol in guinea-pig ventricular myocytes and the anion transport pathways in C6 glioma and HeLa cells. 5. In conclusion, we have shown that pyrethroids differentially inhibit volume-regulated anion and taurine efflux in a number of cell types. Because these compounds have different effects in different cells, it is likely that: (i) more than one pathway is involved in the volume-sensitive transport of anions and organic osmolytes; and (ii) the molecular identities of the channels underlying anion transport are different. Finally, for the reasons given above, care should be taken when extrapolating data from one cell type to another. However, in the absence of an existing high-throughput screen, taurine efflux still represents a viable route for the identification of potential modulators of volume-regulated ion channels.

Inhibitory effects of the antiestrogen agent clomiphene on cardiac sarcolemmal anionic and cationic currents

The aim of this study was to determine the effects of the antiestrogen agent clomiphene on cardiac anionic and cationic sarcolemmal ion channels. Whole-cell recordings were made from rat and guinea pig ventricular myocytes. Clomiphene inhibited the volume-regulated chloride current [I(Cl,vol), activated by cell swelling after hypotonic shock (approximately 145 mOsM)] with an IC(50) value of approximately 9.4 microM. In contrast, at concentrations up to 100 microM, clomiphene failed to inhibit both the chloride current activated by cyclic AMP (I(Cl,cAMP)) and the anionic background current (I(AB)). At 10 microM, clomiphene blocked the voltage-gated fast sodium current and the L-type calcium current (I(Ca,L)) in both species. The voltage-independent fractional block of I(Ca,L) induced by clomiphene (10 microM) was approximately 82%, this concentration also inhibited the inwardly rectifying K(+) current with a fractional current block of approximately 26% at -90 mV. Fractional block of outward current at +70 mV in rat was approximately 25%, implying that delayed rectifying K(+) channels were also affected by clomiphene. We conclude that clomiphene shows selectivity for I(Cl,vol) over I(Cl,cAMP) and I(AB) and therefore represents a useful tool for studying chloride conductances in isolated ventricular myocytes with interfering currents blocked. However, due to its effects on cation conductances it would be of little value in this regard for other types of in vitro or in vivo experiments.