APOBEC3B expression has prognostic significance in cervical cancer.

OBJECTIVE: Cervical cancer is one of the leading fatal diseases in women, and the role of Apolipoprotein B mRNA editing enzyme catalytic subunit 3B (APOBEC3B) in cervical cancer is uncertain. METHODS: Four Gene Expression Omnibus (GEO) mRNA microarray datasets were analyzed to identify differentially expressed genes (DEGs) between cervical cancer and normal cervical tissues. The results were validated using a The Cancer Genome Atlas (TCGA)-cervical cancer (CESC) dataset. Expression profiles and patients' clinical data were used to investigate the relationship between APOBEC3B expression and cervical cancer survival. APOBEC3B co-expressed genes were subjected to enrichment analyses, and correlations between APOBEC3B expression and immunologic infiltrates were investigated using Tumor Immune Estimation Resource (TIMER). We generated receiver operating characteristic curve (ROC) curves to evaluate the performance of APOBEC3B expression in predicting cervical cancer prognosis. RESULTS: Fourteen overlapping DEGs were obtained, and APOBEC3B was chosen as a candidate gene. TCGA data further confirmed that APOBEC3B was significantly increased in cervical cancer, relative to normal adjacent tissues, and this expression was associated with poor clinical outcome. Results from quantitative real time polymerase chain reaction (RT-qPCR) and immunohistochemical staining of cervical carcinoma tissues supported these findings. Enrichment analysis showed that APOBEC3B co-expressed genes were mainly enriched in cell cycle, DNA replication and chromosomal region. Moreover, APOBEC3B expression was significantly associated with T stage, M stage, primary therapy outcome and poor clinical prognosis in cervical cancer. Similarly, APOBEC3B was closely correlated with gene markers of diverse immune cells. APOBEC3B expression was an independent indicator of cervical cancer prognosis, according to univariate Cox and ROC analyses. CONCLUSION: High APOBEC3B expression is strongly related to a poor prognosis in cervical cancer patients.

Propionate alleviated post-infarction cardiac dysfunction by macrophage polarization in a rat model.

BACKGROUND: The propionate (C3), the important components of short-chain fatty acids (SCFAs), had the effect of inhibiting pro-inflammatory macrophages. Earlier macrophages phenotypic transition from pro-inflammatory M1 to reparative M2 in early stage was a central juncture of cardiac dysfunction mitigation after myocardial infarction (MI). METHODS: 160 Sprague-Dawley rats were assigned to 4 groups: sham group (n = 40), sham + C3 group (n = 40), MI group (n = 40) and MI + C3 group (n = 40). The rats in sham + C3 and MI + C3 group were treated with oral sodium propionate (200 mM), and equivalent concentration of sodium chloride was administered in sham and MI group as control. After 7 days of propionate adaptive feeding, rats were anesthetized and induced the MI by coronary occlusion. The classification of macrophages, the level of inflammatory factors and inflammatory signaling were estimated at 3rd days after thoracotomy, and the extent of myocardial fibrosis was evaluated at 7th and 28th days after operation. Echocardiography was estimated on 28th day after surgery. RAW264.7 cells, stimulated by LPS + IFN-γ with or without propionate, were harvested for western blot and supernatants were collected for cytokine analysis by ELISA. RESULTS: Propionate administration reduced the MI-induced myocardial fibrosis in infarcted border and attenuated cardiac function deterioration compared with MI group. In comparison with MI group, propionate promoted macrophages reduction, macrophage M2-like polarization, and inflammatory cytokines decrease in infarcted border zone following MI, which partly depends on the inhibition of JNK/P38/NFκB signaling pathways. CONCLUSIONS: Oral propionate in early stage, as a nutritional intervention, alleviated post-MI chronic cardiac remodeling and cardiac dysfunction at least in part by modulating macrophages polarization and pro-inflammatory cytokine, which were associated with reduction of JNK/P38/NFκB phosphorylation.

Potential drug discovery for COVID-19 treatment targeting Cathepsin L using a deep learning-based strategy.

Cathepsin L (CTSL), a cysteine protease that can cleave and activate the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, could be a promising therapeutic target for coronavirus disease 2019 (COVID-19). However, there is still no clinically available CTSL inhibitor that can be used. Here, we applied Chemprop, a newly trained directed-message passing deep neural network approach, to identify small molecules and FDA-approved drugs that can block CTSL activity to expand the discovery of CTSL inhibitors for drug development and repurposing for COVID-19. We found 5 molecules (Mg-132, Z-FA-FMK, leupeptin hemisulfate, Mg-101 and calpeptin) that were able to significantly inhibit the activity of CTSL in the nanomolar range and inhibit the infection of both pseudotype and live SARS-CoV-2. Notably, we discovered that daptomycin, an FDA-approved antibiotic, has a prominent CTSL inhibitory effect and can inhibit SARS-CoV-2 pseudovirus infection. Further, molecular docking calculation showed stable and robust binding of these compounds with CTSL. In conclusion, this study suggested for the first time that Chemprop is ideally suited to predict additional inhibitors of enzymes and revealed the noteworthy strategy for screening novel molecules and drugs for the treatment of COVID-19 and other diseases with unmet needs.

Abrogation of CC Chemokine Receptor 9 Ameliorates Ventricular Electrical Remodeling in Mice After Myocardial Infarction.

Introduction: Myocardial infarction (MI) triggers structural and electrical remodeling. CC chemokine receptor 9 (CCR9) mediates chemotaxis of inflammatory cells in MI. In our previous study, CCR9 knockout has been found to improve structural remodeling after MI. Here, we further investigate the potential influence of CCR9 on electrical remodeling following MI in order to explore potential new measures to improve the prognosis of MI. Methods and Results: Mice was used and divided into four groups: CCR9+/+/Sham, CCR9-/-/Sham, CCR9+/+/MI, CCR9-/-/MI. Animals were used at 1 week after MI surgery. Cardiomyocytes in the infracted border zone were acutely dissociated and the whole-cell patch clamp was used to record action potential duration (APD), L-type calcium current (I Ca,L ) and transient outward potassium current (I to ). Calcium transient and sarcoplasmic reticulum (SR) calcium content under stimulation of Caffeine were measured in isolated cardiomyocytes by confocal microscopy. Multielectrode array (MEA) was used to measure the conduction of the left ventricle. The western-blot was performed for the expression level of connexin 43. We observed prolonged APD90, increased I Ca,L and decreased I to following MI, while CCR9 knockout attenuated these changes (APD90: 50.57 ± 6.51 ms in CCR9-/-/MI vs. 76.53 ± 5.98 ms in CCR9+/+/MI, p < 0.05; I Ca,L : -13.15 ± 0.86 pA/pF in CCR9-/-/MI group vs. -17.05 ± 1.11 pA/pF in CCR9+/+/MI, p < 0.05; I to : 4.01 ± 0.17 pA/pF in CCR9-/-/MI group vs. 2.71 ± 0.16 pA/pF in CCR9+/+/MI, p < 0.05). The confocal microscopy results revealed CCR9 knockout reversed the calcium transient and calcium content reduction in sarcoplasmic reticulum following MI. MEA measurements showed improved conduction velocity in CCR9-/-/MI mice (290.1 ± 34.47 cm/s in CCR9-/-/MI group vs. 113.2 ± 14.4 cm/s in CCR9+/+/MI group, p < 0.05). Western-blot results suggested connexin 43 expression was lowered after MI while CCR9 knockout improved its expression. Conclusion: This study shows CCR9 knockout prevents the electrical remodeling by normalizing ion currents, the calcium homeostasis, and the gap junction to maintain APD and the conduction function. It suggests CCR9 is a promising therapeutic target for MI-induced arrhythmia, which warrants further investigation.

Fluvastatin attenuated ischemia/reperfusion-induced autophagy and apoptosis in cardiomyocytes through down-regulation HMGB1/TLR4 signaling pathway.

Fluvastatin, a traditional fat-decreasing drug, is widely used for curing cardiovascular disease. Previous reports demonstrated that fluvastatin pretreatment protected against myocardial ischemia/reperfusion (I/R) by inhibiting TLR4 signaling pathway and/or reducing proinflammatory cytokines. However, whether fluvastatin has a cardioprotective effect against apoptosis and autophagy remains unknown. This study aims to evaluate whether the cardioprotective role of fluvastatin in I/R is mediated by high-mobility group box 1 (HMGB1)/toll-like receptor 4 (TLR4) pathway via anti-apoptotic and anti-autophagic functions. Sprague-Dawley rats were anesthetized, artificially ventilated and subjected to 30 min of coronary occlusion, followed by 4 h of reperfusion. The animals were randomized into four groups: (i) Sham operation; (ii) I/R; (iii) I/R + low-dosage fluvastatin (10 mg/kg); and (iv) I/R + high-dosage fluvastatin (20 mg/kg). After reperfusion, the hemodynamic parameters, myocardial infarct size, structural alteration of myocardium, apoptosis index, pro-inflammatory cytokine production, Beclin-1, Light chain 3 (LC3), HMGB1, TLR4 and Nuclear factor kappa B (NF-κB) protein levels were measured and recorded. It was found that fluvastatin preconditioning improved left ventricular dysfunction, reduced HMGB1/TLR4/NF-κB expressions, and inhibited cardiomyocyte apoptosis, autophagy, and inflammation reaction. Moreover, treatment with fluvastatin ameliorated myocardial injury by reducing infarct size, causing less damage to cardiac structure, downregulating autophagy-related protein expression and releasing pro-inflammation mediators. Our findings indicate that fluvastatin exerts beneficial effects on cardiac ischemic damage, which may be associated with its anti-autophagic and anti-apoptotic functions via inhibition of HMGB1/TLR4-related pathway during I/R injury.

The Role of α7nAChR-Mediated Cholinergic Anti-Inflammatory Pathway in Vagal Nerve Regulated Atrial Fibrillation.

The aim was to investigate the role of the α7nAChR-mediated cholinergic anti-inflammatory pathway in vagal nerve regulated atrial fibrillation (AF).18 beagles (standard dogs for testing) were used in this study, and the effective refractory period (ERP) of atrium and pulmonary veins and AF inducibility were measured hourly during rapid atrial pacing at 800 beats/minute for 6 hours in all beagles. After cessation of 3 hours of RAP, the low-level vagal nerve stimulation (LL-VNS) group (n = 6) was given LL-VNS and injection of salinne (0.5 mL/GP) into four GPs, the methyllycaconitine (MLA, the antagonist of α7nAChR) group (n = 6) was given LL-VNS and injection of MLA into four GPs, and the Control group (n = 6) was given saline into four GPs and the right cervical vagal nerve was exposed without stimulation. Then, the levels of the tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), acetylcholine (ACh), STAT3, and NF-κB proteins were measured. During the first 3 hours of RAP, the ERPs gradually decreased while the dispersion of ERPs (dERPs) and AF inducibility gradually increased in all three groups. During the last 3 hours of 6 hours' RAP in this study, the ERPs in the LL-VNS group were higher, while the dERPs and AF inducibility were significantly lower when compared with the Control and MLA groups at the same time points. The levels of ACh in the serum and atrium in the LL-VNS and MLA groups were higher than in the Control group, and the levels of TNF-α and IL-6 were higher in the Control and MLA groups than in the LL-VNS group. The concentrations of STAT3 in RA and LA tissues were higher in the LL-VNS group while those of NF-κB were lower.In conclusion, the cholinergic anti-inflammatory pathway mediated by α7nACh plays an important role in low-level vagal nerve-regulated AF.

Over-Expression of Inhibitor of Differentiation 2 Attenuates Post-Infarct Cardiac Fibrosis Through Inhibition of TGF-ß1/Smad3/HIF-1α/IL-11 Signaling Pathway.

Background: Cardiac fibrosis after myocardial infarction mainly causes cardiac diastolic and systolic dysfunction, which results in fatal arrhythmias or even sudden death. Id2, a transcriptional repressor, has been shown to play an important role in the development of fibrosis in various organs, but its effects on cardiac fibrosis remain unclear. This study aimed to explore the effects of Id2 on cardiac fibrosis after myocardial infarction and its possible mechanisms. Methods: This study was performed in four experimental groups: control group, treatment group (including TGF-ß1, hypoxia or MI), treatment+GFP group and treatment+Id2 group. In vitro anoxic and fibrotic models were established by subjecting CFs or NRVMs to a three-gas incubator or TGF-ß1, respectively. An animal myocardial infarction model was established by ligating of the left anterior descending coronary artery followed by directly injecting of Id2 adenovirus into the myocardial infarct's marginal zone. Results: The results showed that Id2 significantly improved cardiac EF and attenuated cardiac hypertrophy. The mRNA and protein levels of α-SMA, Collagen I, Collagen III, MMP2 and TIMP1 were higher in treatment+Id2 group than those in treatment group as well as in treatment+GFP group both in vivo and in vitro. Immunofluorescence revealed that both α-SMA and vimentin were co-expressed in the treatment group and GFP group, but the co-expression were not detected in the control group and Id2 group. Additionally, our findings illustrated that Id2 had protective effects demonstrated by its ability to inhibit the TGF-ß1/Smad3/HIF-1α/IL-11 signaling pathways. Besides, over-expression of Id2 reduced cardiomyocytes apoptosis. Conclusion: In conclusion, this study demonstrated that over-expression of Id2 preserved cardiac function and ameliorated adverse cardiac remodeling, which might be a promising treatment target for cardiac fibrosis and apoptosis.

Transcription Factor prrx1 Promotes Brown Adipose-Derived Stem Cells Differentiation to Sinus Node-Like Cells.

This study investigated whether overexpression of paired-related homeobox 1 (prrx1) can successfully induce differentiation of brown adipose-derived stem cells (BADSCs) into sinus node-like cells. The experiments were performed in two groups: adenovirus-green fluorescent protein (Ad-GFP) group and Ad-prrx1 group. After 5-7 days of adenoviral transfection, the expression levels of sinus node cell-associated pacing protein (hyperpolarization-activated cyclic nucleotide-gated potassium channel 4 [HCN4]) and ion channel (calcium channel, voltage-dependent, T type, alpha 1G subunit [Cacna1g]), as well as transcription factors (T-box 18 [TBX18], insulin gene enhancer binding protein 1 [ISL-1], paired-like homeodomain transcription factor 2 [pitx2], short stature homeobox 2 [shox2]), were detected by western blot and reverse transcription-quantitative polymerase chain reaction. Immunofluorescence assay was carried out to detect whether prrx1 was coexpressed with HCN4, TBX18, and ISL-1. Finally, whole-cell patch-clamp technique was used to record pacing current hyperpolarization-activated inward current (If). The isolated cells were CD90+, CD29+, and CD45-, indicating that pure BADSCs were successfully isolated. After 5-7 days of Ad transfection into cells, the mRNA levels and protein levels of pacing-related factors (TBX18, ISL-1, HCN4, shox2, and Cacna1g) in Ad-prrx1 group were significantly higher than those in Ad-GFP group. However, the expression level of pitx2 was decreased. Immunofluorescence analysis showed that prrx1 was coexpressed with TBX18, ISL-1, and HCN4 in the Ad-prrx1 group, which did not appear in the Ad-GFP group. Whole-cell patch clamps were able to record the If current in the experimental group rather than in the Ad-GFP group. Overexpression of prrx1 can successfully induce sinus node-like cells.

C1q/TNF-related protein-9 attenuates retinal inflammation and protects blood-retinal barrier in db/db mice.

C1q/TNF-related protein-9(CTRP9) is an adipose cytokine, a closest adiponectin paralog, which has anti-inflammatory, antioxidant, vasodilation and anti-atherosclerosis effects. In addition, it can increase insulin sensitivity, decrease blood glucose level and inhibit the apoptosis of endothelial cells. However, it remains unclear whether CTRP9 has beneficial effects on diabetic retinopathy (DR). An adenoviral vector expressing CTRP9 was intravenously injected into db/db mice, aged 12 weeks, at day 15 post injection, and the process was repeated. The transfection efficiency of CTRP9 was assessed by enzyme linked immunosorbent assay. We used RT-PCR, immunofluorescence, and Western blot to determine proinflammatory cytokines, adhesion molecules and tight-junction proteins. The breakdown of blood-retinal barrier (BRB) was evaluated using Evans blue and retinal staining. CTRP9 suppresses the expression of interleukin-1 beta, tumor necrosis factor-alpha, monocyte chemotactic protein-1 and adhesion molecules in the retina of db/db mice. CTRP9 can balance the expression of pigment epithelium-derived factor and vascular endothelial growth factor. CTRP9 can also inhibit the activation of nuclear factor Kappa B in the retina of db/db mouse. In addition, CTRP9 can prevent the breakdown of BRB and downregulation of tight-junction proteins in the retina of db/db mice. Evans blue assay revealed the breakdown of BRB and vascular leakage in the retinas of diabetic mice. CTRP9 can both qualitatively and quantitatively alleviate the vascular leakage in the early stage of diabetic retinas. CTRP9 can inhibit the inflammation of diabetic retinopathy and protect blood-retinal barrier via decreasing proinflammatory cytokines and preventing the downregulation of tight-junction proteins.

[Responses of net ecosystem carbon exchange to diffuse radiation in an alpine meadow on the Qinghai-Tibetan Plateau, China.] / 青藏高原高寒草甸净生态系统碳交换对散射辐射变化的响应.

Qinghai-Tibetan Plateau, one of the regions on the earth that receives the most solar radiation, is the world's highest alpine meadow ecosystem, with significance to regional and global carbon cycles. To examine the effects of solar radiation on ecosystem carbon dynamics in an alpine meadow, the net ecosystem CO2 exchange (NEE), solar radiation, diffuse radiation, and related environmental variables were measured using eddy-covariance technique and micro-meteorological system. Sky conditions were divided into three categories of clear days (CI≥0.7), cloudy days (0.315 ℃. Under clear sky day conditions, Re increased with increasing CI due to the increases of air temperature, with negative effects on NEE. NEE increased with the increases of VPD up to 0.6 kPa, then slowly decreased when VPD>0.6 kPa, illustrating that NEE was reduced due to the relatively high VPD. Our results suggested that strong solar radiation on clear days would not increase carbon uptake capacity of alpine meadow, while cloudy days with clearness index of 0.6-0.7 would help increase carbon sequestration on the Qinghai-Tibetan Plateau.

Activin A inhibition attenuates sympathetic neural remodeling following myocardial infarction in rats.

Inflammation serves a critical role in driving sympathetic neural remodeling following myocardial infarction (MI), and activin A has been implicated as an important mediator of the inflammatory response post­MI. However, whether activin A impacts sympathetic neural remodeling post­MI remains unclear. In the present study, the authors assessed the effects of activin A on sympathetic neural remodeling in a rat model of MI. Rats were randomly divided into sham, MI, and MI + follistatin­300 (FS, activin A inhibitor) groups. Cardiac tissues from the peri­infarct zone were assessed for expression of sympathetic neural remodeling and inflammatory factors in rats 4 weeks post­MI by western blotting and immunohistochemical methods. Heart function was assessed by echocardiography. It is demonstrated that FS administration significantly reduced post­MI upregulation of activin A, nerve growth factor protein lever, and the density of nerve fibers with positive and protein expression of sympathetic neural remodeling markers in nerve fibers, which included growth associated protein 43 and tyrosine hydroxylase. In addition, inhibition of activin A reduced cardiac inflammation post­MI based on the reduction of i) interleukin­1 and tumor necrosis factor­α protein expression, ii) numbers and/or proportional area of infiltrating macrophages and myofibroblasts and iii) phosphorylated levels of p65 and IκBα. Furthermore, activin A inhibition lessened heart dysfunction post­MI. These results suggested that activin A inhibition reduced sympathetic neural remodeling post­MI in part through inhibition of the inflammatory response. The current study implicates activin A as a potential therapeutic target to circumvent sympathetic neural remodeling post-MI.

Effect of Shensong Yangxin on the Progression of Paroxysmal Atrial Fibrillation is Correlated with Regulation of Autonomic Nerve Activity.

BACKGROUND: Shensong Yangxin (SSYX), a traditional Chinese herbal medicine, has long been used clinically to treat arrhythmias in China. However, the mechanism of SSYX on atrial fibrillation (AF) is unknown. In this study, we tested the hypothesis that the effect of SSYX on the progression of paroxysmal AF is correlated with the regulation of autonomic nerve activity. METHODS: Eighteen mongrel dogs were randomly divided into control group (n = 6), pacing group (n = 6), and pacing + SSYX group (n = 6). The control group was implanted with pacemakers without pacing; the pacing group was implanted with pacemakers with long-term intermittent atrial pacing; the pacing + SSYX group underwent long-term intermittent atrial pacing and SSYX oral administration. RESULTS: Compared to the pacing group, the parameters of heart rate variability were lower after 8 weeks in the pacing + SSYX group (low-frequency [LF] component: 20.85 ± 3.14 vs. 15.3 ± 1.89 ms 2 , P = 0.004; LF component/high-frequency component: 1.34 ± 0.33 vs. 0.77 ± 0.15, P < 0.001). The atrial effective refractory period (AERP) was shorter and the dispersion of the AERP was higher after 8 weeks in the pacing group, while the changes were suppressed by SSYX intake. The dogs in the pacing group had more episodes and longer durations of AF than that in the pacing + SSYX group. SSYX markedly inhibited the increase in sympathetic nerves and upregulation of tumor necrosis factor-alpha and interleukin-6 expression in the pacing + SSYX group. Furthermore, SSYX suppressed the decrease of acetylcholine and α7 nicotinic acetylcholine receptor protein induced by long-term intermittent atrial pacing. CONCLUSIONS: SSYX substantially prevents atrial electrical remodeling and the progression of AF. These effects of SSYX may have association with regulating the imbalance of autonomic nerve activity and the cholinergic anti-inflammatory pathway.

TBX18 gene induces adipose-derived stem cells to differentiate into pacemaker-like cells in the myocardial microenvironment.

T-box 18 (TBX18) plays a crucial role in the formation and development of the head of the sinoatrial node. The objective of this study was to induce adipose-derived stem cells (ADSCs) to produce pacemaker-like cells by transfection with the TBX18 gene. A recombinant adenovirus vector carrying the human TBX18 gene was constructed to transfect ADSCs. The ADSCs transfected with TBX18 were considered the TBX18-ADSCs. The control group was the GFP-ADSCs. The transfected cells were co-cultured with neonatal rat ventricular cardiomyocytes (NRVMs). The results showed that the mRNA expression of TBX18 in TBX18-ADSCs was significantly higher than in the control group after 48 h and 7 days. After 7 days of co-culturing with NRVMs, there was no significant difference in the expression of the myocardial marker cardiac troponin I (cTnI) between the two groups. RT-qPCR and western blot analysis showed that the expression of HCN4 was higher in the TBX18-ADSCs than in the GFP-ADSCs. The If current was detected using the whole cell patch clamp technique and was blocked by the specific blocker CsCl. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSCMs) showed approximately twice the current density compared with the ADSCs. Our study indicated that the TBX18 gene induces ADSCs to differentiate into pacemaker­like cells in the cardiac microenvironment. Although further experiments are required in order to assess safety and efficacy prior to implementation in clinical practice, this technique may provide new avenues for the clinical therapy of bradycardia.

A novel peptide ghrelin inhibits neural remodeling after myocardial infarction in rats.

Ghrelin is a newly discovered peptide as an endogenous ligand for the growth hormone secretagogue receptor, and has been demonstrated to exert beneficial effect in the cardiovascular system. In the present study, we investigated whether ghrelin administration could inhibit cardiac neural remodeling and sympathetic hyperinnervation after myocardial infarction. Sprague-Dawley rats underwent coronary ligation to induce myocardial infarction and receiving ghrelin chronically (100 microg/kg s.c., twice daily) or saline control for 4 weeks after onset of ischemia. Four weeks after treatment, rats were sacrificed. We examined the expression of nerve growth factor and never markers as well as the mRNA expressions of inflammatory mediators in the infarcted border and non-infarcted left ventricular free wall. We also examined the NF-kappaBp65 protein and I-kappaBalpha protein levels by Western blot analysis. Compared to the control group, ghrelin administration significantly decreased the density of nerve fibers with positive immunostaining for GAP43 and TH, and decreased NGF mRNA and protein levels in the infarcted border and the non-infarcted area. Ghrelin also significantly suppressed interleukin-1beta, tumor necrosis factor-alpha, and endothelin-l mRNA expression, and inhibited NF-kappaB activation. In conclusion, treatment with ghrelin inhibited neural remodeling and sympathetic hyperinnervation, the process that may be associated with the inhibition of proinflammatory response and NGF signaling.

Changes of IK, ATP current density and allosteric modulation during chronic atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is the most common supraventricular arrhythmia in clinical practice. Chronic atrial fibrillation (CAF) is associated with ionic remodeling. However, little is known about the activity of ATP-sensitive potassium current (IK, ATP) during CAF. So we studied the changes of IK, ATP density and allosteric modulation of ATP-sensitivity by intracellular pH during CAF. METHODS: Myocardium samples were obtained from the right auricular appendage of patients with rheumatic heart disease complicated with valvular disease in sinus rhythm (SR) or CAF. There were 14 patients in SR group and 9 patients in CAF group. Single atrial cells were isolated using an enzyme dispersion technique. IK, ATP was recorded using the whole-cell and inside-out configuration of voltage-clamp techniques. In whole-cell model, myocytes of SR and CAF groups were perfused with simulated ischemic solution to elicit IK, ATP. In inside-out configuration, the internal patch membranes were exposed to different ATP concentrations in pH 7.4 and 6.8. RESULTS: Under simulated ischemia, IK, ATP current density of CAF group was significantly higher than in SR group [(83.5 +/- 10.8) vs. (58.7 +/- 8.4) pA/pF, P < 0.01]. IK, ATP of the two groups showed ATP concentration-dependent inhibition. The ATP concentration for 50% current inhibition (IC50) for the SR group was significantly different in pH 7.4 and pH 6.8 (24 vs. 74 micromol/L, P < 0.01). The IC50 did not change significantly in CAF group when the pH decreased from 7.4 to 6.8. CONCLUSIONS: During CAF, IK, ATP current density was increased and its allosteric modulation of ATP-sensitivity by intracellular pH was diminished.