Mechanism of enhancement of slow delayed rectifier current by extracellular sulfhydryl modification

1997 ◽  
Vol 273 (1) ◽  
pp. H208-H219 ◽  
Author(s):  
J. A. Yao ◽  
M. Jiang ◽  
G. N. Tseng
Keyword(s):  
Transmembrane Domain ◽  
Ventricular Myocytes ◽  
Current Model ◽  
The Other ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Sh Group ◽  
Intracellular Ca ◽  
Sulfhydryl Modification

To explore the role of sulfhydryl (SH) groups in the function of cardiac slow delayed rectifier channels, we tested the effects of extracellular thimerosal (TMS, a hydrophilic SH modifier) on slow delayed rectifier current (IKs) induced by human IsK (hIsK) in oocytes and on the native IKs in canine ventricular myocytes. TMS (25 or 50 microM) had similar effects on the two currents: current amplitude increased, and there was an acceleration of activation and a slowing of deactivation. These effects showed little or no reversal after washout of TMS. The effects did not depend on intracellular Ca release or protein kinase activities but could be suppressed by dithiothreitol pretreatment. According to the current model of transmembrane topology, there is no cystein in the extracellular domain of hIsK. A likely candidate for TMS modification is the SH group on another subunit in oocyte cell membrane that interacts with IsK to form a functional channel. To explore the domain of hIsK involved in the interaction, extracellular serines of hIsK were mutated to cysteines at three locations: S37C (close to the transmembrane domain), S4C (close to the NH2-terminus), and S28C (in between). S37C and S28C mutations did not affect channel properties or hIsK response to TMS. On the other hand, S4C mutation reduced current expression even when S4C cRNA was injected at a quantity 50-fold higher than that of the other three proteins. Importantly, the response to TMS was markedly reduced in S4C compared with the other three proteins. Therefore, the NH2-terminus of hIsK may be involved in hIsK interaction with the SH-bearing subunit, and this interaction modulates slow delayed rectifier channel function.

Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization

2000 ◽  
Vol 278 (3) ◽  
pp. H806-H817 ◽  
Author(s):  
Gary A. Gintant
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Inward Rectifier ◽  
Ventricular Repolarization ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Delayed Rectifier Current ◽  
Recovery From Inactivation ◽  
Voltage Dependent

Although inactivation of the rapidly activating delayed rectifier current ( I Kr) limits outward current on depolarization, the role of I Kr (and recovery from inactivation) during repolarization is uncertain. To characterize I Krduring ventricular repolarization (and compare with the inward rectifier current, I K1), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I Kr was minimal at plateau potentials but transiently increased during repolarizing ramps. The I Kr transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I Kr transient terminating the plateau. Although peak I Kr transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current ( I K1) density during repolarization was dispersed, whereas potentials characterizing I K1 defined a narrower (more negative) voltage range. In summary, rapidly activating I Kr provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I Kr provides a novel means for modulating the contribution of this current during repolarization.

Temperature-dependent expression of sarcolemmal K+ currents in rainbow trout atrial and ventricular myocytes

2002 ◽  
Vol 282 (4) ◽  
pp. R1191-R1199 ◽  
Author(s):  
Matti Vornanen ◽  
Ari Ryökkynen ◽  
Antti Nurmi
Keyword(s):  
Rainbow Trout ◽  
Cardiac Myocytes ◽  
Molecular Mechanisms ◽  
Ventricular Myocytes ◽  
Cardiac Contractility ◽  
Temperature Acclimation ◽  
Delayed Rectifier ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Delayed Rectifier Current ◽  
Ventricular Cells

Temperature has a strong influence on the excitability and the contractility of the ectothermic heart that can be alleviated in some species by temperature acclimation. The molecular mechanisms involved in the temperature-induced improvement of cardiac contractility and excitability are, however, still poorly known. The present study examines the role of sarcolemmal K+ currents from rainbow trout ( Oncorhynchus mykiss) cardiac myocytes after thermal acclimation. The two major K+ conductances of the rainbow trout cardiac myocytes were identified as the Ba2+-sensitive background inward rectifier current ( I K1) and the E-4031-sensitive delayed rectifier current ( I Kr). In atrial cells, the density of I K1 is very low and the density of I Kr is remarkably high. The opposite is true for ventricular cells. Acclimation to cold (4°C) modified the two K+ currents in opposite ways. Acclimation to cold increases the density of I Kr and depresses the density of I K1. These changes in repolarizing K+ currents alter the shape of the action potential, which is much shorter in cold-acclimated than warm-acclimated (17°C) trout. These results provide the first concrete evidence that K+channels of trout cardiac myocytes are adaptable units that provide means to regulate cardiac excitability and contractility as a function of temperature.

scholarly journals The calcium stored in the sarcoplasmic reticulum acts as a safety mechanism in rainbow trout heart

2014 ◽  
Vol 307 (12) ◽  
pp. R1493-R1501 ◽  
Author(s):  
Caroline Cros ◽  
Laurent Sallé ◽  
Daniel E. Warren ◽  
Holly A. Shiels ◽  
Fabien Brette
Keyword(s):  
Rainbow Trout ◽  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Adrenergic Stimulation ◽  
Relative Contribution ◽  
Safety Mechanism ◽  
Rapid Changes ◽  
Intracellular Ca ◽  
As Stress

Cardiomyocyte contraction depends on rapid changes in intracellular Ca2+. In mammals, Ca2+ influx as L-type Ca2+ current ( ICa) triggers the release of Ca2+ from sarcoplasmic reticulum (SR) and Ca2+-induced Ca2+ release (CICR) is critical for excitation-contraction coupling. In fish, the relative contribution of external and internal Ca2+ is unclear. Here, we characterized the role of ICa to trigger SR Ca2+ release in rainbow trout ventricular myocytes using ICa regulation by Ca2+ as an index of CICR. ICa was recorded with a slow (EGTA) or fast (BAPTA) Ca2+ chelator in control and isoproterenol conditions. In the absence of β-adrenergic stimulation, the rate of ICa inactivation was not significantly different in EGTA and BAPTA (27.1 ± 1.8 vs. 30.3 ± 2.4 ms), whereas with isoproterenol (1 μM), inactivation was significantly faster with EGTA (11.6 ± 1.7 vs. 27.3 ± 1.6 ms). When barium was the charge carrier, inactivation was significantly slower in both conditions (61.9 ± 6.1 vs. 68.0 ± 8.7 ms, control, isoproterenol). Quantification revealed that without isoproterenol, only 39% of ICa inactivation was due to Ca2+, while with isoproterenol, inactivation was Ca2+-dependent (∼65%) and highly reliant on SR Ca2+ (∼46%). Thus, SR Ca2+ is not released in basal conditions, and ICa is the main trigger of contraction, whereas during a stress response, SR Ca2+ is an important source of cytosolic Ca2+. This was not attributed to differences in SR Ca2+ load because caffeine-induced transients were not different in both conditions. Therefore, Ca2+ stored in SR of trout cardiomyocytes may act as a safety mechanism, allowing greater contraction when higher contractility is required, such as stress or exercise.

Postnatal development has a marked effect on ventricular repolarization in mice

2007 ◽  
Vol 293 (4) ◽  
pp. H2168-H2177 ◽  
Author(s):  
Scott A. Grandy ◽  
Véronique Trépanier-Boulay ◽  
Céline Fiset
Keyword(s):  
Postnatal Development ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Ventricular Repolarization ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Cd1 Mice ◽  
The Individual ◽  
Immature Heart

To better understand the mechanisms that underlie cardiac repolarization abnormalities in the immature heart, this study characterized and compared K+ currents in mouse ventricular myocytes from day 1, day 7, day 20, and adult CD1 mice to determine the effects of postnatal development on ventricular repolarization. Current- and patch-clamp techniques were used to examine action potentials and the K+ currents underlying repolarization in isolated myocytes. RT-PCR was used to quantify mRNA expression for the K+ channels of interest. This study found that action potential duration (APD) decreased as age increased, with the shortest APDs observed in adult myocytes. This study also showed that K+ currents and the mRNA relative abundance for the various K+ channels were significantly greater in adult myocytes compared with day 1 myocytes. Examination of the individual components of total K+ current revealed that the inward rectifier K+ current ( IK1) developed by day 7, both the Ca2+-independent transient outward current ( Ito) and the steady-state outward K+ current ( Iss) developed by day 20, and the ultrarapid delayed rectifier K+ current ( IKur) did not fully develop until the mouse reached maturity. Interestingly, the increase in IKur was not associated with a decrease in APD. Comparison of atrial and ventricular K+ currents showed that Ito and IKur density were significantly greater in day 7, day 20, and adult myocytes compared with age-matched atrial cells. Overall, it appears that, in mouse ventricle, developmental changes in APD are likely attributable to increases in Ito, Iss, and IK1, whereas the role of IKur during postnatal development appears to be less critical to APD.

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.

The functional role of cardiac T-tubules explored in a model of rat ventricular myocytes

2006 ◽  
Vol 364 (1842) ◽  
pp. 1187-1206 ◽  
Author(s):  
Michal Pásek ◽  
Jiři Šimurda ◽  
Georges Christé
Keyword(s):  
Ventricular Myocytes ◽  
Contractile Activity ◽  
Tubular Lumen ◽  
Current Clamp Mode ◽  
Intracellular Ca ◽  
Ionic Changes ◽  
Access Resistance ◽  
T Tubules ◽  
Tubular Membranes

The morphology of the cardiac transverse-axial tubular system (TATS) has been known for decades, but its function has received little attention. To explore the possible role of this system in the physiological modulation of electrical and contractile activity, we have developed a mathematical model of rat ventricular cardiomyocytes in which the TATS is described as a single compartment. The geometrical characteristics of the TATS, the biophysical characteristics of ion transporters and their distribution between surface and tubular membranes were based on available experimental data. Biophysically realistic values of mean access resistance to the tubular lumen and time constants for ion exchange with the bulk extracellular solution were included. The fraction of membrane in the TATS was set to 56%. The action potentials initiated in current-clamp mode are accompanied by transient K + accumulation and transient Ca 2+ depletion in the TATS lumen. The amplitude of these changes relative to external ion concentrations was studied at steady-state stimulation frequencies of 1–5 Hz. Ca 2+ depletion increased from 7 to 13.1% with stimulation frequency, while K + accumulation decreased from 4.1 to 2.7%. These ionic changes (particularly Ca 2+ depletion) implicated significant decrease of intracellular Ca 2+ load at frequencies natural for rat heart.

Antisense inhibition of Na+/Ca2+ exchange during anoxia/reoxygenation in ventricular myocytes

2001 ◽  
Vol 281 (5) ◽  
pp. H2184-H2190 ◽  
Author(s):  
B. N. Eigel ◽  
R. W. Hadley
Keyword(s):  
Guinea Pig ◽  
Antisense Oligonucleotide ◽  
Ventricular Myocytes ◽  
Antisense Inhibition ◽  
Start Site ◽  
Intracellular Ca

This study investigated the role of the Na+/Ca2+ exchanger (NCX) in regulating cytosolic intracellular Ca2+concentration ([Ca2+]i) during anoxia/reoxygenation in guinea pig ventricular myocytes. The hypothesis that the NCX is the predominant mechanism mediating [Ca2+]i overload in this model was tested through inhibition of NCX expression by an antisense oligonucleotide. Immunocytochemistry revealed that this antisense oligonucleotide, directed at the area around the start site of the guinea pig NCX1, specifically reduced NCX expression in cultured adult myocytes by 90 ± 4%. Antisense treatment inhibited evoked NCX activity by 94 ± 3% and decreased the rise in [Ca2+]i during anoxia/reoxygenation by 95 ± 3%. These data suggest that NCX is the predominant mechanism mediating Ca2+ overload during anoxia/reoxygenation in guinea-pig ventricular myocytes.

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