Nodulisporic acid produces direct activation and positive allosteric modulation of AVR-14B, a glutamate-gated chloride channel from adult Brugia malayi.

Glutamate-gated chloride channels (GluCls) are unique to invertebrates and are targeted by macrocyclic lactones. In this study, we cloned an AVR-14B GluCl subunit from adult Brugia malayi, a causative agent of lymphatic filariasis in humans. To elucidate this channel's pharmacological properties, we used Xenopus laevis oocytes for expression and performed two-electrode voltage-clamp electrophysiology. The receptor was gated by the natural ligand L-glutamate (effective concentration, 50% [EC50] = 0.4 mM) and ivermectin (IVM; EC50 = 1.8 nM). We also characterized the effects of nodulisporic acid (NA) on Bma-AVR-14B and NA-produced dual effects on the receptor as an agonist and a type II positive allosteric modulator. Here we report characterization of the complex activity of NA on a nematode GluCl. Bma-AVR-14B demonstrated some unique pharmacological characteristics. IVM did not produce potentiation of L-glutamate-mediated responses but instead, reduced the channel's sensitivity for the ligand. Further electrophysiological exploration showed that IVM (at a moderate concentration of 0.1 nM) functioned as an inhibitor of both agonist and positive allosteric modulatory effects of NA. This suggests that IVM and NA share a complex interaction. The pharmacological properties of Bma-AVR-14B indicate that the channel is an important target of IVM and NA. In addition, the unique electrophysiological characteristics of Bma-AVR-14B could explain the observed variation in drug sensitivities of various nematode parasites. We have also shown the inhibitory effects of IVM and NA on adult worm motility using Worminator. RNA interference (RNAi) knockdown suggests that AVR-14 plays a role in influencing locomotion in B. malayi.

Chloride transport modulators as drug candidates.

Chloride transport across cell membranes is broadly involved in epithelial fluid transport, cell volume and pH regulation, muscle contraction, membrane excitability, and organellar acidification. The human genome encodes at least 53 chloride-transporting proteins with expression in cell plasma or intracellular membranes, which include chloride channels, exchangers, and cotransporters, some having broad anion specificity. Loss-of-function mutations in chloride transporters cause a wide variety of human diseases, including cystic fibrosis, secretory diarrhea, kidney stones, salt-wasting nephropathy, myotonia, osteopetrosis, hearing loss, and goiter. Although impactful advances have been made in the past decade in drug treatment of cystic fibrosis using small molecule modulators of the defective cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel, other chloride channels and solute carrier proteins (SLCs) represent relatively underexplored target classes for drug discovery. New opportunities have emerged for the development of chloride transport modulators as potential therapeutics for secretory diarrheas, constipation, dry eye disorders, kidney stones, polycystic kidney disease, hypertension, and osteoporosis. Approaches to chloride transport-targeted drug discovery are reviewed herein, with focus on chloride channel and exchanger classes in which recent preclinical advances have been made in the identification of small molecule modulators and in proof of concept testing in experimental animal models.

ClC-3: A Novel Promising Therapeutic Target for Atherosclerosis.

Chloride channel 3 (ClC-3), a Cl-/H+ antiporter, has been well established as a member of volume-regulated chloride channels (VRCCs). ClC-3 may be a crucial mediator for activating inflammation-associated signaling pathways by regulating protein phosphorylation. A growing number of studies have indicated that ClC-3 overexpression plays a crucial role in mediating increased plasma low-density lipoprotein levels, vascular endothelium dysfunction, pro-inflammatory activation of macrophages, hyper-proliferation and hyper-migration of vascular smooth muscle cells (VSMCs), as well as oxidative stress and foam cell formation, which are the main factors responsible for atherosclerotic plaque formation in the arterial wall. In the present review, we summarize the molecular structures and classical functions of ClC-3. We further discuss its emerging role in the atherosclerotic process. In conclusion, we explore the potential role of ClC-3 as a therapeutic target for atherosclerosis.

Antiviral Drug Ivermectin at Nanomolar Concentrations Inhibits Glycine-Induced Chloride Current in Rat Hippocampal Neurons.

Ivermectin (IVM) belongs to the class of macrocyclic lactones, which is used as an antiparasitic agent. At present, the researchers focus on possibility to use IVM in treatment of certain forms of cancer and viral diseases such as COVID-19. The mechanisms of IVM action are not clear. It is assumed that IVM affects chloride channels and increases cytoplasmic concentration of chloride. This study examines the effect of IVM on chloride currents induced by glycine (IGly). Experiments were carried out on isolated pyramidal neurons of the rat hippocampus with whole-cell patch clamp. A short-term (600 msec) application of IVM in a concentration of 10 µM induced a slow inward current, which persisted after washing the neurons. The low concentrations (0.1-1000 nM) of IVM did not induce any novel current, but it rapidly and reversibly reduced the peak amplitude and accelerated desensitization of IGly in a dose-dependent manner. The threshold concentrations of IVM sufficient to reduce peak amplitude of IGly and to accelerate desensitization of IGly were 100 nM and 0.1 nM, respectively. The study revealed a high sensitivity of neuronal glycine receptors to IVM.

Two novel loci underlie natural differences in Caenorhabditis elegans abamectin responses.

Parasitic nematodes cause a massive worldwide burden on human health along with a loss of livestock and agriculture productivity. Anthelmintics have been widely successful in treating parasitic nematodes. However, resistance is increasing, and little is known about the molecular and genetic causes of resistance for most of these drugs. The free-living roundworm Caenorhabditis elegans provides a tractable model to identify genes that underlie resistance. Unlike parasitic nematodes, C. elegans is easy to maintain in the laboratory, has a complete and well annotated genome, and has many genetic tools. Using a combination of wild isolates and a panel of recombinant inbred lines constructed from crosses of two genetically and phenotypically divergent strains, we identified three genomic regions on chromosome V that underlie natural differences in response to the macrocyclic lactone (ML) abamectin. One locus was identified previously and encodes an alpha subunit of a glutamate-gated chloride channel (glc-1). Here, we validate and narrow two novel loci using near-isogenic lines. Additionally, we generate a list of prioritized candidate genes identified in C. elegans and in the parasite Haemonchus contortus by comparison of ML resistance loci. These genes could represent previously unidentified resistance genes shared across nematode species and should be evaluated in the future. Our work highlights the advantages of using C. elegans as a model to better understand ML resistance in parasitic nematodes.

Ivermectin: An Anthelmintic, an Insecticide, and Much More.

Here we tell the story of ivermectin, describing its anthelmintic and insecticidal actions and recent studies that have sought to reposition ivermectin for the treatment of other diseases that are not caused by helminth and insect parasites. The standard theory of its anthelmintic and insecticidal mode of action is that it is a selective positive allosteric modulator of glutamate-gated chloride channels found in nematodes and insects. At higher concentrations, ivermectin also acts as an allosteric modulator of ion channels found in host central nervous systems. In addition, in tissue culture, at concentrations higher than anthelmintic concentrations, ivermectin shows antiviral, antimalarial, antimetabolic, and anticancer effects. Caution is required before extrapolating from these preliminary repositioning experiments to clinical use, particularly for Covid-19 treatment, because of the high concentrations of ivermectin used in tissue-culture experiments.

G551D mutation impairs PKA-dependent activation of CFTR channel that can be restored by novel GOF mutations.

G551D is a major disease-associated gating mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) protein, an ATP- and phosphorylation-dependent chloride channel. G551D causes severe cystic fibrosis (CF) disease by disrupting ATP-dependent channel opening; however, whether G551D affects phosphorylation-dependent channel activation is unclear. Here, we use macropatch recording and Ussing chamber approaches to demonstrate that G551D impacts on phosphorylation-dependent activation of CFTR, and PKA-mediated phosphorylation regulates the interaction between the x-loop in nucleotide-binding domain 2 (NBD2) and cytosolic loop (CL) 1. We show that G551D not only disrupts ATP-dependent channel opening but also impairs phosphorylation-dependent channel activation by largely reducing PKA sensitivity consistent with the reciprocal relationship between channel opening/gating, ligand binding, and phosphorylation. Furthermore, we identified two novel GOF mutations: D1341R in the x-loop near the ATP-binding cassette signature motif in NBD2 and D173R in CL1, each of which strongly increased PKA sensitivity both in the wild-type (WT) background and when introduced into G551D-CFTR. When D1341R was combined with a second GOF mutation (e.g., K978C in CL3), we find that the double GOF mutation maximally increased G551D channel activity such that VX-770 had no further effect. We further show that a double charge-reversal mutation of D1341R/D173R-CFTR exhibited similar PKA sensitivity when compared with WT-CFTR. Together, our results suggest that charge repulsion between D173 and D1341 of WT-CFTR normally inhibits channel activation at low PKA activity by reducing PKA sensitivity, and negative allostery by the G551D is coupled to reduced PKA sensitivity of CFTR that can be restored by second GOF mutations.

Short Chain Fatty Acids Effect on Chloride Channel ClC-2 as a Possible Mechanism for Lubiprostone Intestinal Action.

Lubiprostone, a 20-carbon synthetic fatty acid used for the treatment of constipation, is thought to act through an action on Cl- channel ClC-2. Short chain fatty acids (SCFAs) are produced and absorbed in the distal intestine. We explore whether SCFAs affect ClC-2, re-examine a possible direct effect of lubiprostone on ClC-2, and use mice deficient in ClC-2 to stringently address the hypothesis that the epithelial effect of lubiprostone targets this anion channel. Patch-clamp whole cell recordings of ClC-2 expressed in mammalian cells are used to assay SCFA and lubiprostone effects. Using chamber measurements of ion current in mice deficient in ClC-2 or CFTR channels served to analyze the target of lubiprostone in the distal intestinal epithelium. Intracellular SCFAs had a dual action on ClC-2, partially inhibiting conduction but, importantly, facilitating the voltage activation of ClC-2. Intra- or extracellular lubiprostone had no effect on ClC-2 currents. Lubiprostone elicited a secretory current across colonic epithelia that was increased in mice deficient in ClC-2, consistent with the channel's proposed proabsorptive function, but absent from those deficient in CFTR. Whilst SCFAs might exert a physiological effect on ClC-2 as part of their known proabsorptive effect, ClC-2 plays no part in the lubiprostone intestinal effect that appears mediated by CFTR activation.

Regulation of Cl- Electrolyte Permeability in Epithelia by Active Traditional Chinese Medicine Monomers for Diarrhea.

The epithelial layer, lining the inner surface of the mammalian alveolar, kidney, brain and colon, is a typical electrolyte transporting tissue. Large quantities of salt and fluid are actively moved from the mucosal side toward the blood vessel. Transepithelial salt re-absorption in epithelial tissues plays an important role in maintaining fluid homeostasis. In absorptive epithelium, fluid and salt flux is controlled by the machinery mainly composed of epithelial sodium channel, cystic fibrosis transmembrane conductance regulator, Na+-K+-2Cl- cotransporter, Na+/H+ exchanger, and Na+/K+-ATPase. Dysregulation of salt permeability across epithelium contributes to the pathogenesis of organ edema. In numerous ion transporters, epithelial Cl- transportation plays an important role in water secretion across epithelial tissues and regulation of body fluid content. Many traditional Chinese medicines treat diarrhea by regulating the Cl- electrolyte transport. We systematically summarized the recent progress regarding the traditional Chinese medicine on Cl- electrolyte transport in the intestinal epithelial tissues. The pharmaceutical relevance of developing advanced strategies to mitigate edematous disorders is also implicated. In conclusion, the crosstalk between Cl- electrolyte transport and active traditional Chinese medicine monomers may lead to the development of new strategies for diarrhea by manipulating the function and expression of ion channels.

PAC proton-activated chloride channel contributes to acid-induced cell death in primary rat cortical neurons.

Severe local acidosis causes tissue damage and pain, and is associated with many diseases, including cerebral and cardiac ischemia, cancer, infection, and inflammation. However, the molecular mechanisms of the cellular response to extracellular acidic environment are not fully understood. We recently identified a novel and evolutionarily conserved membrane protein, PAC (also known as PACC1 or TMEM206), encoding the proton-activated chloride (Cl-) channel, whose activity is widely observed in human cell lines. We demonstrated that genetic deletion of Pac abolished the proton-activated Cl- currents in mouse neurons and also attenuated the acid-induced neuronal cell death and brain damage after ischemic stroke. Here, we show that the proton-activated Cl- currents are also conserved in primary rat cortical neurons, with characteristics similar to those observed in human and mouse cells. Pac gene knockdown nearly abolished the proton-activated Cl- currents in rat neurons and reduced the neuronal cell death triggered by acid treatment. These data further support the notion that activation of the PAC channel and subsequent Cl- entry into neurons during acidosis play a pathogenic role in acidotoxicity and brain injury.

Nanomolar Potency Aminophenyltriazine CFTR Activator Reverses Corneal Epithelial Injury in a Mouse Model of Dry Eye.

Purpose: Dry eye disorders are a major health care burden. We previously reported the identification of N-methyl-N-phenyl-6-(2,2,3,3-tetrafluoropropoxy)-1,3,5-triazine-2,4-diamine [cystic fibrosis transmembrane conductance regulator (CFTR)act-K267], which activated human wild-type CFTR chloride conductance with EC50 ∼ 30 nM. Here, we report in vivo evidence for CFTRact-K267 efficacy in an experimental mouse model of dry eye using a human compatible ophthalmic vehicle. Methods: CFTR activation in mice in vivo was demonstrated by ocular surface potential difference (OSPD) measurements. Ocular surface pharmacodynamics was measured in tear fluid samples obtained at different times after topical administration of CFTRact-K267. Dry eye was produced by lacrimal duct cautery (LDC) and corneal epithelial injury and was assessed by Lissamine green (LG) staining. Results: OSPD measurements demonstrated a hyperpolarization of -8.6 ± 3 mV (standard error of the mean, 5 mice) in response to CFTRact-K267 exposure in low chloride solution that was reversed by a CFTR inhibitor. Following single-dose topical administration of 2 nmol CFTRact-K267, tear fluid CFTRact-K267 concentration was >500 nM for more than 6 h. Following LDC, corneal surface epithelial injury, as assessed by LG staining, was substantially reversed in 10 of 12 eyes receiving 2 nmol CFTRact-K267 3 times daily starting on day 2, when marked epithelial injury had already occurred. Improvement was seen in 3 of 12 vehicle-treated eyes. Conclusion: These studies provide in vivo evidence in mice for the efficacy of a topical, human use compatible CFTRact-K267 formulation in stimulating chloride secretion and reversing corneal epithelial injury in dry eye.

Insights into the impact of Ivermectin on some protein aspects linked to Culex pipiens digestion and immunity.

In developing countries, low-cost control and treatment programs that offer combined approaches against diseases and their vectors are certainly needed. Ivermectin (IVM) has been well known for its role in the treatment of parasitic diseases, due to its effect on glutamate-gated chloride channels. These same channels are also present in the mosquito vector, and thus, research has focused on the insecticidal effects of this drug. Possible alternative mechanisms of IVM on the physiology of mosquitoes, however, have not been sufficiently elaborated. We assessed the protease activity, lipid peroxidation, and local expression of STAT, p53, caspase-3, and Bax markers to study the effect of this antibiotic on digestion and immunity in Culex pipiens. Sugar- and blood-feeding assays were employed to investigate the potential influence of blood feeding on the dynamics of these parameters. IVM was found to have an effect on protease activity, lipid peroxidation as well as the expression of different markers investigated in this work. The focus on the detailed effect of this drug certainly opens the gate to broadening the spectrum of IVM and expanding its health and economic benefit, especially that it is relatively more affordable than other antibiotics on the market.

Extracellular pH and intracellular phosphatidylinositol 4,5-bisphosphate control Cl- currents in guinea pig detrusor smooth muscle cells.

Cl- channels serve as key regulators of excitability and contractility in vascular, intestinal, and airway smooth muscle cells. We recently reported a Cl- conductance in detrusor smooth muscle (DSM) cells. Here, we used the whole cell patch-clamp technique to further characterize biophysical properties and physiological regulators of the Cl- current in freshly isolated guinea pig DSM cells. The Cl- current demonstrated outward rectification arising from voltage-dependent gating of Cl- channels rather than the Cl- transmembrane gradient. An exposure of DSM cells to hypotonic extracellular solution (Δ 165 mOsm challenge) did not increase the Cl- current providing strong evidence that volume-regulated anion channels do not contribute to the Cl- current in DSM cells. The Cl- current was monotonically dependent on extracellular pH, larger and lower in magnitude at acidic (5.0) and basic pH (8.5) values, respectively. Additionally, intracellularly applied phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] analog [PI(4,5)P2-diC8] increased the average Cl- current density by approximately threefold in a voltage-independent manner. The magnitude of the DSM whole cell Cl- current did not depend on the cell surface area (cell capacitance) regardless of the presence or absence of PI(4,5)P2-diC8, an intriguing finding that underscores the complex nature of Cl- channel expression and function in DSM cells. Removal of both extracellular Ca2+ and Mg2+ did not affect the DSM whole cell Cl- current, whereas Gd3+ (1 mM) potentiated the current. Collectively, our recent and present findings strongly suggest that Cl- channels are critical regulators of DSM excitability and are regulated by extracellular pH, Gd3+, and PI(4,5)P2.

Molecular basis of PIP2-dependent regulation of the Ca2+-activated chloride channel TMEM16A.

The calcium-activated chloride channel (CaCC) TMEM16A plays crucial roles in regulating neuronal excitability, smooth muscle contraction, fluid secretion and gut motility. While opening of TMEM16A requires binding of intracellular Ca2+, prolonged Ca2+-dependent activation results in channel desensitization or rundown, the mechanism of which is unclear. Here we show that phosphatidylinositol (4,5)-bisphosphate (PIP2) regulates TMEM16A channel activation and desensitization via binding to a putative binding site at the cytosolic interface of transmembrane segments (TMs) 3-5. We further demonstrate that the ion-conducting pore of TMEM16A is constituted of two functionally distinct modules: a Ca2+-binding module formed by TMs 6-8 and a PIP2-binding regulatory module formed by TMs 3-5, which mediate channel activation and desensitization, respectively. PIP2 dissociation from the regulatory module results in ion-conducting pore collapse and subsequent channel desensitization. Our findings thus provide key insights into the mechanistic understanding of TMEM16 channel gating and lipid-dependent regulation.

Cell Volume-Activated and Volume-Correlated Anion Channels in Mammalian Cells: Their Biophysical, Molecular, and Pharmacological Properties.

There are a number of mammalian anion channel types associated with cell volume changes. These channel types are classified into two groups: volume-activated anion channels (VAACs) and volume-correlated anion channels (VCACs). VAACs can be directly activated by cell swelling and include the volume-sensitive outwardly rectifying anion channel (VSOR), which is also called the volume-regulated anion channel; the maxi-anion channel (MAC or Maxi-Cl); and the voltage-gated anion channel, chloride channel (ClC)-2. VCACs can be facultatively implicated in, although not directly activated by, cell volume changes and include the cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, the Ca2+-activated Cl- channel (CaCC), and the acid-sensitive (or acid-stimulated) outwardly rectifying anion channel. This article describes the phenotypical properties and activation mechanisms of both groups of anion channels, including accumulating pieces of information on the basis of recent molecular understanding. To that end, this review also highlights the molecular identities of both anion channel groups; in addition to the molecular identities of ClC-2 and CFTR, those of CaCC, VSOR, and Maxi-Cl were recently identified by applying genome-wide approaches. In the last section of this review, the most up-to-date information on the pharmacological properties of both anion channel groups, especially their half-maximal inhibitory concentrations (IC50 values) and voltage-dependent blocking, is summarized particularly from the standpoint of pharmacological distinctions among them. Future physiologic and pharmacological studies are definitely warranted for therapeutic targeting of dysfunction of VAACs and VCACs.

The Natural Compound Cinnamaldehyde is a Novel Activator of Calcium-Activated Chloride Channel.

Calcium-activated chloride channels (CaCCs) play important roles in a multitude of physiological processes, and in many cells types, TMEM16A was identified as the molecular basis of CaCC. Abnormal CaCC function has been implicated in variety of diseases, which reinforces the need for modulators of CaCCs/TMEM16A. However, there are few specific, clinical modulators of CaCCs. Here, we identified a potent novel activator of TMEM16A from a bank of traditional Chinese medicines (TCM) and explored its mechanism of activation by laser confocal scanning microscopy and patch clamping. Fluorescence data demonstrated that among the 36 tested TCM medicines, one compound, cinnamaldehyde (CA), can activate the TMEM16A channel in a dose-dependent manner. To determine the mechanism by which CA activates the TMEM16A channel, we performed an excised patch clamp experiment and measured the intracellular calcium concentration in fluorescence experiments. Our data show that CA activates TMEM16A channels by elevating the intracellular concentrations of calcium ions. The results of the whole-cell patch clamping showed that CA dose-dependently activates these channels, with an EC50 of 9.73 ± 5.64 µM at + 80 mV, and prolongs the deactivation of TMEM16A. Finally, we found that CA can strengthen contractions of the ileum in guinea pigs by activating TMEM16A. The results demonstrate that CA is a novel, natural activator of TMEM16A.

The fungal alkaloid Okaramine-B activates an L-glutamate-gated chloride channel from Ixodes scapularis, a tick vector of Lyme disease.

A novel L-glutamate-gated anion channel (IscaGluCl1) has been cloned from the black-legged tick, Ixodes scapularis, which transmits multiple pathogens including the agents of Lyme disease and human granulocytic anaplasmosis. When mRNA encoding IscaGluCl1 was expressed in Xenopus laevis oocytes, we detected robust 50-400 nA currents in response to 100 µM L-glutamate. Responses to L-glutamate were concentration-dependent (pEC50 3.64 ±â€¯0.11). Ibotenate was a partial agonist on IscaGluCl1. We detected no response to 100 µM aspartate, quisqualate, kainate, AMPA or NMDA. Ivermectin at 1 µM activated IscaGluCl1, whereas picrotoxinin (pIC50 6.20 ±â€¯0.04) and the phenylpyrazole fipronil (pIC50 6.90 ±â€¯0.04) showed concentration-dependent block of the L-glutamate response. The indole alkaloid okaramine B, isolated from fermentation products of Penicillium simplicissimum (strain AK40) grown on okara pulp, activated IscaGluCl1 in a concentration-dependent manner (pEC50 5.43 ±â€¯0.43) and may serve as a candidate lead compound for the development of new acaricides.

Biosynthesis and Structure-Activity Relationship Studies of Okaramines That Target Insect Glutamate-Gated Chloride Channels.

Prenylated indole alkaloid okaramines selectively target insect glutamate-gated chloride channels (GluCls). Because of their highly complex structures, including azocine and azetidine rings, total synthesis of okaramine A or B has not been achieved, preventing evaluation of the biological activities of okaramines. Biosynthetic approaches provide alternatives to accessing structurally diverse derivatives and enabling the elucidation of structure-activity relationships. To explore the biosynthetic potential of okaramines, gene knockout experiments of an okaramine-producer fungus were performed. The deletion mutants of the oxygenase genes okaB, okaD, okaE, and okaG provided analogues that were unlikely to be accumulated in the normal biosynthetic process of the wild-type strain. Analysis of the structure-activity relationships of okaramines collected from the fungal cultures revealed that 1,4-dihydroazocine and N-aliphatic group attached to the indole were crucial for GluCl-activating activity. This provided insights into further derivatization of the complex structure of okaramines in order to facilitate the development of new insecticides.

Molecular, biophysical, and pharmacological properties of calcium-activated chloride channels.

Calcium-activated chloride channels (CaCCs) are a family of anionic transmembrane ion channels. They are mainly responsible for the movement of Cl- and other anions across the biological membranes, and they are widely expressed in different tissues. Since the Cl- flow into or out of the cell plays a crucial role in hyperpolarizing or depolarizing the cells, respectively, the impact of intracellular Ca2+ concentration on these channels is attracting a lot of attentions. After summarizing the molecular, biophysical, and pharmacological properties of CaCCs, the role of CaCCs in normal cellular functions will be discussed, and I will emphasize how dysregulation of CaCCs in pathological conditions can account for different diseases. A better understanding of CaCCs and a pivotal regulatory role of Ca2+ can shed more light on the therapeutic strategies for different neurological disorders that arise from chloride dysregulation, such as asthma, cystic fibrosis, and neuropathic pain.

Activation of ClC-3 chloride channel by 17ß-estradiol relies on the estrogen receptor α expression in breast cancer.

Although extensively studied, the mechanisms by which estrogen promotes breast cancer growth remain to be fully elucidated. Tamoxifen, an antiestrogen agent to treat ERα+ breast cancer, is also a high-affinity blocker of the chloride channels. In this study, we explored the involvement of the chloride channels in the action of estrogen in breast cancer. We found that 17ß-estradiol (17ß-E2) concentration-dependently activated the chloride currents in ERα+ breast cancer MCF-7 cells. Extracellular hypertonic challenge and chloride channel blockers, NPPB and DIDS inhibited the 17ß-E2-activated chloride currents. Decreased the ClC-3 protein expression caused the depletion of the 17ß-E2-activated chloride currents. 17ß-E2-activated chloride currents which relied on the ERα expression were demonstrated by the following evidences. Firstly, 17ß-E2-activated chloride currents could not be observed in ERα- breast cancer MDA-MB-231 cells. Secondly, ER antagonists, tamoxifen and ICI 182,780, and downregulation of ERα expression inhibited or abolished the 17ß-E2-activated chloride currents. Thirdly, ERα expression was induced in MDA-MB-231 cells by ESR1 gene transfection, and then 17ß-E2-activated chloride currents could be observed. In MCF-7 cells, ERα and ClC-3 mainly located in nucleus and translocated to cell plasma and membrane with respect to co-localization following treatment of 17ß-E2. Downregulation of ERα expression could decrease the expression of ClC-3 protein. Conversely, downregulation of ClC-3 expression did not influence the ERα expression. Taken together, our findings demonstrated that ClC-3 is a potential target of 17ß-E2 and is modulated by the ERα in breast cancer cell. Pharmacological modulation of ClC-3 may provide a deep understanding in antiestrogen treatment of breast cancer patients.