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.

Na+/Ca2+ exchange and its role in intracellular Ca2+ regulation in guinea pig detrusor smooth muscle

2001 ◽  
Vol 280 (5) ◽  
pp. C1090-C1096 ◽  
Author(s):  
C. Wu ◽  
C. H. Fry
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Guinea Pig ◽  
Outward Current ◽  
Detrusor Smooth Muscle ◽  
Small Rise ◽  
Intracellular Ca ◽  
Net Flux ◽  
Isolated Smooth Muscle Cells

The role of Na+/Ca2+ exchange in regulating intracellular Ca2+ concentration ([Ca2+]i) in isolated smooth muscle cells from the guinea pig urinary bladder was investigated. Incremental reduction of extracellular Na+ concentration resulted in a graded rise of [Ca2+]i; 50–100 μM strophanthidin also increased [Ca2+]i. A small outward current accompanied the rise of [Ca2+]i in low-Na+ solutions (17.1 ± 1.8 pA in 29.4 mM Na+). The quantity of Ca2+ influx through the exchanger was estimated from the charge carried by the outward current and was ∼30 times that which is necessary to account for the rise of [Ca2+]i, after correction was made for intracellular Ca2+ buffering. Ca2+ influx through the exchanger was able to load intracellular Ca2+ stores. It is concluded that the level of resting [Ca2+]i is not determined by the exchanger, and under resting conditions (membrane potential −50 to −60 mV), there is little net flux through the exchanger. However, a small rise of intracellular Na+ concentration would be sufficient to generate significant net Ca2+ influx.

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.

The Role of Gi-proteins andβ-Adrenoceptors in the Age-related Decline of Contraction in Guinea-pig Ventricular Myocytes

1997 ◽  
Vol 29 (2) ◽  
pp. 439-448 ◽  
Author(s):  
Nicola Ferrara ◽  
Michael Bö ◽  
Oliver Zolk ◽  
Peter O»Gara ◽  
Sian E. Harding
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Age Related ◽  
Gi Proteins

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.

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