Abstract 500: High Basal Ca 2+ / Calmodulin Kinase II Activity Modulates Spontaneous Sarcoplasmic Reticulum Ca 2+ Cycling That Drives Normal Automaticity in Sinoatrial Nodal Cells

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Yue Li ◽  
Syevda G. Sirenko ◽  
Tatiana M. Vinogradova ◽  
Alexey E. Lyashkov ◽  
Weizhong Zhu ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Surface Membrane ◽  
Phosphorylation Site ◽  
Major Effect ◽  
Physiological Solution ◽  
Confocal Imaging ◽  
Ventricular Cells ◽  
Calmodulin Kinase ◽  
Recovery From Inactivation ◽  
And Control

The crucial dependence of normal automaticity of sinoatrial nodal cells (SANC) on CaMKII signaling has previously been linked to an effect to facilitate recovery from inactivation of L-type Ca 2+ channels. More recently, however, it has been discovered that spontaneous, rhythmic, local Ca 2+ releases (LCR’s) from sarcoplasmic reticulum (SR) activate Na + /Ca 2+ exchanger current, imparting an exponential increase to the later part of the spontaneous depolarization that brings the surface membrane to threshold to fire an action potential (AP). Here, in single isolated intact SANC, using the phosphorylation site-specific polyclonal antibody, we show (Fig. A ) that, basal state phospholamban (PLB) phosphorylation at Thr-17, a CaMKII phosphorylation site, is over 3 times greater in SANC than in ventricular cells (VC). The CaMKII inhibitor, KN-93, but not its inactive analog, KN-92, markedly inhibits (by 80%) PLB Thr-17 phosphorylation (Fig. B ). Confocal imaging of saponin permeablized SANC, superfused in physiological solution with 150nM free Ca 2+ and 0.5mM EGTA, showed that KN-93 reduced the LCR frequency by 80% (from 5.6 ± 1.5 to 1.1 ± 0.3/1s × 100 μm) and size by 50% (from 4.0 ± 0.3 to 2.0 ± 0.3 μm). Thus, in addition to an effect on L-type Ca 2+ channels, the high basal CaMKII activation (indexed by PLB phosphorylation at Thr-17) has a major effect to determine the characteristics of spontaneous LCR’s that initiate AP’s and control normal automaticity of SANC.

scholarly journals Properties of Ca2+ sparks revealed by four-dimensional confocal imaging of cardiac muscle

2012 ◽  
Vol 139 (3) ◽  
pp. 189-207 ◽  
Author(s):  
Vyacheslav M. Shkryl ◽  
Lothar A. Blatter ◽  
Eduardo Ríos
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Rise Time ◽  
Confocal Imaging ◽  
Imaging Studies ◽  
Atrial Cells ◽  
Ventricular Cells ◽  
Release Flux ◽  
Functional Relevance ◽  
Kinetics Of

Parameters (amplitude, width, kinetics) of Ca2+ sparks imaged confocally are affected by errors when the spark source is not in focus. To identify sparks that were in focus, we used fast scanning (LSM 5 LIVE; Carl Zeiss) combined with fast piezoelectric focusing to acquire x–y images in three planes at 1-µm separation (x-y-z-t mode). In 3,000 x–y scans in each of 34 membrane-permeabilized cat atrial cardiomyocytes, 6,906 sparks were detected. 767 sparks were in focus. They had greater amplitude, but their spatial width and rise time were similar compared with all sparks recorded. Their distribution of amplitudes had a mode at ΔF/F0 = 0.7. The Ca2+ release current underlying in-focus sparks was 11 pA, requiring 20 to 30 open channels, a number at the high end of earlier estimates. Spark frequency was greater than in earlier imaging studies of permeabilized ventricular cells, suggesting a greater susceptibility to excitation, which could have functional relevance for atrial cells. Ca2+ release flux peaked earlier than the time of peak fluorescence and then decayed, consistent with significant sarcoplasmic reticulum (SR) depletion. The evolution of fluorescence and release flux were strikingly similar for in-focus sparks of different rise time (T). Spark termination involves both depletion of Ca2+ in the SR and channel closure, which may be synchronized by depletion. The observation of similar flux in sparks of different T requires either that channel closure and other termination processes be independent of the determinants of flux (including [Ca2+]SR) or that different channel clusters respond to [Ca2+]SR with different sensitivity.

Sarcoplasmic reticulum Ca2+ pump in pig coronary artery smooth muscle is regulated by a novel pathway

1996 ◽  
Vol 271 (1) ◽  
pp. C181-C187 ◽  
Author(s):  
A. K. Grover ◽  
A. Xu ◽  
S. E. Samson ◽  
N. Narayanan
Keyword(s):  
Smooth Muscle ◽  
Coronary Artery ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Phosphorylation Site ◽  
Cyclopiazonic Acid ◽  
Western Blots ◽  
Calmodulin Antagonist ◽  
Calmodulin Kinase ◽  
Kinase Phosphorylation

Coronary artery smooth muscle expresses an alternative splice (SERCA2b) of the sarcoplasmic reticulum (SR) Ca2+ pump gene SERCA2, which is also expressed in cardiac muscle (SERCA2a), but how the activity of this transporter is regulated in the coronary artery is not known. SERCA2a in the cardiac muscle can be regulated via phospholamban or, as recently reported, by a direct phosphorylation of this protein by calmodulin kinase (Xu, A., C. Hawkins, and N. Narayanan. J.Biol. Chem. 268:8394-8397, 1993). Because both SERCA2a and SERCA2b contain this calmodulin kinase phosphorylation site, we examined the effect of endogenous calmodulin kinase phosphorylation of the SR Ca2+ pump in the coronary artery. SR-enriched membranes were isolated from coronary artery smooth muscle and washed in ethylene glycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to remove bound calmodulin. When these membranes were incubated with MgATP2- in the presence of Ca2+/calmodulin, a 115-kDa protein was phosphorylated. This phosphorylated 115-kDa protein was identified as SERCA2b in Western blots and by immunoprecipitation using a SERCA2-selective antibody. Preincubating the membranes in MgATP2- in the presence of Ca2+/calmodulin stimulated the subsequent Ca2+ uptake in the presence of oxalate plus MgATP2- and azide. The stimulation of Ca2+ uptake was inhibited by including the SR Ca2+ pump inhibitors thapsigargin and cyclopiazonic acid in the Ca2+ uptake medium or by including the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide or the calmodulin kinase II peptide fragment 290-309 in the phosphorylation solution. Thus an endogenous calmodulin-dependent kinase phosphorylated SERCA2b and activated it. Phospholamban could not be detected in these membranes in Western blots. Therefore, the regulation of the SR Ca2+ pump activity in coronary artery smooth muscle may involve a direct phosphorylation of the pump protein by an endogenous calmodulin-dependent kinase.

scholarly journals Resonance Instability of Photovoltaic E-Bike Charging Stations: Control Parameters Analysis, Modeling and Experiment

2019 ◽  
Vol 9 (2) ◽  
pp. 252 ◽  
Author(s):  
Ziqian Zhang ◽  
Cihan Gercek ◽  
Herwig Renner ◽  
Angèle Reinders ◽  
Lothar Fickert
Keyword(s):  
Major Effect ◽  
Current Control ◽  
Current Loop ◽  
Control Methods ◽  
Control Parameters ◽  
Charging System ◽  
Grid Connected Inverter ◽  
The Time Domain ◽  
Charging Stations ◽  
And Control

This article presents an in-situ comparative analysis and power quality tests of a newly developed photovoltaic charging system for e-bikes. The various control methods of the inverter are modeled and a single-phase grid-connected inverter is tested under different conditions. Models are constituted for two current control methods; the proportional resonance and the synchronous rotating frames. In order to determine the influence of the control parameters, the system is analyzed analytically in the time domain as well as in the frequency domain by simulation. The tests indicated the resonance instability of the photovoltaic inverter. The passivity impedance-based stability criterion is applied in order to analyze the phenomenon of resonance instability. In conclusion, the phase-locked loop (PLL) bandwidth and control parameters of the current loop have a major effect on the output admittance of the inverter, which should be adjusted to make the system stable.

Effects of ischemia on sarcoplasmic reticulum and contractile myofilament activity in human myocardium

1993 ◽  
Vol 265 (4) ◽  
pp. H1334-H1341 ◽  
Author(s):  
G. B. Luciani ◽  
A. D'Agnolo ◽  
A. Mazzucco ◽  
V. Gallucci ◽  
G. Salviati
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Heart Surgery ◽  
Open Heart Surgery ◽  
Isometric Tension ◽  
Hill Coefficient ◽  
Calmodulin Antagonist ◽  
Contractile System ◽  
Cardiac Fiber ◽  
And Control

The effects of global ischemia on the contractile system and on sarcoplasmic reticulum (SR) function were studied by measuring the isometric tension and the SR Ca2+ release activity of chemically skinned cardiac fiber preparations from seven patients undergoing open-heart surgery. Ten minutes of ischemia caused 1) a decrease in the myofilament sensitivity to Ca2+ (expected Ca2+ concentration giving half-maximal tension; from 0.69 +/- 0.04 to 1.38 +/- 0.06 microM, n = 7) and in the cooperativity index (Hill coefficient; from 2.61 +/- 0.45 to 0.92 +/- 0.15, n = 7), 2) a decrease in myosin light chain phosphorylation, and 3) a 300% increase in the threshold caffeine concentration for SR Ca2+ efflux channel activation, with a 30% reduction in the rate of Ca2+ release by caffeine at threshold concentrations and a 23% reduction in the rate of release by 20 mM caffeine. After preincubation with 5 microM trifluoperazine, a calmodulin antagonist, the caffeine threshold of ischemic and control cardiac muscle became comparable. Most changes were reversed by reperfusion, while the caffeine threshold was still two times greater than control. These results indicate that ischemia caused alterations of the cardiac muscle contractile apparatus and the SR that were reversed only after reperfusion.

Glucose absorption by in vitro perfused colon of the fetal rat

1983 ◽  
Vol 245 (3) ◽  
pp. G424-G430 ◽  
Author(s):  
G. D. Potter ◽  
K. L. Schmidt ◽  
R. Lester
Keyword(s):  
Small Bowel ◽  
Average Molecular Weight ◽  
Glucose Absorption ◽  
Physiological Solution ◽  
Rat Colon ◽  
Transmission Electron ◽  
Fetal Rat ◽  
Luminal Perfusion ◽  
And Control

The anatomic configuration of fetal rat colon resembles that of the small bowel. Accordingly, glucose and amino acid absorption were measured in order to see whether the fetal rat colon resembled the small bowel functionally. In vitro luminal perfusion of the fetal rat colon at 20 days of gestation was employed to measure the rate of glucose and L-alanine absorption and the unidirectional flux rates of 3-O-methylglucose (3-O-MG). The colon was mounted between pipettes in a heated oxygenated bath and perfused with the solute to be studied dissolved in buffered physiological solution and polyethylene glycol with average molecular weight of 4,000 (PEG) as a nonabsorbable marker substance. The PEG was not transported and did not diffuse across fetal colon. Scanning and transmission electron microscopy of perfused and control colon showed the presence of villi and the preservation of mucosal anatomy during perfusion. Glucose was absorbed at 173 +/- 16 mumol . h-1 . g-1 (8) and absorption was abolished in Na-free solution. 3-O-MG flux was 40 +/- 7 mumol . h-1 . g-1 (8) from lumen to bath and 7 +/- 1 mumol . h-1 . g-1 (8) from bath to lumen. L-Alanine flux was 130 +/- 15 mumol . h-1 . g-1 (8) from lumen to bath and 18 +/- 4 mumol . h-1 . g-1 (5) from bath to lumen, and the lumen-to-bath flux was only partially abolished by Na-free solutions.

A discrete Na-Ca exchange-dependent Ca compartment in rat ventricular cells: exchange and localization

1992 ◽  
Vol 262 (5) ◽  
pp. C1149-C1153 ◽  
Author(s):  
G. A. Langer ◽  
T. L. Rich
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Intracellular Calcium ◽  
Binding Sites ◽  
Rat Heart ◽  
Half Time ◽  
Adult Rat ◽  
Ventricular Cells ◽  
Intracellular Ca ◽  
Rapid Perfusion ◽  
Limited Exchange

Application of a new rapid perfusion (up to 4.8 ml/s) technique to 45Ca-labeled ventricular cells from adult rat heart has defined a discrete intracellular calcium (Ca) compartment with the following characteristics: 1) its exchange is absolutely dependent on operation of the Na-Ca exchanger, i.e., its isotopic content remains constant during washout in the absence of Na and Ca and is released only upon addition of Na and Ca to the perfusate. 2) At an extracellular Ca concentration of 1.0 mM it contains 350 mumol/kg dry wt cells and exchanges with half time of 650 ms. Ca flux from the compartment is 385 mumol.kg dry wt-1.s-1 or 20% of the total nonperfusion limited flux from the cells. 3) Its content is decreased 19% by 10 mM caffeine but not diminished by exposure of the cells to 10(-6) M ryanodine and not accessible to lanthanum (La) displacement. 4) Only limited exchange occurs when only Na or Ca is present and exchange is virtually eliminated by substitution of extracellular Li for extracellular Na. 5) Replacement of Na and Ca to the perfusate after various periods of removal produces no contraction (despite immediate Ca release from the cell). The results define a discrete intracellular Ca compartment which exchanges only via the Na-Ca exchanger. It is not La accessible, not in the ryanodine- or caffeine-sensitive portions of the sarcoplasmic reticulum, not in the mitochondria nor at the myofilaments, but may reside at inner sarcolemmal leaflet binding sites.

scholarly journals A Longitudinal View of Look at the Effectiveness of Elicited Imitation with Computer Assisted Pronunciation Training (CAPT)

2016 ◽  
Vol 4 (1) ◽  
pp. 159
Author(s):  
Liwei Hsu
Keyword(s):  
Growth Curve ◽  
Major Effect ◽  
Control Group ◽  
Computer Assisted ◽  
Growth Curve Analysis ◽  
Elicited Imitation ◽  
Significant Difference ◽  
Longitudinal View ◽  
Group Interviews ◽  
And Control

<p>It is the aim for most EFL learners to have a clear pronunciation in English; however, pronunciation training has always been a challenge for EFL teachers and learners alike. The advent of Computer Assisted Pronunciation Training (CAPT) seems to be the solution to this problem. This longitudinal study adopted a latent growth curve to describe 30 EFL learner’s (N = 30) development of imitated pronunciation in English as well as their satisfaction regarding CAPT. These 30 participants were randomly assigned to the experimental group (N = 18) and control group (N = 12). There were no significant differences among the participants in their pronunciation of English or attitudes toward CAPT at the beginning of this study. After 16 months of training, the growth curve analysis showed that participants in the CAPT group made significantly greater development in English pronunciation, and they were more satisfied with the CAPT. The large effect size indicated that the grouping was the major effect that led to a significant difference in satisfaction. Moreover, the qualitative data derived from focus-group interviews confirmed the benefits of CAPT in participant’s pronunciation training. These findings suggest that EFL learner’s opportunities to conduct elicited imitation with the help of ASR-CAPT will be helpful for their development of imitated pronunciation in English and increase their satisfaction of it, which is a key aspect in the effectiveness of pronunciation training. </p>

Altered electrical response to caffeine exposure in hypertrophied rat myocardium

1989 ◽  
Vol 67 (12) ◽  
pp. 1471-1479 ◽  
Author(s):  
C. Thollon ◽  
P. Kreher
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Action Potential ◽  
Calcium Release ◽  
Pressure Overload ◽  
Coronary Artery Ligation ◽  
Aortocaval Fistula ◽  
Aortic Constriction ◽  
Artery Ligation ◽  
And Control ◽  
Later Phase

We investigated the electrophysiological effects of cardiac hypertrophy induced by different experimental models. Comparison of the action potentials of hypertrophied and control rat hearts reveals a pronounced prolongation of the action potential for all types of hypertrophy. This prolongation affects the entire repolarization phase of the action potential 8 days after severe aortic constriction, after 8 days of isoproterenol treatment (5 mg/kg per day), and 3 months after an aortocaval fistula. The electrical changes associated with myocardial hypertrophy induced by pressure overload (aortic constriction) were compared with those resulting from volume overload (aortocaval fistula). Our results show that action potential alterations depend on the nature, duration, and severity of the work load. Thus, pressure overload is more potent to induce these modifications. In the hearts subjected to pressure overload, action potential alterations appear more rapidly and are more marked for the same degree of hypertrophy than those of the volume-hypertrophied myocardium. Furthermore, such data also demonstrate that the early alteration of the action potential during the development of compensatory hypertrophy is a prolongation of the later phase of repolarization (phase 3), without prolongation of the other repolarization phases (1 and 2). This change appears 3 days after aortic constriction, 1 month after coronary artery ligation (in the healthy part of the left ventricle), and 1 month after an aortocaval fistula. In the rat heart, the ionic currents underlying this later phase of repolarization are known to be dependent on the increase of intracellular free calcium during activity. Since this elevation of myoplasmic calcium results from calcium release from the sarcoplasmic reticulum, we compared the effects of caffeine (a substance known to act on the sarcoplasmic reticulum) on the electrical events of hypertrophied and control hearts. Caffeine has a different qualitative effect in hypertrophied and control hearts. The results suggest that hypertrophy should be due to increased calcium release from the sarcoplasmic reticulum related to increased phosphoinositide hydrolysis and therefore that the prolongation of the action potential duration (phase 3) may be the result of an increase of the Na–Ca exchange current or of a specific suppression of the outward K+ current.Key words: aortic stenosis, isoproterenol treatment, coronary artery ligation, aortocaval fistula, action potential, caffeine.

Effects of Volatile Anesthetics on Sarcolemmal Calcium Transport and Sarcoplasmic Reticulum Calcium Content in Isolated Myocytes

2002 ◽  
Vol 96 (6) ◽  
pp. 1457-1464 ◽  
Author(s):  
James D. Hannon ◽  
Mark J. Cody
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Adenosine Triphosphatase ◽  
Surface Membrane ◽  
State Level ◽  
Calcium Content ◽  
Right Ventricular Free Wall ◽  
Acetoxymethyl Ester ◽  
Ionic Substitution ◽  
Rate Of Decline ◽  
The Right

Background The surface membrane Ca(2+)-adenosine triphosphatase and Na(+)-Ca(2+) exchanger transport Ca(2+) out of the ventricular myocyte, competing for cytosolic Ca(2+) with the Ca(2+)-adenosine triphosphatase located in the sarcoplasmic reticulum. In this study the authors examined the effects of halothane, isoflurane, and sevoflurane on Ca(2+) extrusion from the cell and sarcoplasmic reticulum Ca(2+) content. Methods Single myocytes from the right ventricular free wall of adult male ferret hearts were isolated, loaded with the acetoxymethyl ester of the fluorescent Ca(2+) indicator fluo-3, and electrically stimulated at 0.25 Hz to reach a steady state level of intracellular Ca(2+) stores. The effects of halothane, isoflurane, and sevoflurane (1 minimum alveolar concentration) on the peak and rate of decline of the Ca(2+) transient induced by 10 mm caffeine were examined. The peak was used as an index of sarcoplasmic reticulum Ca(2+) content, and the rate of decline was used to monitor Ca(2+) extrusion from the cell. Results During control conditions, halothane reduced the Ca(2+) content of the sarcoplasmic reticulum, isoflurane maintained it, and sevoflurane caused it to increase. Halothane did not affect Ca(2+) extrusion from the cell, but both isoflurane and sevoflurane inhibited it. When Na(+)-Ca(2+) exchange was inhibited by ionic substitution, isoflurane and sevoflurane still reduced the rate of Ca(2+) efflux from the cell. However, when the sarcolemmal Ca(2+)-adenosine triphosphatase was inhibited by carboxyeosin, isoflurane and sevoflurane had no effect on Ca(2+) efflux. Conclusions These results suggest that isoflurane and sevoflurane inhibit Ca(2+) transport from the cell via the sarcolemmal Ca(2+)-adenosine triphosphatase. This effect seems to counteract the decrease in Ca(2+) influx through sarcolemmal L-type Ca(2+) channels and maintains sarcoplasmic reticulum Ca(2+) stores.

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