BAY K 8644 modifies Ca2+cross signaling between DHP and ryanodine receptors in rat ventricular myocytes

1999 ◽  
Vol 276 (4) ◽  
pp. H1178-H1189 ◽  
Author(s):  
Satomi Adachi-Akahane ◽  
Lars Cleemann ◽  
Martin Morad
Keyword(s):  
Amplification Factor ◽  
Ventricular Myocytes ◽  
Ryanodine Receptors ◽  
Bay K 8644 ◽  
Local Exchange ◽  
Rat Ventricular Myocytes ◽  
Channel Current ◽  
Dependent Inactivation ◽  
Intracellular Ca ◽  
Kinetics Of

The amplification factor of dihydropyridine (DHP)/ryanodine receptors was defined as the amount of Ca2+ released from the sarcoplasmic reticulum (SR) relative to the influx of Ca2+ through L-type Ca2+ channels in rat ventricular myocytes. The amplification factor showed steep voltage dependence at potentials negative to −10 mV but was less dependent on voltage at potentials positive to this value. In cells dialyzed with 0.2 mM cAMP in addition to 2 mM fura 2, the Ca2+-channel agonist (−)-BAY K 8644 enhanced Ca2+-channel current ( I Ca), shifted the activation curve by −10 mV, and significantly delayed its inactivation. Surprisingly, BAY K 8644 reduced the amplification factor by 50% at all potentials, even though the caffeine-releasable Ca2+ stores were mostly intact at holding potentials of −90 mV. In contrast, brief elevation of extracellular Ca2+ activity from 2 to 10 mM enhanced both I Ca and intracellular Ca2+ transients in the absence or presence of BAY K 8644 but had no significant effect on the amplification factor. BAY K 8644 abolished the direct dependence of the rate of inactivation of I Ca on the release of Ca2+ from the SR. These findings suggest that the gain of the Ca2+-induced Ca2+ release in cardiac myocytes is regulated by the gating kinetics of cardiac L-type Ca2+ channels via local exchange of Ca2+ signals between DHP and ryanodine receptors and that BAY K 8644 suppresses the amplification factor through attenuation of the Ca2+-dependent inactivation of Ca2+ channels.

scholarly journals Warmer, faster, stronger: Ca2+ cycling in avian myocardium

2020 ◽  
Vol 223 (19) ◽  
pp. jeb228205
Author(s):  
Tatiana S. Filatova ◽  
Denis V. Abramochkin ◽  
Holly A. Shiels
Keyword(s):  
Cross Talk ◽  
High Efficiency ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Ryanodine Receptors ◽  
Atrial Cells ◽  
Ventricular Cells ◽  
Dependent Inactivation ◽  
Intracellular Ca ◽  
Mammalian Myocardium

ABSTRACTBirds occupy a unique position in the evolution of cardiac design. Their hearts are capable of cardiac performance on par with, or exceeding that of mammals, and yet the structure of their cardiomyocytes resembles those of reptiles. It has been suggested that birds use intracellular Ca2+ stored within the sarcoplasmic reticulum (SR) to power contractile function, but neither SR Ca2+ content nor the cross-talk between channels underlying Ca2+-induced Ca2+ release (CICR) have been studied in adult birds. Here we used voltage clamp to investigate the Ca2+ storage and refilling capacities of the SR and the degree of trans-sarcolemmal and intracellular Ca2+ channel interplay in freshly isolated atrial and ventricular myocytes from the heart of the Japanese quail (Coturnix japonica). A trans-sarcolemmal Ca2+ current (ICa) was detectable in both quail atrial and ventricular myocytes, and was mediated only by L-type Ca2+ channels. The peak density of ICa was larger in ventricular cells than in atrial cells, and exceeded that reported for mammalian myocardium recorded under similar conditions. Steady-state SR Ca2+ content of quail myocardium was also larger than that reported for mammals, and reached 750.6±128.2 μmol l−1 in atrial cells and 423.3±47.2 μmol l−1 in ventricular cells at 24°C. We observed SR Ca2+-dependent inactivation of ICa in ventricular myocytes, indicating cross-talk between sarcolemmal Ca2+ channels and ryanodine receptors in the SR. However, this phenomenon was not observed in atrial myocytes. Taken together, these findings help to explain the high-efficiency avian myocyte excitation–contraction coupling with regard to their reptilian-like cellular ultrastructure.

A model of graded calcium release and L-type Ca2+ channel inactivation in cardiac muscle

2004 ◽  
Vol 286 (3) ◽  
pp. H1154-H1169 ◽  
Author(s):  
Vladimir E. Bondarenko ◽  
Glenna C. L. Bett ◽  
Randall L. Rasmusson
Keyword(s):  
Molecular Mechanisms ◽  
Calcium Release ◽  
Ventricular Myocytes ◽  
Ryanodine Receptors ◽  
Quantitative Description ◽  
Channel Current ◽  
Channel Inactivation ◽  
Transmembrane Voltage ◽  
Intracellular Ca ◽  
Junctional Sarcoplasmic Reticulum

We have developed a model of Ca2+ handling in ferret ventricular myocytes. This model includes a novel L-type Ca2+ channel, detailed intracellular Ca2+ movements, and graded Ca2+-induced Ca2+ release (CICR). The model successfully reproduces data from voltage-clamp experiments, including voltage- and time-dependent changes in intracellular Ca2+ concentration ([Ca2+]i), L-type Ca2+ channel current ( ICaL) inactivation and recovery kinetics, and Ca2+ sparks. The development of graded CICR is critically dependent on spatial heterogeneity and the physical arrangement of calcium channels in opposition to ryanodine-sensitive release channels. The model contains spatially distinct subsystems representing the subsarcolemmal regions where the junctional sarcoplasmic reticulum (SR) abuts the T-tubular membrane and where the L-type Ca2+ channels and SR ryanodine receptors (RyRs) are localized. There are eight different types of subsystems in our model, with between one and eight L-type Ca2+ channels distributed binomially. This model exhibits graded CICR and provides a quantitative description of Ca2+ dynamics not requiring Monte-Carlo simulations. Activation of RyRs and release of Ca2+ from the SR depend critically on Ca2+ entry through L-type Ca2+ channels. In turn, Ca2+ channel inactivation is critically dependent on the release of stored intracellular Ca2+. Inactivation of ICaL depends on both transmembrane voltage and local [Ca2+]i near the channel, which results in distinctive inactivation properties. The molecular mechanisms underlying many ICaL gating properties are unclear, but [Ca2+]i dynamics clearly play a fundamental role.

scholarly journals Cross-signaling between L-type Ca2+ channels and ryanodine receptors in rat ventricular myocytes.

1996 ◽  
Vol 108 (5) ◽  
pp. 435-454 ◽  
Author(s):  
S Adachi-Akahane ◽  
L Cleemann ◽  
M Morad
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Ryanodine Receptors ◽  
Inactivation Kinetics ◽  
Rat Ventricular Myocytes ◽  
Fura 2 ◽  
High Concentrations ◽  
A Charge ◽  
Indicator Dye ◽  
Kinetics Of

Calcium-mediated cross-signaling between the dihydropyridine (DHP) receptor, ryanodine receptor, and Na(+)-Ca2+ exchanger was examined in single rat ventricular myocytes where the diffusion distance of Ca2+ was limited to < 50 nm by dialysis with high concentrations of Ca2+ buffers. Dialysis of the cell with 2 mM Ca(2+)- indicator dye, Fura-2, or 2 mM Fura-2 plus 14 mM EGTA decreased the magnitude of ICa-triggered intracellular Ca2+ transients (Cai-transients) from 500 to 20-100 nM and completely abolished contraction, even though the amount of Ca2+ released from the sarcoplasmic reticulum remained constant (approximately 140 microM). Inactivation kinetics of ICa in highly Ca(2+)-buffered cells was retarded when Ca2+ stores of the sarcoplasmic reticulum (SR) were depleted by caffeine applied 500 ms before activation of ICa, while inactivation was accelerated if caffeine-induced release coincided with the activation of ICa. Quantitative analysis of these data indicate that the rate of inactivation of ICa was linearly related to SR Ca(2+)-release and reduced by > 67% when release was absent. Thapsigargin, abolishing SR release, suppressed the effect of caffeine on the inactivation kinetics of ICa. Caffeine-triggered Ca(2+)-release, in the absence of Ca2+ entry through the Ca2+ channel (using Ba2+ as a charge carrier), caused rapid inactivation of the slowly decaying Ba2+ current. Since Ba2+ does not release Ca2+ but binds to Fura-2, it was possible to calibrate the fluorescence signals in terms of equivalent cation charge. Using this procedure, the amplification factor of ICa-induced Ca2+ release was found to be 17.6 +/- 1.1 (n = 4). The Na(+)-Ca2+ exchange current, activated by caffeine-induced Ca2+ release, was measured consistently in myocytes dialyzed with 0.2 but not with 2 mM Fura-2. Our results quantify Ca2+ signaling in cardiomyocytes and suggest the existence of a Ca2+ microdomain which includes the DHP/ ryanodine receptors complex, but excludes the Na(+)-Ca2+ exchanger. This microdomain appears to be fairly inaccessible to high concentrations of Ca2+ buffers.

Fluid pressure modulates L-type Ca2+ channel via enhancement of Ca2+-induced Ca2+ release in rat ventricular myocytes

2008 ◽  
Vol 294 (4) ◽  
pp. C966-C976 ◽  
Author(s):  
Sunwoo Lee ◽  
Joon-Chul Kim ◽  
Yuhua Li ◽  
Min-Jeong Son ◽  
Sun-Hee Woo
Keyword(s):  
Ventricular Myocytes ◽  
Fluid Pressure ◽  
Inhibitory Effect ◽  
Cellular Mechanism ◽  
Confocal Imaging ◽  
Rat Ventricular Myocytes ◽  
Whole Cell Patch Clamp ◽  
Current Voltage ◽  
Intracellular Ca ◽  
High Concentrations

This study examines whether fluid pressure (FP) modulates the L-type Ca2+ channel in cardiomyocytes and investigates the underlying cellular mechanism(s) involved. A flow of pressurized (∼16 dyn/cm2) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes using a microperfusion method. The Ca2+ current ( ICa) and cytosolic Ca2+ signals were measured using a whole cell patch-clamp and confocal imaging, respectively. It was found that the FP reversibly suppressed ICa (by 25%) without altering the current-voltage relationships, and it accelerated the inactivation of ICa. The level of ICa suppression by FP depended on the level and duration of pressure. The Ba2+ current through the Ca2+ channel was only slightly decreased by the FP (5%), suggesting an indirect inhibition of the Ca2+ channel during FP stimulation. The cytosolic Ca2+ transients and the basal Ca2+ in field-stimulated ventricular myocytes were significantly increased by the FP. The effects of the FP on the ICa and on the Ca2+ transient were resistant to the stretch-activated channel inhibitors, GsMTx-4 and streptomycin. Dialysis of myocytes with high concentrations of BAPTA, the Ca2+ buffer, eliminated the FP-induced acceleration of ICa inactivation and reduced the inhibitory effect of the FP on ICa by ≈80%. Ryanodine and thapsigargin, abolishing sarcoplasmic reticulum Ca2+ release, eliminated the accelerating effect of FP on the ICa inactivation, and they reduced the inhibitory effect of FP on the ICa. These results suggest that the fluid pressure indirectly suppresses the Ca2+ channel by enhancing the Ca2+-induced intracellular Ca2+ release in rat ventricular myocytes.

Changes of action potential and L-type calcium channel current of Sprague–Dawley rat ventricular myocytes by different amlodipine isomers

2008 ◽  
Vol 86 (9) ◽  
pp. 620-625 ◽  
Author(s):  
Ru-xing Wang ◽  
Wen-ping Jiang
Keyword(s):  
Steady State ◽  
Action Potential ◽  
Calcium Channel ◽  
Ventricular Myocytes ◽  
Channel Blockers ◽  
Sprague Dawley ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Channel Current ◽  
Steady State Inactivation

To investigate the effects of S- and R-amlodipine (Aml) on action potential (AP) and L-type calcium channel current (ICa-L), the whole-cell patch-clamp technique was used on rat ventricular myocytes to record AP, ICa-L, peak currents, steady-state activation currents, steady-state inactivation currents, and recovery currents from inactivation with S-Aml and R-Aml at various concentrations. Increasing concentrations of S-Aml gradually shortened AP durations (APDs). At concentrations of 0.1, 0.5, 1, 5, and 10 μmol/L, S-Aml blocked 1.5% ± 0.2%, 25.4% ± 5.3%, 65.2% ± 7.3%, 78.4% ± 8.1%, and 94.2% ± 5.0% of ICa-L, respectively (p < 0.05), and the half-inhibited concentration was 0.62 ± 0.12 µmol/L. Current–voltage curves were shifted upward; steady-state activation and inactivation curves were shifted to the left. At these concentrations of S-Aml, the half-activation voltages were –16.01 ± 1.65, –17.61 ± 1.60, –20.17 ± 1.46, –21.87 ± 1.69, and –24.09 ± 1.87 mV, respectively, and the slope factors were increased (p < 0.05). The half-inactivation voltages were –27.16 ± 4.48, –28.69 ± 4.52, –31.19 ± 4.17, –32.63 ± 4.34, and –35.16 ± 4.46 mV, respectively, and the slope factors were increased (p < 0.05). The recovery times from inactivation of S-Aml were prolonged (p < 0.05). In contrast, R-Aml had no effect on AP and ICa-L (p > 0.05) at the concentrations tested. Thus, only S-Aml has calcium channel blockade activity, whereas R-Aml has none of the pharmacologic actions associated with calcium channel blockers.

S4-4 Camkii modulates intracellular Ca regulation and ICa in rat ventricular myocytes during acidosis

2002 ◽  
Vol 34 (10) ◽  
pp. A11
Author(s):  
Kimiaki Komukai ◽  
Caroline Pascarel ◽  
Fabien Brette ◽  
Clive H. Orchard ◽  
Seibu Mochizuki
Keyword(s):  
Ventricular Myocytes ◽  
Rat Ventricular Myocytes ◽  
Intracellular Ca

CaMKII-dependent reactivation of SR Ca2+ uptake and contractile recovery during intracellular acidosis

2002 ◽  
Vol 283 (1) ◽  
pp. H193-H203 ◽  
Author(s):  
Noriyuki Nomura ◽  
Hiroshi Satoh ◽  
Hajime Terada ◽  
Masaki Matsunaga ◽  
Hiroshi Watanabe ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Selective Inhibitor ◽  
Intracellular Acidosis ◽  
Rat Ventricular Myocytes ◽  
Calmodulin Kinase ◽  
Intracellular Ca ◽  
Contractile Recovery ◽  
Contractile Performance

In hearts, intracellular acidosis disturbs contractile performance by decreasing myofibrillar Ca2+ response, but contraction recovers at prolonged acidosis. We examined the mechanism and physiological implication of the contractile recovery during acidosis in rat ventricular myocytes. During the initial 4 min of acidosis, the twitch cell shortening decreased from 2.3 ± 0.3% of diastolic length to 0.2 ± 0.1% (means ± SE, P < 0.05, n = 14), but in nine of these cells, contractile function spontaneously recovered to 1.5 ± 0.3% at 10 min ( P < 0.05 vs. that at 4 min). During the depression phase, both the diastolic intracellular Ca2+ concentration ([Ca2+]i) and Ca2+ transient (CaT) amplitude increased, and the twitch [Ca2+]i decline prolonged significantly ( P < 0.05). In the cells that recovered, a further increase in CaT amplitude and a reacceleration of twitch [Ca2+]i decline were observed. The increase in diastolic [Ca2+]i was less extensive than the increase in the cells that did not recover ( n = 5). Blockade of sarcoplasmic reticulum (SR) function by ryanodine (10 μM) and thapsigargin (1 μM) or a selective inhibitor of Ca2+-calmodulin kinase II, 2-[ N- (2-hydroxyethyl)- N-(4-methoxybenzenesulfonyl)] amino- N-(4-chlorocinnamyl)- N-methyl benzylamine (1 μM) completely abolished the reacceleration of twitch [Ca2+]i decline and almost eliminated the contractile recovery. We concluded that during prolonged acidosis, Ca2+-calmodulin kinase II-dependent reactivation of SR Ca2+ uptake could increase SR Ca2+ content and CaT amplitude. This recovery can compensate for the decreased myofibrillar Ca2+ response, but may also cause Ca2+ overload after returning to physiological pHi.

CaM kinase augments cardiac L-type Ca2+ current: a cellular mechanism for long Q-T arrhythmias

1999 ◽  
Vol 276 (6) ◽  
pp. H2168-H2178 ◽  
Author(s):  
Yuejin Wu ◽  
Leigh B. MacMillan ◽  
R. Blair McNeill ◽  
Roger J. Colbran ◽  
Mark E. Anderson
Keyword(s):  
Ventricular Myocytes ◽  
Ryanodine Receptors ◽  
Cam Kinase ◽  
Early Afterdepolarizations ◽  
Ultrastructural Studies ◽  
Intracellular Ca ◽  
Dependent Protein ◽  
T Tubules ◽  
Rabbit Ventricular Myocytes

Early afterdepolarizations (EAD) caused by L-type Ca2+ current ( I Ca,L) are thought to initiate long Q-T arrhythmias, but the role of intracellular Ca2+ in these arrhythmias is controversial. Rabbit ventricular myocytes were stimulated with a prolonged EAD-containing action potential-clamp waveform to investigate the role of Ca2+/calmodulin-dependent protein kinase II (CaM kinase) in I Ca,L during repolarization. I Ca,L was initially augmented, and augmentation was dependent on Ca2+ from the sarcoplasmic reticulum because the augmentation was prevented by ryanodine or thapsigargin. I Ca,Laugmentation was also dependent on CaM kinase, because it was prevented by dialysis with the inhibitor peptide AC3-I and reconstituted by exogenous constitutively active CaM kinase when Ba2+ was substituted for bath Ca2+. Ultrastructural studies confirmed that endogenous CaM kinase, L-type Ca2+ channels, and ryanodine receptors colocalized near T tubules. EAD induction was significantly reduced in current-clamped cells dialyzed with AC3-I (4/15) compared with cells dialyzed with an inactive control peptide (11/15, P = 0.013). These findings support the hypothesis that EADs are facilitated by CaM kinase.

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