Browsing by Author "Chen, Zhenhui"
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Item Amiodarone Inhibits Apamin-Sensitive Potassium Currents(Public Library of Science, 2013-07-29) Turker, Isik; Yu, Chih-Chieh; Chang, Po-Cheng; Chen, Zhenhui; Sohma, Yoshiro; Lin, Shien-Fong; Chen, Peng-Sheng; Ai, Tomohiko; Medicine, School of MedicineBackground: Apamin sensitive potassium current (I KAS), carried by the type 2 small conductance Ca(2+)-activated potassium (SK2) channels, plays an important role in post-shock action potential duration (APD) shortening and recurrent spontaneous ventricular fibrillation (VF) in failing ventricles. Objective: To test the hypothesis that amiodarone inhibits I KAS in human embryonic kidney 293 (HEK-293) cells. Methods: We used the patch-clamp technique to study I KAS in HEK-293 cells transiently expressing human SK2 before and after amiodarone administration. Results: Amiodarone inhibited IKAS in a dose-dependent manner (IC50, 2.67 ± 0.25 µM with 1 µM intrapipette Ca(2+)). Maximal inhibition was observed with 50 µM amiodarone which inhibited 85.6 ± 3.1% of IKAS induced with 1 µM intrapipette Ca(2+) (n = 3). IKAS inhibition by amiodarone was not voltage-dependent, but was Ca(2+)-dependent: 30 µM amiodarone inhibited 81.5±1.9% of I KAS induced with 1 µM Ca(2+) (n = 4), and 16.4±4.9% with 250 nM Ca(2+) (n = 5). Desethylamiodarone, a major metabolite of amiodarone, also exerts voltage-independent but Ca(2+) dependent inhibition of I KAS. Conclusion: Both amiodarone and desethylamiodarone inhibit I KAS at therapeutic concentrations. The inhibition is independent of time and voltage, but is dependent on the intracellular Ca(2+) concentration. SK2 current inhibition may in part underlie amiodarone's effects in preventing electrical storm in failing ventricles.Item Antiarrhythmic and proarrhythmic effects of subcutaneous nerve stimulation in ambulatory dogs(Elsevier, 2019) Wan, Juyi; Chen, Mu; Yuan, Yuan; Wang, Zhuo; Shen, Changyu; Fishbein, Michael C.; Chen, Zhenhui; Wong, Johnson; Grant, Maria B.; Everett, Thomas H., IV; Chen, Peng-Sheng; Medicine, School of MedicineBackground High output subcutaneous nerve stimulation (ScNS) remodels the stellate ganglia and suppresses cardiac arrhythmia. Objective To test the hypothesis that long duration low output ScNS causes cardiac nerve sprouting, increases plasma norepinephrine concentration and the durations of paroxysmal atrial tachycardia (PAT) in ambulatory dogs. Methods We prospectively randomized 22 dogs (11 males and 11 females) into 5 different output groups for 2 months of ScNS: 0 mA (sham) (N=6), 0.25 mA (N=4), 1.5 mA (N=4), 2.5 mA (N=4) and 3.5 mA (N=4). Results As compared with baseline, the changes of the durations of PAT episodes per 48 hours were significantly different among different groups (sham, -5.0±9.5 s; 0.25 mA 95.5±71.0 s; 1.5 mA, -99.3±39.6 s; 2.5 mA, -155.3±87.8 s and 3.5 mA, -76.3±44.8 s, p<0.001). The 3.5 mA group had greater reduction of sinus heart rate than the sham group (-29.8±15.0 bpm vs -14.5±3.0 bpm, p=0.038). Immunohistochemical studies showed that the 0.25 mA group had a significantly increased while 2.5 mA and 3.5 mA stimulation had a significantly reduced growth-associated protein 43 nerve densities in both atria and ventricles. The plasma Norepinephrine concentrations in 0.25 mA group was 5063.0±4366.0 pg/ml, which was significantly higher than other groups of dogs (739.3±946.3, p=0.009). There were no significant differences in the effects of simulation between males and females. Conclusions In ambulatory dogs, low output ScNS causes cardiac nerve sprouting, increases plasma norepinephrine concentration and the duration of PAT episodes while high output ScNS is antiarrhythmic.Item Antiarrhythmic effects of stimulating the left dorsal branch of the thoracic nerve in a canine model of paroxysmal atrial tachyarrhythmias(Elsevier, 2018) Zhao, Ye; Yuan, Yuan; Tsai, Wei-Chung; Jiang, Zhaolei; Tian, Zhi-peng; Shen, Changyu; Lin, Shien-Fong; Fishbein, Michael C.; Everett, Thomas H., IV.; Chen, Zhenhui; Chen, Peng-Sheng; Medicine, School of MedicineBackground Stellate ganglion nerve activity (SGNA) precedes paroxysmal atrial tachyarrhythmia (PAT) episodes in dogs with intermittent high-rate left atrial (LA) pacing. The left dorsal branch of the thoracic nerve (LDTN) contains sympathetic nerves originating from the stellate ganglia. Objective The purpose of this study was to test the hypothesis that high-frequency electrical stimulation of the LDTN can cause stellate ganglia damage and suppress PAT. Methods We performed chronic LDTN stimulation in 6 dogs with and 2 dogs without intermittent rapid LA pacing while monitoring SGNA. Results LDTN stimulation reduced average SGNA from 4.36 μV (95% confidence interval [CI] 4.10–4.62 μV) at baseline to 3.22 μV (95% CI 3.04–3.40 μV) after 2 weeks (P = .028) and completely suppressed all PAT episodes in all dogs studied. Tyrosine hydroxylase staining showed large damaged regions in both stellate ganglia, with increased percentages of tyrosine hydroxylase–negative cells. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed that 23.36% (95% CI 18.74%–27.98%) of ganglion cells in the left stellate ganglia and 11.15% (95% CI 9.34%–12.96%) ganglion cells in the right stellate ganglia were positive, indicating extensive cell death. A reduction of both SGNA and heart rate was also observed in dogs with LDTN stimulation but without high-rate LA pacing. Histological studies in the latter 2 dogs confirmed the presence of extensive stellate ganglia damage, along with a high percentage of terminal deoxynucleotidyl transferase dUTP nick end labeling–positive cells. Conclusion LDTN stimulation damages both left stellate ganglia and right stellate ganglia, reduces left SGNA, and is antiarrhythmic in this canine model of PAT.Item Apamin-Sensitive Calcium-Activated Potassium Currents in Rabbit Ventricles with Chronic Myocardial Infarction(Wiley Online Library, 2013-10-24) Lee, Young Soo; Chang, Po-Cheng; Hsueh, Chia-Hsiang; Maruyama, Mitsunori; Park, Hyung Wook; Rhee, Kyoung-Suk; Hsieh, Yu-Cheng; Shen, Changyu; Weiss, James N.; Chen, Zhenhui; Lin, Shien-Fong; Chen, Peng-Sheng; Department of Medicine, IU School of MedicineIntroduction Apamin-sensitive small-conductance calcium-activated potassium current (IKAS) is increased in heart failure. It is unknown if myocardial infarction (MI) is also associated with an increase of IKAS. Methods and Results We performed Langendorff perfusion and optical mapping in 6 normal hearts and 10 hearts with chronic (5 weeks) MI. An additional 6 normal and 10 MI hearts were used for patch clamp studies. The infarct size was 25% [95% confidence interval, 20 to 31] and the left ventricular ejection fraction was 0.5 [0.46 to 0.54]. The rabbits did not have symptoms of heart failure. The action potential duration measured to 80% repolarization (APD80) in the peri-infarct zone (PZ) was150 [142 to 159] ms, significantly (p=0.01) shorter than in the normal ventricles (158 to 177] ms). The intracellular Ca transient duration was also shorter in the PZ (148 [139 to 157] ms) than in normal ventricles (168 [157 to 180] ms; P=0.017). Apamin prolonged the APD80 in PZ by 9.8 [5.5 to 14.1] %, which is greater than in normal ventricles (2.8 [1.3 to 4.3] %, p=0.006). Significant shortening of APD80 was observed at the cessation of rapid pacing in MI but not in normal ventricles. Apamin prevented postpacing APD80 shortening. Patch clamp studies showed that IKAS was significantly higher in the PZ cells (2.51 [1.55 to 3.47] pA/pF, N=17) than in the normal cells (1.08 [0.36 to 1.80] pA/pF, N=15, p=0.019). Conclusion We conclude that IKAS is increased in MI ventricles and contributes significantly to ventricular repolarization especially during tachycardia.Item Arrhythmogenic Calmodulin Mutations Impede Activation of Small-conductance Calcium-Activated Potassium Current(Elsevier, 2016-08) Yu, Chih-Chieh; Ko, Jum-Suk; Ai, Tomohiko; Tsai, Wen-Chin; Chen, Zhenhui; Rubart, Michael; Vatta, Matteo; Everett, Thomas H.; George, Alfred L.; Chen, Peng-Sheng; Medicine, School of MedicineBackground Apamin sensitive small-conductance Ca2+-activated K+ (SK) channels are gated by intracellular Ca2+ through a constitutive interaction with calmodulin. Objective We hypothesize that arrhythmogenic human calmodulin mutations impede activation of SK channels. Methods We studied 5 previously published calmodulin mutations (N54I, N98S, D96V, D130G and F90L). Plasmids encoding either wild type (WT) or mutant calmodulin were transiently transfected into human embryonic kidney (HEK) 293 cells that stably express SK2 channels (SK2 Cells). Whole-cell voltage-clamp recording was used to determine apamin-sensitive current (IKAS) densities. We also performed optical mapping studies in normal murine hearts to determine the effects of apamin in hearts with (N=7) or without (N=3) pretreatment with sea anemone toxin (ATX II). Results SK2 cells transfected with WT calmodulin exhibited IKAS density (in pA/pF) of 33.6 [31.4;36.5] (median and confidence interval 25%-75%), significantly higher than that observed for cells transfected with N54I (17.0 [14.0;27.7], p=0.016), F90L (22.6 [20.3;24.3], p=0.011), D96V (13.0 [10.9;15.8], p=0.003), N98S (13.7 [8.8;20.4], p=0.005) and D130G (17.6 [13.8;24.6], p=0.003). The reduction of SK2 current was not associated with a decrease in membrane protein expression or intracellular distribution of the channel protein. Apamin increased the ventricular APD80 (from 79.6 ms [63.4-93.3] to 121.8 ms [97.9-127.2], p=0.010) in hearts pre-treated with ATX-II but not in control hearts. Conclusion Human arrhythmogenic calmodulin mutations impede the activation of SK2 channels in HEK 293 cells.Item Concomitant SK current activation and sodium current inhibition cause J wave syndrome(American Society for Clinical Investigation, 2018-11-15) Chen, Mu; Xu, Dong-Zhu; Wu, Adonis Z.; Guo, Shuai; Wan, Juyi; Yin, Dechun; Lin, Shien-Fong; Chen, Zhenhui; Rubart-von der Lohe, Michael; Everett, Thomas H., IV; Qu, Zhilin; Weiss, James N.; Chen, Peng-Sheng; Medicine, School of MedicineThe mechanisms of J wave syndrome (JWS) are incompletely understood. Here, we showed that the concomitant activation of small-conductance calcium-activated potassium (SK) current (IKAS) and inhibition of sodium current by cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine (CyPPA) recapitulate the phenotypes of JWS in Langendorff-perfused rabbit hearts. CyPPA induced significant J wave elevation and frequent spontaneous ventricular fibrillation (SVF), as well as sinus bradycardia, atrioventricular block, and intraventricular conduction delay. IKAS activation by CyPPA resulted in heterogeneous shortening of action potential (AP) duration (APD) and repolarization alternans. CyPPA inhibited cardiac sodium current (INa) and decelerated AP upstroke and intracellular calcium transient. SVFs were typically triggered by short-coupled premature ventricular contractions, initiated with phase 2 reentry and originated more frequently from the right than the left ventricles. Subsequent IKAS blockade by apamin reduced J wave elevation and eliminated SVF. β-Adrenergic stimulation was antiarrhythmic in CyPPA-induced electrical storm. Like CyPPA, hypothermia (32.0°C) also induced J wave elevation and SVF. It facilitated negative calcium-voltage coupling and phase 2 repolarization alternans with spatial and electromechanical discordance, which were ameliorated by apamin. These findings suggest that IKAS activation contributes to the development of JWS in rabbit ventricles.Item Effects of ondansetron on apamin-sensitive small conductance calcium-activated potassium currents in pacing-induced failing rabbit hearts(Elsevier, 2019) Yin, Dechun; Yang, Na; Tian, Zhipeng; Wu, Adonis Z.; Xu, Dongzhu; Chen, Mu; Kamp, Nicholas J.; Wang, Zhuo; Shen, Changyu; Chen, Zhenhui; Lin, Shien-Fong; Rubart-von der Lohe, Michael; Chen, Peng-Sheng; Everett, Thomas H., IV; Medicine, School of MedicineBackground Ondansetron, a widely prescribed antiemetic, has been implicated in drug-induced long QT syndrome. Recent patch clamp experiments have shown that ondansetron inhibits the apamin-sensitive small conductance calcium-activated potassium current (IKAS). Objective The purpose of this study was to determine whether ondansetron causes action potential duration (APD) prolongation by IKAS inhibition. Methods Optical mapping was performed in rabbit hearts with pacing-induced heart failure (HF) and in normal hearts before and after ondansetron (100 nM) infusion. APD at 80% repolarization (APD80) and arrhythmia inducibility were determined. Additional studies with ondansetron were performed in normal hearts perfused with hypokalemic Tyrode's (2.4 mM) solution before or after apamin administration. Results The corrected QT interval in HF was 326 ms (95% confidence interval [CI] 306–347 ms) at baseline and 364 ms (95% CI 351–378 ms) after ondansetron infusion (P < .001). Ondansetron significantly prolonged APD80 in the HF group and promoted early afterdepolarizations, steepened the APD restitution curve, and increased ventricular vulnerability. Ventricular fibrillation was not inducible in HF ventricles at baseline, but after ondansetron infusion, ventricular fibrillation was induced in 5 of the 7 ventricles (P = .021). In hypokalemia, apamin prolonged APD80 from 163 ms (95% CI 146–180 ms) to 180 ms (95% CI 156–204 ms) (P = .018). Subsequent administration of ondansetron failed to further prolong APD80 (180 ms [95% CI 156–204 ms] vs 179 ms [95% CI 165–194 ms]; P = .789). The results were similar when ondansetron was administered first, followed by apamin. Conclusion Ondansetron is a specific IKAS blocker at therapeutic concentrations. Ondansetron may prolong the QT interval in HF by inhibiting small conductance calcium-activated potassium channels, which increases the vulnerability to ventricular arrhythmias.Item Effects of renal sympathetic denervation on the stellate ganglion and brain stem in dogs(Elsevier, 2017-02) Tsai, Wei-Chung; Chan, Yi-Hsin; Chinda, Kroekkiat; Chen, Zhenhui; Patel, Jheel; Shen, Changyu; Zhao, Ye; Jiang, Zhaolei; Yuan, Yuan; Ye, Michael; Chen, Lan S.; Riley, Amanda A.; Persohn, Scott A.; Territo, Paul R.; Everett, Thomas H., IV; Lin, Shien-Fong; Vinters, Harry V.; Fishbein, Michael C.; Chen, Peng-Sheng; Medicine, School of MedicineBACKGROUND: Renal sympathetic denervation (RD) is a promising method of neuromodulation for the management of cardiac arrhythmia. OBJECTIVE: We tested the hypothesis that RD is antiarrhythmic in ambulatory dogs because it reduces the stellate ganglion nerve activity (SGNA) by remodeling the stellate ganglion (SG) and brain stem. METHODS: We implanted a radiotransmitter to record SGNA and electrocardiogram in 9 ambulatory dogs for 2 weeks, followed by a second surgery for RD and 2 months SGNA recording. Cell death was probed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. RESULTS: Integrated SGNA at baseline and 1 and 2 months after RD were 14.0 ± 4.0, 9.3 ± 2.8, and 9.6 ± 2.0 μV, respectively (P = .042). The SG from RD but not normal control dogs (n = 5) showed confluent damage. An average of 41% ± 10% and 40% ± 16% of ganglion cells in the left and right SG, respectively, were TUNEL positive in RD dogs compared with 0% in controls dogs (P = .005 for both). The left and right SG from RD dogs had more tyrosine hydroxylase-negative ganglion cells than did the left SG of control dogs (P = .028 and P = .047, respectively). Extensive TUNEL-positive neurons and glial cells were also noted in the medulla, associated with strongly positive glial fibrillary acidic protein staining. The distribution was heterogeneous, with more cell death in the medial than lateral aspects of the medulla. CONCLUSION: Bilateral RD caused significant central and peripheral sympathetic nerve remodeling and reduced SGNA in ambulatory dogs. These findings may in part explain the antiarrhythmic effects of RD.Item Heterogeneous Upregulation of Apamin‐Sensitive Potassium Currents in Failing Human Ventricles(American Heart Association, 2013-01-03) Chang, Po-Cheng; Turker, Isik; Lopshire, John C.; Masroor, Saqib; Nguyen, Bich-Lien; Tao, Wen; Rubart, Michael; Chen, Peng-Sheng; Chen, Zhenhui; Ai, Tomohiko; Medicine, School of MedicineBackground: We previously reported that IKAS are heterogeneously upregulated in failing rabbit ventricles and play an important role in arrhythmogenesis. This study goal is to test the hypothesis that subtype 2 of the small-conductance Ca(2+) activated K(+) (SK2) channel and apamin-sensitive K(+) currents (IKAS) are upregulated in failing human ventricles. Methods and results: We studied 12 native hearts from transplant recipients (heart failure [HF] group) and 11 ventricular core biopsies from patients with aortic stenosis and normal systolic function (non-HF group). IKAS and action potential were recorded with patch-clamp techniques, and SK2 protein expression was studied by Western blotting. When measured at 1 μmol/L Ca(2+) concentration, IKAS was 4.22 (median) (25th and 75th percentiles, 2.86 and 6.96) pA/pF for the HF group (n=11) and 0.98 (0.54 and 1.72) pA/pF for the non-HF group (n=8, P=0.008). IKAS was lower in the midmyocardial cells than in the epicardial and the endocardial cells. The Ca(2+) dependency of IKAS in HF myocytes was shifted leftward compared to non-HF myocytes (Kd 314 versus 605 nmol/L). Apamin (100 nmol/L) increased the action potential durations by 1.77% (-0.9% and 7.3%) in non-HF myocytes and by 11.8% (5.7% and 13.9%) in HF myocytes (P=0.02). SK2 protein expression was 3-fold higher in HF than in non-HF. Conclusions: There is heterogeneous upregulation of IKAS densities in failing human ventricles. The midmyocardial layer shows lower IKAS densities than epicardial and endocardial layers of cells. Increase in both Ca(2+) sensitivity and SK2 protein expression contributes to the IKAS upregulation.Item Indirect Correlative Light and Electron Microscopy (iCLEM): A Novel Pipeline for Multiscale Quantification of Structure From Molecules to Organs(Oxford University Press, 2024) Struckman, Heather L.; Moise, Nicolae; Vanslembrouck, Bieke; Rothacker, Nathan; Chen, Zhenhui; van Hengel, Jolanda; Weinberg, Seth H.; Veeraraghavan, Rengasayee; Medicine, School of MedicineCorrelative light and electron microscopy (CLEM) methods are powerful methods that combine molecular organization (from light microscopy) with ultrastructure (from electron microscopy). However, CLEM methods pose high cost/difficulty barriers to entry and have very low experimental throughput. Therefore, we have developed an indirect correlative light and electron microscopy (iCLEM) pipeline to sidestep the rate-limiting steps of CLEM (i.e., preparing and imaging the same samples on multiple microscopes) and correlate multiscale structural data gleaned from separate samples imaged using different modalities by exploiting biological structures identifiable by both light and electron microscopy as intrinsic fiducials. We demonstrate here an application of iCLEM, where we utilized gap junctions and mechanical junctions between muscle cells in the heart as intrinsic fiducials to correlate ultrastructural measurements from transmission electron microscopy (TEM), and focused ion beam scanning electron microscopy (FIB-SEM) with molecular organization from confocal microscopy and single molecule localization microscopy (SMLM). We further demonstrate how iCLEM can be integrated with computational modeling to discover structure-function relationships. Thus, we present iCLEM as a novel approach that complements existing CLEM methods and provides a generalizable framework that can be applied to any set of imaging modalities, provided suitable intrinsic fiducials can be identified.