Browsing by Author "Chan, Yi-Hsin"

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Acute reversal of phospholamban inhibition facilitates the rhythmic whole-cell propagating calcium waves in isolated ventricular myocytes
(2015-03-01)
Chan, Yi-Hsin
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Tsai, Wei-Chung
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Song, Zhen
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Ko, Christopher Y.
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Qu, Zhilin
Phospholamban (PLB) inhibits the activity of cardiac sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a). Phosphorylation of PLB during sympathetic activation reverses SERCA2a inhibition, increasing SR Ca2+ uptake. However, sympathetic activation also modulates multiple other intracellular targets in ventricular myocytes (VMs), making it impossible to determine the specific effects of the reversal of PLB inhibition on the spontaneous SR Ca2+ release. Therefore, it remains unclear how PLB regulates rhythmic activity in VMs. Here, we used the Fab fragment of 2D12, a monoclonal anti-PLB antibody, to test how acute reversal of PLB inhibition affects the spontaneous SR Ca2+ release in normal VMs. Ca2+ sparks and spontaneous Ca2+ waves (SCWs) were recorded in the line-scan mode of confocal microscopy using the Ca2+ fluorescent dye Fluo-4 in isolated permeabilized mouse VMs. Fab, which reverses PLB inhibition, significantly increased the frequency, amplitude, and spatial/temporal spread of Ca2+ sparks in VMs exposed to 50 nM free [Ca2+]. At physiological diastolic free [Ca2+] (100-200 nM), Fab facilitated the formation of whole-cell propagating SCWs. At higher free [Ca2+], Fab increased the frequency and velocity, but decreased the decay time of the SCWs. cAMP had little additional effect on the frequency or morphology of Ca2+ sparks or SCWs after Fab addition. These findings were complemented by computer simulations. In conclusion, acute reversal of PLB inhibition alone significantly increased the spontaneous SR Ca2+ release, leading to the facilitation and organization of whole-cell propagating SCWs in normal VMs. PLB thus plays a key role in subcellular Ca2+ dynamics and rhythmic activity of VMs. (C) 2015 Elsevier Ltd. All rights reserved.
Effects of renal sympathetic denervation on the stellate ganglion and brain stem in dogs
(2017-02-01)
Tsai, Wei-Chung
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Chan, Yi-Hsin
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Chinda, Kroekkiat
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Chen, Zhenhui
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Patel, Jheel
BACKGROUND 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 mu V, 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.
Intermittent left cervical vagal nerve stimulation damages the stellate ganglia and reduces the ventricular rate during sustained atrial fibrillation in ambulatory dogs
(2016-03)
Chinda, Kroekkiat
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Tsai, Wei-Chung
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Chan, Yi-Hsin
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Lin, Andrew Y-T
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Patel, Jheel
BACKGROUND The effects of intermittent open-loop vagal nerve stimulation (VNS) on the ventricular rate (VR) during atrial fibrillation (AF) remain unclear. OBJECTIVE The purpose of this study was to test the hypothesis that VNS damages the stellate ganglion (SG) and improves VR control during persistent AF. METHODS We performed left cervical VNS in ambulatory dogs while recording the left SG nerve activity (SGNA) and vagal nerve activity. Tyrosine hydroxylase (TH) staining and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to assess neuronal cell death in the SG. RESULTS We induced persistent AF by atrial pacing in 6 dogs, followed by intermittent VNS with short ON-time (14 seconds) and long OFF-time (66 seconds). The integrated SGNA and VR during AF were 4.84 mV . s (95% confidence interval [CI] 3.08-6.60 mV . s) and 142 beats/min (95% CI 116-168 beats/min), respectively. During AF, VNS reduced the integrated SGNA and VR, respectively, to 3.74 mV . s (95% CI 2.27-5.20 mV . s; P =.021) and 115 beats/ min (95% CI 96-134 beats/min; P =.016) during 66-second OFF-time and to 4.07 mV . s (95% CI 2.42-5.72 mV . s; P =.037) and 114 beats/min (95% CI 83-146 beats/min; P =.039) during 3-minute OFF-time. VNS increased the frequencies of prolonged (>3 seconds) pauses during AF. TH staining showed large confluent areas of damage in the left SG, characterized by pyknotic nuclei, reduced TH staining, increased percentage of TH-negative ganglion cells, and positive TUNEL staining. Occasional TUN EL-positive ganglion cells were also observed in the right SG. CONCLUSION VNS damaged the SG, leading to reduced SGNA and better rate control during persistent AF.
Role of Apamin-Sensitive Calcium-Activated Small-Conductance Potassium Currents on the Mechanisms of Ventricular Fibrillation in Pacing-Induced Failing Rabbit Hearts
(2017-02-01)
Yin, Dechun
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Hsieh, Yu-Cheng
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Tsai, Wei-Chung
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Wu, Adonis Zhi-Yang
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Jiang, Zhaolei
Background-Ventricular fibrillation (VF) during heart failure is characterized by stable reentrant spiral waves (rotors). Apamin-sensitive small-conductance calcium-activated potassium currents (I-KAS) are heterogeneously upregulated in failing hearts. We hypothesized that I-KAS influences the location and stability of rotors during VF. Methods and Results-Optical mapping was performed on 9 rabbit hearts with pacing-induced heart failure. The epicardial right ventricular and left ventricular surfaces were simultaneously mapped in a Langendorff preparation. At baseline and after apamin (100 nmol/L) infusion, the action potential duration (APD(80)) was determined, and VF was induced. Areas with a >50% increase in the maximum action potential duration (Delta APD) after apamin infusion were considered to have a high I-KAS distribution. At baseline, the distribution density of phase singularities during VF in high I-KAS distribution areas was higher than in other areas (0.0035 +/- 0.0011 versus 0.0014 +/- 0.0010 phase singularities/pixel; P=0.004). In addition, high dominant frequencies also colocalized to high I-KAS distribution areas (26.0 versus 17.9 Hz; P=0.003). These correlations were eliminated during VF after apamin infusion, as the number of phase singularities (17.2 versus 11.0; P=0.009) and dominant frequencies (22.1 versus 16.2 Hz; P=0.022) were all significantly decreased. In addition, reentrant spiral waves became unstable after apamin infusion, and the duration of VF decreased. Conclusions-The I-KAS current influences the mechanism of VF in failing hearts as phase singularities, high dominant frequencies, and reentrant spiral waves all correlated to areas of high I-KAS. Apamin eliminated this relationship and reduced VF vulnerability.
Role of apamin-sensitive small conductance calcium-activated potassium currents in long-term cardiac memory in rabbits
(2018-05-01)
Yin, Dechun
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Chen, Mu
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Yang, Na
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Wu, Adonis Z.
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Xu, Dongzhu
BACKGROUND Apamin-sensitive small conductance calcium-activated K current (I-KAS) is up-regulated during ventricular pacing and masks short-term cardiac memory (CM). OBJECTIVE The purpose of this study was to determine the role of I-KAS in long-term CM. METHODS CM was created with 3-5 weeks of ventricular pacing and defined by a flat or inverted T wave off pacing. Epicardial optical mapping was performed in both paced and normal ventricles. Action potential duration (APD(80)) was determined during right atrial pacing. Ventricular stability was tested before and after I-KAS blockade. Four paced hearts and 4 normal hearts were used for western blotting and histology. RESULTS There were no significant differences in either echocardiographic parameters or fibrosis levels between groups. Apamin induced more APD(80) prolongation in CM than in normal ventricles (mean [95% confidence interval]: 9.6% [8.8%-10.5%] vs 3.1% [1.9%-4.3%]; P <.001). Apamin significantly lengthened APD(80) in the CM model at late activation sites, indicating significant I-KAS up-regulation at those sites. The CM model also had altered Ca2+ handling, with the 50% Ca2+ transient duration and amplitude increased at distal sites compared to a proximal site (near the pacing site). After apamin, the CM model had increased ventricular fibrillation (VF) inducibility (paced vs control: 33/40 (82.5%) vs 7/20 (35%); P < .001) and longer VF durations (124 vs 26 seconds; P < .001). CONCLUSION Chronic ventricular pacing increases Ca2+ transients at late activation sites, which activates I-KAS to maintain repolarization reserve. I-KAS blockade increases VF vulnerability in chronically paced rabbit ventricles.
Small conductance calcium-activated potassium current and the mechanism of atrial arrhythmia in mice with dysfunctional melanocyte-like cells
(2016-07)
Tsai, Wei-Chung
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Chan, Yi-Hsin
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Hsueh, Chia-Hsiang
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Everett, Thomas H.
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Chang, Po-Cheng
BACKGROUND The melanin synthesis enzyme dopachrome tautomerase (Dct) regulates intracellular Ca2+ in melanocytes. Homozygous Dct knockout (Dct(-/-)) adult mice are vulnerable to atrial arrhythmias (AA). OBJECTIVE The purpose of this study was to determine whether apamin-sensitive small conductance Ca2+-activated K+ (SK) currents are upregulated in Dct(-/-) mice and contribute to AA. METHODS Optical mapping was used to study the membrane potential of the right atrium in Langendorff perfused Dct(-/-) (n = 9) and Dct(+/-) (n = 9) mice. RESULTS Apamin prolonged action potential duration (APD) by 18.8 ms (95% confidence interval [CI] 13.4-24.1 ms) in Dct(-/-) mice and by 11.5 ms (95% CI 5.4-17.6 ms) in Dct(+/-) mice at a pacing cycle length of 150 ms (P = .047). The pacing cycle length threshold to induce APD alternans was 48 ms (95% CI 34-62 ms) for Dct(-/-) mice and 21 ms (95% CI 12-29 ms) for Dct(+/-) mice (P = .002) at baseline, and it was 35 ms (95% CI 21-49 ms) for Dct(-/-) mice and 22 ms (95% CI 11-32 ms) for Dct(+/-) mice (P = .025) after apamin administration. Apamin prolonged post-burst pacing APD by 8.9 ms (95% CI 3.9-14.0 ms) in Dct(-/-) mice and by 1.5 ms (95% CI 0.7-2.3 ms) in Dct(+/-) mice (P = .005). Immunoblot and quantitative polymerase chain reaction analyses showed that protein and transcripts levels of SK1 and SK3 were increased in the right atrium of Dct(-/-) mice. AA inducibility (89% vs 11%; P = .003) and duration (281 seconds vs 66 seconds; P = .008) were greater in Dct(-/-) mice than in Dct(+/-) mice at baseline, but not different (22% vs 11%; P = 1.00) after apamin administration. Five of 8 (63%) induced atrial fibrillation episodes in Dct(-/-) mice had focal drivers. CONCLUSION Apamin-sensitive SK current upregulation in Dct(-/-) mice plays an important role in the mechanism of AA.
Small-Conductance Calcium-Activated Potassium Current Is Activated During Hypokalemia and Masks Short-Term Cardiac Memory Induced by Ventricular Pacing
(2015-10-13)
Chan, Yi-Hsin
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Tsai, Wei-Chung
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Ko, Jum-Suk
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Yin, Dechun
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Chang, Po-Cheng
Background-Hypokalemia increases the vulnerability to ventricular fibrillation. We hypothesize that the apamin-sensitive small-conductance calcium-activated potassium current (I-KAS) is activated during hypokalemia and that I-KAS blockade is proarrhythmic. Methods and Results-Optical mapping was performed in 23 Langendorff-perfused rabbit ventricles with atrioventricular block and either right or left ventricular pacing during normokalemia or hypokalemia. Apamin prolonged the action potential duration (APD) measured to 80% repolarization (APD(80)) by 26 milliseconds (95% confidence interval [CI], 14-37) during normokalemia and by 54 milliseconds (95% CI, 40-68) during hypokalemia (P=0.01) at a 1000-millisecond pacing cycle length. In hypokalemic ventricles, apamin increased the maximal slope of APD restitution, the pacing cycle length threshold of APD alternans, the pacing cycle length for wave-break induction, and the area of spatially discordant APD alternans. Apamin significantly facilitated the induction of sustained ventricular fibrillation (from 3 of 9 hearts to 9 of 9 hearts; P=0.009). Short-term cardiac memory was assessed by the slope of APD(80) versus activation time. The slope increased from 0.01 (95% CI, -0.09 to 0.12) at baseline to 0.34 (95% CI, 0.23-0.44) after apamin (P<0.001) during right ventricular pacing and from 0.07 (95% CI, -0.05 to 0.20) to 0.54 (95% CI, 0.06-1.03) after apamin infusion (P=0.045) during left ventricular pacing. Patch-clamp studies confirmed increased I-KAS in isolated rabbit ventricular myocytes during hypokalemia (P=0.038). Conclusions-Hypokalemia activates I-KAS to shorten APD and maintain repolarization reserve at late activation sites during ventricular pacing. I-KAS blockade prominently lengthens the APD at late activation sites and facilitates ventricular fibrillation induction.
Subcutaneous nerve activity is more accurate than heart rate variability in estimating cardiac sympathetic tone in ambulatory dogs with myocardial infarction
(2015-07-01)
Chan, Yi-Hsin
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Tsai, Wei-Chung
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Shen, Changyu
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Han, Seongwook
;
Chen, Lan S.
BACKGROUND We recently reported that subcutaneous nerve activity (SCNA) can be used to estimate sympathetic tone. OBJECTIVE The purpose of this study was to test the hypothesis that left thoracic SCNA is more accurate than heart rate variability (HRV) in estimating cardiac sympathetic tone in ambulatory dogs with myocardial infarction (MI). METHODS We used an implanted radiotransmitter to study left stellate ganglion nerve activity (SGNA), vagal nerve activity (VNA), and thoracic SCNA in 9 dogs at baseline and up to 8 weeks after MI. HRV was determined based on time-domain, frequency-domain, and nonlinear analyses. RESULTS The correlation coefficients between integrated SGNA and SCNA averaged 0.74 (95% confidence interval [CI] 0.41-1.06) at baseline and 0.82 (95% CI, 0.63-1.01) after MI (P <.05 for both). The absolute values of the correlation coefficients were significantly larger than that between SGNA and HRV analysis based on time-domain, frequency-domain, and nonlinear analyses, respectively, at baseline (P <.05 for all) and after MI (P <.05 for all). There was a clear increment of SGNA and SCNA at 2, 4, 6, and 8 weeks after MI, whereas HRV parameters showed no significant changes. Significant circadian variations were noted in SCNA, SGNA, and all HRV parameters at baseline and after MI, respectively. Atrial tachycardia (AT) episodes were invariably preceded by SCNA and SGNA, which were progressively increased from 120th, 90th, 60th, to 30th seconds before AT onset. No such changes of HRV parameters were observed before AT onset. CONCLUSION SCNA is more accurate than HRV in estimating cardiac sympathetic tone in ambulatory dogs with MI.