Sculponeatin A promotes the ETS1-SYVN1 interaction to induce SLC7A11/xCT-dependent ferroptosis in breast cancer.

BACKGROUND: E26 transformation specificity-1 (ETS1) is a transcription factor that is overexpressed in breast cancer (BC) and promotes tumor progression. Sculponeatin A (stA), a new diterpenoid extracted from Isodon sculponeatus, has no reported antitumor mechanism. PURPOSE: Here, we explored the antitumor activity of stA in BC and further clarified its mechanism. METHODS: Ferroptosis was detected by flow cytometric, glutathione, malondialdehyde, and iron determination assays. The effect of stA on the upstream signaling pathway of ferroptosis was detected by Western blot, gene expression, gene alterations and other approaches. The binding of stA and ETS1 was examined through a microscale thermophoresis assay and a drug affinity responsive target stability assay. An in vivo mouse model experiment was performed to evaluate the therapeutic and potential mechanism of stA. RESULTS: stA exhibits therapeutic potential in BC by inducing SLC7A11/xCT-dependent ferroptosis. stA decreases the expression of ETS1, which is responsible for xCT-dependent ferroptosis in BC. stA inhibits the transcriptional expression of xCT by directly binding to the ETS domain of the ETS1 protein. In addition, stA promotes proteasomal degradation of ETS1 by triggering ubiquitin ligase synoviolin 1 (SYVN1)-mediated ubiquitination. The K318 site of ETS1 mediates ubiquitination of ETS1 by SYVN1. In a mouse model, stA inhibits tumor growth without causing obvious toxicity. CONCLUSION: Taken together, the results confirm that stA promotes the ETS1-SYVN1 interaction to induce ferroptosis in BC mediated by ETS1 degradation. stA is expected to be used in research of candidate drugs for BC and drug design based on ETS1 degradation.

Recent progress in the biology and physiology of BMP-8a.

PURPOSE: BMP-8a is a member of bone morphogenetic proteins (BMPs) and plays a regulatory role in human growth and development as a transcription regulator. This review aims to summarize the current research on the impact and mechanism of BMP-8a in female and male reproduction, formation and eruption of teeth, bone and cartilage development, tissue differentiation, disease occurrence, progression and prognosis. METHODS: The phrases "BMP-8a," "BMPs," "regulator," "mechanism," "osteoblast," "cartilage," "cancer," "disease," and "inflammation" were searched in the PubMed database. The abstracts were evaluated, and a series of original publications and reviews were examined. RESULTS: According to the search, BMP-8a affects the development of the uterus by inhibiting luteinization and plays an important role in late spermatogenesis. It is highly expressed in osteogenesis and differentially expressed in chondrogenesis. Furthermore, BMP-8a has a significant impact on the occurrence, development and prognosis of various diseases. CONCLUSIONS: BMP-8a regulates important factors and pathways, such as SMAD2/3 and SMAD1/5/8, to promote or inhibit the developmental processes of human reproductive organs. BMP-8a is also a member of the BMP family of proteins that regulates chondrogenesis and osteogenesis. In addition to its osteoinductive capabilities, BMP-8a is involved in the progression of diverse cancers.

[Ethoxysanguinarine directly targets CIP2A to inhibit proliferation and induce autophagy of SGC7901/DDP cells].

This study aims to investigate the effect of ethoxysanguinarine(Eth) on cisplatin(DDP)-resistant human gastric cancer cells and decipher the underlying mechanism. The human gastric cancer cell line SGC7901 and the DDP-resistant cell line SGC7901/DDP were used as the cell models. Western blot was employed to determine the expression levels of multidrug resistance-related proteins, and methyl thiazolyl tetrazolium(MTT) assay to detect the proliferation of SGC7901 and SGC7901/DDP cells exposed to DDP. After treatment with different concentrations of Eth, the proliferation of SGC7901 and SGC7901/DDP cells was detected by MTT assay, trypan blue exclusion assay, colony formation assay, and high-content imaging and analysis system. The apoptosis of SGC7901/DDP cells was detected by flow cytometry with Annexin V-FITC/PI staining. GFP-LC3 transfection was carried out to detect the effect of Eth on the autophagy of SGC7901/DDP cells. The expression levels of the multidrug resistance-related protein P-glycoprotein(P-gp), the apoptosis-related proteins [caspase-9, caspase-3, and poly(ADP-ribose) polymerase(PARP)], the autophagy-related protein light chain 3-Ⅱ(LC3-Ⅱ), the key effectors [mammalian target of rapamycin(mTOR), 70 kDa ribosomal protein S6 kinase(P70 S6 K), and 4 E binding protein 1(4 E-BP1)] of the mammalian target of rapamycin complex 1(mTORC1) signaling pathway, cancerous inhibitor of protein phosphatase 2A(CIP2A), and protein kinase B(Akt) were measured by Western blot. The mRNA level of CIP2A in the SGC7901/DDP cells exposed to Eth for 24 h was analyzed by RT-qPCR. After SGC7901/DDP cells were transfected with CIP2A expression vector pcDNA3.1-HA-CIP2A and treated with different concentrations of Eth, MTT assay was used to determine the prolife-ration of SGC7901/DDP cells and Western blot to detect the expression levels of related proteins. The interaction sites of Eth and CIP2A were predicted by molecular docking. The affinity between Eth and CIP2A was determined by drug affinity responsive target stability(DARTS) assay. The pharmacokinetic properties and drug-like activity of Eth were predicted by SwissADME. The results indicated that SGC7901/DDP cells were more sensitive to Eth than SGC7901 cells. Eth significantly inhibited proliferation and colony formation and changed the morphology, roundness, and area of SGC7901/DDP cells. Eth treatment caused the nucleus shrinking and significantly increased the apoptosis rate of the cells. Furthermore, Eth down-regulated the expression of caspase-9 and caspase-3 precursors and promoted the cleavage of PARP, which suggested that Eth induced the apoptosis of SGC7901/DDP cells. The GFP-LC3 in Eth-treated cells showed speckled aggregation. The up-regulated expression of LC3-Ⅱ by Eth indicated that Eth activated the autophagy of SGC7901/DDP cells. Eth down-regulated the expression of P-gp, the phosphorylation of mTOR, P70 S6K, and 4E-BP1, the expression of CIP2A, and the phosphorylation of Akt. Additionally, it increased the activity of PP2A, and had no significant effect on the expression of CIP2A in SGC7901/DDP cells. CIP2A overexpression antagonized the inhibition of cell proliferation and the activation of autophagy by Eth. Molecular docking suggested that Eth bound to CIP2A. The results of DARTS assay further proved the above binding effect. Eth has potential drug-like activity. The above results demonstrated that Eth inhibited the proliferation, induced the apoptosis, and activated the autophagy of SGC7901/DDP cells by targeting CIP2A and then down-regulating PP2A/mTORC1 signaling pathway. This study provided a new target for the treatment of cisplatin-resistant gastric cancer.

Involvement of Hepcidin in Cognitive Damage Induced by Chronic Intermittent Hypoxia in Mice.

Obstructive sleep apnea (OSA) patients exhibit different degrees of cognitive impairment, which is related to the activation of reactive oxygen species (ROS) production by chronic intermittent hypoxia (CIH) and the deposition of iron in the brain. As a central regulator of iron homeostasis, whether hepcidin is involved in OSA-induced cognitive impairment has not been clarified. In order to simulate OSA, we established the mouse model by reducing the percentage of inspired O2 (FiO2) from 21% to 5%, 20 times/h for 8 h/day. We found hepcidin was rising during CIH, along with increasing iron levels and neuron loss. Then, we constructed a mouse with astrocyte-specific knockdown hepcidin gene (shHamp). During CIH exposure, the shHamp mice showed a lower level of total iron and neuronal iron in the hippocampus, via stabilizing ferroportin 1 (FPN1) and decreasing L-ferritin (FTL) levels, when compared with wild-type (WT) mice. Furthermore, the shHamp mice showed a decrease of ROS by downregulating the elevated NADPH oxidase (NOX2) and 4-hydroxynonenal (4-HNE) levels mediated by CIH. In addition, the shHamp mice presented improved cognitive deficit by improving synaptic plasticity and BDNF expression in the hippocampus when subjected to CIH. Therefore, our data revealed that highly expressed hepcidin might promote the degradation of FPN1, resulting in neuronal iron deposition, oxidative stress damage, reduced synaptic plasticity, and impaired cognitive performance during CIH exposure.

Detection and recognition of ultrasound breast nodules based on semi-supervised deep learning: a powerful alternative strategy.

BACKGROUND: The successful recognition of benign and malignant breast nodules using ultrasound images is based mainly on supervised learning that requires a large number of labeled images. However, because high-quality labeling is expensive and time-consuming, we hypothesized that semi-supervised learning could provide a low-cost and powerful alternative approach. This study aimed to develop an accurate semi-supervised recognition method and compared its performance with supervised methods and sonographers. METHODS: The faster region-based convolutional neural network was used for nodule detection from ultrasound images. A semi-supervised classifier based on the mean teacher model was proposed to recognize benign and malignant nodule images. The general performance of the proposed method on two datasets (8,966 nodules) was reported. RESULTS: The detection accuracy was 0.88±0.03 and 0.86±0.02, respectively, on two testing sets (1,350 and 2,220 nodules). When 800 labeled training nodules were available, the proposed semi-supervised model plus 4,396 unlabeled nodules performed better than the supervised learning model (area under the curve (AUC): 0.934±0.026 vs. 0.83±0.050; 0.916±0.022 vs. 0.815±0.049). The performance of the semi-supervised model trained on 800 labeled and 4,396 unlabeled nodules was close to that of the supervised learning model trained on a massive number of labeled nodules (n=5,196) (AUC: 0.934±0.026 vs. 0.952±0.027; 0.916±0.022 vs. 0.918±0.017). Moreover, the semi-supervised model was better than the average accuracy of five human sonographers (AUC: 0.922 vs. 0.889). CONCLUSIONS: The semi-supervised model can achieve excellent performance for nodule recognition and be useful for medical sciences. The method reduced the number of labeled images required for training, thus significantly alleviating the difficulty in data preparation of medical artificial intelligence.

The efficacy and safety of high-dose tranexamic acid in adolescent idiopathic scoliosis: a meta-analysis.

BACKGROUND: This study aimed to evaluate the efficacy and safety of using high-dose intravenous tranexamic acid (TXA) to reduce blood loss in idiopathic scoliosis surgery. METHODS: This study was a meta-analysis, which consisted of retrospective cohort studies (RCSs) and randomized control trials (RCTs) found by searching electronic databases, namely PubMed, Web of Science, The Cochrane Central Register of Controlled Trials (CENTRAL), and the Google Scholar Database, dating from 1960 to 2019. The points of interest included total blood loss, a need for transfusion and transfusion criteria, surgery time, and the evidence of intraoperative and postoperative complications, such as seizures or thromboembolic events. The weighted mean differences (WMD) and 95% confidence interval (CI) of blood loss in the TXA intervention group compared to the control or placebo group were extracted and combined using the random effects model. RESULTS: In this meta-analysis, there was a total of three RCSs and two RCTs, which involved 334 patients. The results showed that blood loss is significantly reduced, with a weighted mean difference in the TXA group (WMD = - 525.14, P = 0.0000, CI ranged from - 839.83, - 210.44, I2 = 82%). Heterogeneity was assessed using the random effects model. CONCLUSIONS: A high dose of intravenous TXA reduced blood loss during adolescent idiopathic scoliosis surgery and did not lead to any significant thromboembolic event. Therefore, a high dose appears to be effective and safe for adolescent idiopathic scoliosis surgery. However, more high-quality research based on larger randomized controlled trials is still needed.

Huperzine A, reduces brain iron overload and alleviates cognitive deficit in mice exposed to chronic intermittent hypoxia.

Chronic intermittent hypoxia (CIH) is a consequence of obstructive sleep apnea (OSA), which increases reactive oxygen species (ROS) generation, resulting in oxidative damage and neurocognitive impairment. This study was designed to determine whether abnormal iron metabolism occurs in the brain under conditions of CIH and whether Huperzine A (HuA) could improve abnormal iron metabolism and neurological damage. The mouse model of CIH was established by reducing the percentage of inspired O2 (FiO2) from 21% to 9% 20 times/h for 8 h/day, and Huperzine A (HuA, 0.1 mg/kg, i.p.) was administered during CIH exposure for 21 days. HuA significantly improved cognitive impairment and neuronal damage in the hippocampus of CIH mice via increasing the ratio of Bcl-2/Bax and inhibiting caspase-3 cleavage. HuA considerably decreased ROS levels by downregulating the high levels of NADPH oxidase (NOX 2, NOX 4) mediated by CIH. There was an overload of iron, which was characterized by high levels of ferritin (FTL and FTH) and transferrin receptor 1 (TfR1) and low levels of ferroportin 1 (FPN1) in the hippocampus of CIH mice. Decreased levels of TfR1 and FTL proteins observed in HuA treated CIH group, could reduce iron overload in hippocampus. HuA increased PSD 95 protein expression, CREB activation and BDNF protein expression to protect against synaptic plasticity impairment induced by CIH. HuA acts as an effective iron chelator to attenuate apoptosis, oxidative stress and synaptic plasticity mediated by CIH.

Evidence that behavioral phenotypes of morphine in ß-arr2-/- mice are due to the unmasking of JNK signaling.

The altered behavioral effects of morphine, but not most other mu agonists, in mice lacking ß-arrestin 2, suggest that this scaffolding protein regulates the signaling cascade of this commonly used analgesic. One of the cascades that could be regulated by ß-arrestin 2 is cJun-N-terminal kinase (JNK), which binds with ß-arrestin 2 and modulates the analgesic effects of morphine. Using neurons lacking ß-arrestin 2 (ß-arr2-/-) to examine this interaction, we found that ß-arr2-/- neurons show altered intracellular distribution of JNK and cJun, and that morphine, but not fentanyl, increased the nuclear localization of the phosphorylated, therefore activated, form of cJun, a JNK target in dorsal root ganglia neurons. This suggests that deleting ß-arrestin 2 affects the JNK cascade. We therefore examined whether some of the behavioral phenotypes of mice lacking ß-arrestin 2 could be a result of altered JNK signaling. Indeed, two different JNK inhibitors reversed the enhanced analgesic effect of morphine, a known phenotype of ß-arr2-/- mice, to +/+ levels. Both the reduced locomotor effect of morphine and the psychomotor sensitization to repeated morphine administration in ß-arr2-/- mice were also returned to +/+ levels by inhibiting JNK. In contrast, the behavioral effects of fentanyl were neither genotype-dependent nor affected by JNK inhibition. Furthermore, a PKC inhibitor had a similar effect as inhibiting JNK in reducing the enhanced analgesic effect of morphine in ß-arr2-/- mice to +/+ levels. In summary, removing ß-arrestin 2 reveals mu receptor activation of the JNK cascade in a ligand-specific manner explaining several behavioral phenotypes of ß-arr2-/- mice.

Fighting fire with fire: poisonous Chinese herbal medicine for cancer therapy.

ETHNOPHARMACOLOGICAL RELEVANCE: Following the known principle of "fighting fire with fire", poisonous Chinese herbal medicine (PCHM) has been historically used in cancer therapies by skilled Chinese practitioners for thousands of years. In fact, most of the marketed natural anti-cancer compounds (e.g., camptothecin derivatives, vinca alkaloids, etc.) are often known in traditional Chinese medicine (TCM) and recorded as poisonous herbs as well. Inspired by the encouraging precedents, significant researches into the potential of novel anticancer drugs from other PCHM-derived natural products have been ongoing for several years and PCHM is increasingly being recognized as a gathering place for promising anti-cancer drugs. The present review aimed at giving a rational understanding of the toxicity of PCHM and, especially, providing the most recent developments on PCHM-derived anti-cancer compounds. MATERIALS AND METHODS: Information on the toxicity and safety control of PCHM, as well as PCHM-derived anti-cancer compounds, was gathered from the articles, books and monographs published in the past 20 years. RESULTS: Based on an objective introduction to the CHM toxicity, we clarified the general misconceptions about the safety of CHM and summarized the traditional experiences in dealing with the toxicity. Several PCHM-derived compounds, namely gambogic acid, triptolide, arsenic trioxide, and cantharidin, were selected as representatives, and their traditional usage and mechanism of anti-cancer actions were discussed. CONCLUSIONS: Natural products derived from PCHM are of extreme importance in devising new drugs and providing unique ideas for the war against cancer. To fully exploit the potential of PCHM in cancer therapy, more attentions are advocated to be focused on their safety evaluation and mechanism exploration.

Applications of nanoparticles in herbal medicine: zedoary turmeric oil and its active compound ß-elemene.

Zedoary turmeric oil and its main active ingredient ß-elemene are novel plant-derived anticancer agents with long-term clinical application history and low toxicity, which have been approved by the Chinese SFDA to treat different tumors including cancers of the brain, ovary, prostate, breast, lungs, liver, colon, and other tissues. Unfortunately, their hydrophobic properties, poor stabilities and low bioavailabilities seriously hamper their applications in clinic. Therefore, more attention should be paid to develop novel drug delivery systems for zedoary turmeric oil and ß-elemene to enhance their overall quality. Recently, increased research has been carried out on a nanoparticle drug delivery system of zedoary turmeric oil and ß-elemene to solve their poor aqueous solubilities and low bioavailabilities in vivo with much remarkable achievements springing up in the last decade. This review presents the novel nanoparticle formulations of zedoary turmeric oil and ß-elemene and introduces the possible future prospects of their further study.

U-shaped dose-dependent effects of BmK AS, a unique scorpion polypeptide toxin, on voltage-gated sodium channels.

BACKGROUND AND PURPOSE: Buthus martensi Karsch (BmK) AS is a scorpion polypeptide toxin, said to target the voltage-gated sodium channels (VGSCs). However, the mechanism of action of BmK AS on the VGSCs has yet to be defined. EXPERIMENTAL APPROACH: We examined the electrophysiological effects of BmK AS in a wide dose range on the rat brain-type VGSC alpha-subunit, rNav1.2a, heterologously expressed in Xenopus oocytes and on the VGSCs endogenously expressed in the dorsal root ganglion neuroblastoma ND7-23 cell line. KEY RESULTS: In the oocytes, BmK AS depolarized the voltage dependence of activation and inactivation of rNav1.2a at 0.1 and 500 nM whereas these parameters were hyperpolarized at 1 nM. In ND7-23 cells, BmK AS hyperpolarized the voltage dependence of activation and inactivation at 0.1, 1 and 100 nM but not 10 nM. BmK AS also hyperpolarized the voltage dependence of recovery from inactivation at 0.1 and 100 nM and slowed the recovery kinetics at all concentrations, but the effects of 1 and 10 nM were relatively smaller than those at 0.1 and 100 nM. Moreover, the inactivation of VGSCs was potentiated by 10 nM BmK AS in both systems, whereas it was inhibited by 0.1 or 100 nM BmK AS in the oocytes or ND7-23 cells respectively. CONCLUSIONS AND IMPLICATIONS: BmK AS modulated the VGSCs in a unique U-shaped dose-dependent manner, which could be due to the opposing effects of binding to two distinct receptor sites on the VGSCs.

C-terminal peptides coassemble into Abeta42 oligomers and protect neurons against Abeta42-induced neurotoxicity.

Alzheimer's disease (AD) is an age-related disorder that threatens to become an epidemic as the world population ages. Neurotoxic oligomers of Abeta42 are believed to be the main cause of AD; therefore, disruption of Abeta oligomerization is a promising approach for developing therapeutics for AD. Formation of Abeta42 oligomers is mediated by intermolecular interactions in which the C terminus plays a central role. We hypothesized that peptides derived from the C terminus of Abeta42 may get incorporated into oligomers of Abeta42, disrupt their structure, and thereby inhibit their toxicity. We tested this hypothesis using Abeta fragments with the general formula Abeta(x-42) (x = 28-39). A cell viability screen identified Abeta(31-42) as the most potent inhibitor. In addition, the shortest peptide, Abeta(39-42), also had high activity. Both Abeta(31-42) and Abeta(39-42) inhibited Abeta-induced cell death and rescued disruption of synaptic activity by Abeta42 oligomers at micromolar concentrations. Biophysical characterization indicated that the action of these peptides likely involved stabilization of Abeta42 in nontoxic oligomers. Computer simulations suggested a mechanism by which the fragments coassembled with Abeta42 to form heterooligomers. Thus, Abeta(31-42) and Abeta(39-42) are leads for obtaining mechanism-based drugs for treatment of AD using a systematic structure-activity approach.

Effects of BmK AS on Nav1.2 expressed in Xenopus laevis oocytes.

In the present study, the pharmacological effects of BmK AS, a beta-like scorpion toxin on rNav1.2 alpha-subunit expressed in Xenopus laevis oocytes were investigated using a two-electrode voltage-clamp recording. It was found that the voltage dependence of rNav1.2 inactivation was significantly shifted towards positive membrane potential by 500 nM BmK AS, whereas the activation curves of rNav1.2 were unruffled at the same dosage. The inactivation curves of both slow and fast inactivation currents were positively moved about 12.8 and 9.7 mV, respectively. In addition, the persistent currents of rNav1.2 were invariable. The effects of BmK AS on the rNav1.2 inactivation were opposite to the previous results found in the peripheral sensory neurons. The results suggested that Nav1.2 might be the target of BmK AS in the central nervous system, and BmK AS might have an excitatory effect on the central neuron through enhancing Nav1.2.

Chinese-scorpion (Buthus martensi Karsch) toxin BmK alphaIV, a novel modulator of sodium channels: from genomic organization to functional analysis.

In the present study, BmK alphaIV, a novel modulator of sodium channels, was cloned from venomous glands of the Chinese scorpion (Buthus martensi Karsch) and expressed successfully in Escherichia coli. The BmK alphaIV gene is composed of two exons separated by a 503 bp intron. The mature polypeptide contains 66 amino acids. BmK alphaIV has potent toxicity in mice and cockroaches. Surface-plasmon-resonance analysis found that BmK alphaIV could bind to both rat cerebrocortical synaptosomes and cockroach neuronal membranes, and shared similar binding sites on sodium channels with classical AaH II (alpha-mammal neurotoxin from the scorpion Androctonus australis Hector), BmK AS (beta-like neurotoxin), BmK IT2 (the depressant insect-selective neurotoxin) and BmK abT (transitional neurotoxin), but not with BmK I (alpha-like neurotoxin). Two-electrode voltage clamp recordings on rNav1.2 channels expressed in Xenopus laevis oocytes revealed that BmK alphaIV increased the peak amplitude and prolonged the inactivation phase of Na+ currents. The structural and pharmacological properties compared with those of other scorpion alpha-toxins suggests that BmK alphaIV represents a novel subgroup or functional hybrid of alpha-toxins and might be an evolutionary intermediate neurotoxin for alpha-toxins.

Phosphoinositide 3-kinase cascade facilitates mu-opioid desensitization in sensory neurons by altering G-protein-effector interactions.

Signaling via G-protein-coupled receptors undergoes desensitization after prolonged agonist exposure. Here we investigated the role of phosphoinositide 3-kinase (PI3K) and its downstream pathways in desensitization of micro-opioid inhibition of neuronal Ca2+ channels. In cultured mouse dorsal root ganglion neurons, two mechanistically different forms of desensitization were observed after acute or chronic treatment with the micro agonist [D-Ala2, N-MePhe4, Gly-ol5]-enkephalin (DAMGO). Chronic DAMGO desensitization was heterologous in nature and significantly attenuated by blocking the activity of PI3K or mitogen-activated protein kinase (MAPK). A combined application of PI3K and MAPK inhibitors showed no additive effect, suggesting that these two kinases act in a common pathway to facilitate chronic desensitization. Acute DAMGO desensitization, however, was not affected by the inhibitors. Furthermore, upregulation of the PI3K-Akt pathway in mutant mice lacking phosphatase and tensin homolog, a lipid phosphatase counteracting PI3K, selectively enhanced chronic desensitization in a PI3K- and MAPK-dependent manner. Using the prepulse facilitation (PPF) test, we further examined changes in the voltage-dependent component of DAMGO action that requires direct interactions between betagamma subunits of G-proteins and Ca2+ channels. DAMGO-induced PPF was diminished after chronic treatment, suggesting disruption of G-protein-channel interactions. Such disruption could occur at the postreceptor level, because chronic DAMGO also reduced GTPgammaS-induced PPF that was independent of receptor activation. Again, inhibition of PI3K or MAPK reduced desensitization of PPF. Our data suggest that the PI3Kcascade involving MAPK and Akt enhances micro-opioid desensitization via postreceptor modifications that interfere with G-protein-effector interactions.

Modulation of the human polycystin-L channel by voltage and divalent cations.

Polycystin-L (PCL) is highly homologous in sequence and membrane topology to polycystin-2, the product of the second gene responsible for autosomal dominant polycystic kidney disease (ADPKD). PCL and polycystin-2 were recently shown to be Ca2+-permeable, Ca2+-activated cation channels. Further characterization of polycystins will help in the understanding of cystogenesis and pathogenesis of ADPKD. In the present study, we expressed human PCL in Xenopus oocytes and studied its function utilizing patch-clamp and two-electrode voltage clamp techniques. In addition to its permeability to Ca2+, K+ and Na+, PCL was highly permeable to NH4+ and Cs+ with a permeability ratio NH4+:Cs+:Na+ of 2.2:1.02:1. Voltage modulation of channel properties was studied using cell-attached (C-A) and excised inside-out (I-O) patches. In the C-A mode, the open probability (NP(o)) of PCL at negative potentials (NP(o)=0.22) was higher than at positive potentials (NP(o)=0.05). The mean open time averaged 31.6 ms at negative potentials, and 6.2 ms at positive potentials; single-channel activity exhibited bursts with a mean interburst time of 178 ms. Using I-O patches under symmetrical ionic conditions, single-channel inward conductance was significantly larger than outward conductance, indicating a slight inward rectification. External Mg2+ inhibited the PCL channel currents. The inhibitory effect was voltage-dependent and substantially reduced by depolarization. The time course of inactivation depended on external calcium concentration but was independent of voltage and peak current. This study shows that although PCL is not a voltage-gated channel, its channel activity and inhibition by Mg2+ are modulated by membrane potential.