scholarly journals Reduced junctional Na+/Ca2+-exchanger activity contributes to sarcoplasmic reticulum Ca2+ leak in junctophilin-2-deficient mice

2014 ◽  
Vol 307 (9) ◽  
pp. H1317-H1326 ◽  
Author(s):  
Wei Wang ◽  
Andrew P. Landstrom ◽  
Qiongling Wang ◽  
Michelle L. Munro ◽  
David Beavers ◽  
...  
Keyword(s):  
Heart Failure ◽  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Rapid Development ◽  
Mouse Heart ◽  
Cellular Mechanisms ◽  
Open Probability ◽  
Deficient Mice

Expression silencing of junctophilin-2 (JPH2) in mouse heart leads to ryanodine receptor type 2 (RyR2)-mediated sarcoplasmic reticulum (SR) Ca2+ leak and rapid development of heart failure. The mechanism and physiological significance of JPH2 in regulating RyR2-mediated SR Ca2+ leak remains elusive. We sought to elucidate the role of JPH2 in regulating RyR2-mediated SR Ca2+ release in the setting of cardiac failure. Cardiac myocytes isolated from tamoxifen-inducible conditional knockdown mice of JPH2 (MCM-shJPH2) were subjected to confocal Ca2+ imaging. MCM-shJPH2 cardiomyocytes exhibited an increased spark frequency width with altered spark morphology, which caused increased SR Ca2+ leakage. Single channel studies identified an increased RyR2 open probability in MCM-shJPH2 mice. The increase in spark frequency and width was observed only in MCM-shJPH2 and not found in mice with increased RyR2 open probability with native JPH2 expression. Na+/Ca2+-exchanger (NCX) activity was reduced by 50% in MCM-shJPH2 with no detectable change in NCX expression. Additionally, 50% inhibition of NCX through Cd2+ administration alone was sufficient to increase spark width in myocytes obtained from wild-type mice. Additionally, superresolution analysis of RyR2 and NCX colocalization showed a reduced overlap between RyR2 and NCX in MCM-shJPH2 mice. In conclusion, decreased JPH2 expression causes increased SR Ca2+ leakage by directly increasing open probability of RyR2 and by indirectly reducing junctional NCX activity through increased dyadic cleft Ca2+. This demonstrates two novel and independent cellular mechanisms by which JPH2 regulates RyR2-mediated SR Ca2+ leak and heart failure development.

scholarly journals Intracellular Na+ Modulates Pacemaking Activity in Murine Sinoatrial Node Myocytes: An In Silico Analysis

2021 ◽  
Vol 22 (11) ◽  
pp. 5645
Author(s):  
Stefano Morotti ◽  
Haibo Ni ◽  
Colin H. Peters ◽  
Christian Rickert ◽  
Ameneh Asgari-Targhi ◽  
...  
Keyword(s):  
Heart Failure ◽  
Membrane Potential ◽  
In Silico ◽  
Sinoatrial Node ◽  
In Silico Analysis ◽  
Ankyrin B ◽  
Deficient Mice ◽  
Silico Analysis ◽  
Bursting Activity

Background: The mechanisms underlying dysfunction in the sinoatrial node (SAN), the heart’s primary pacemaker, are incompletely understood. Electrical and Ca2+-handling remodeling have been implicated in SAN dysfunction associated with heart failure, aging, and diabetes. Cardiomyocyte [Na+]i is also elevated in these diseases, where it contributes to arrhythmogenesis. Here, we sought to investigate the largely unexplored role of Na+ homeostasis in SAN pacemaking and test whether [Na+]i dysregulation may contribute to SAN dysfunction. Methods: We developed a dataset-specific computational model of the murine SAN myocyte and simulated alterations in the major processes of Na+ entry (Na+/Ca2+ exchanger, NCX) and removal (Na+/K+ ATPase, NKA). Results: We found that changes in intracellular Na+ homeostatic processes dynamically regulate SAN electrophysiology. Mild reductions in NKA and NCX function increase myocyte firing rate, whereas a stronger reduction causes bursting activity and loss of automaticity. These pathologic phenotypes mimic those observed experimentally in NCX- and ankyrin-B-deficient mice due to altered feedback between the Ca2+ and membrane potential clocks underlying SAN firing. Conclusions: Our study generates new testable predictions and insight linking Na+ homeostasis to Ca2+ handling and membrane potential dynamics in SAN myocytes that may advance our understanding of SAN (dys)function.

scholarly journals Interactions of a Reversible Ryanoid (21-Amino-9α-Hydroxy-Ryanodine) with Single Sheep Cardiac Ryanodine Receptor Channels

1998 ◽  
Vol 112 (1) ◽  
pp. 55-69 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L. Sutko ◽  
Alan J. Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Site ◽  
Single Channel ◽  
Single Channels ◽  
Open Probability ◽  
Release Channel ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Protein ◽  
High Affinity ◽  
Conductance State

The binding of ryanodine to a high affinity site on the sarcoplasmic reticulum Ca2+-release channel results in a dramatic alteration in both gating and ion handling; the channel enters a high open probability, reduced-conductance state. Once bound, ryanodine does not dissociate from its site within the time frame of a single channel experiment. In this report, we describe the interactions of a synthetic ryanoid, 21-amino-9α-hydroxy-ryanodine, with the high affinity ryanodine binding site on the sheep cardiac sarcoplasmic reticulum Ca2+-release channel. The interaction of 21-amino-9α-hydroxy-ryanodine with the channel induces the occurrence of a characteristic high open probability, reduced-conductance state; however, in contrast to ryanodine, the interaction of this ryanoid with the channel is reversible under steady state conditions, with dwell times in the modified state lasting seconds. By monitoring the reversible interaction of this ryanoid with single channels under voltage clamp conditions, we have established a number of novel features of the ryanoid binding reaction. (a) Modification of channel function occurs when a single molecule of ryanoid binds to the channel protein. (b) The ryanoid has access to its binding site only from the cytosolic side of the channel and the site is available only when the channel is open. (c) The interaction of 21-amino-9α-hydroxy-ryanodine with its binding site is influenced strongly by transmembrane voltage. We suggest that this voltage dependence is derived from a voltage-driven conformational alteration of the channel protein that changes the affinity of the binding site, rather than the translocation of the ryanoid into the voltage drop across the channel.

scholarly journals Towards a Consensus on Alzheimer’s Disease Comorbidity?

2021 ◽  
Vol 10 (19) ◽  
pp. 4360
Author(s):  
Iska Avitan ◽  
Yudit Halperin ◽  
Trishna Saha ◽  
Naamah Bloch ◽  
Dana Atrahimovich ◽  
...  
Keyword(s):  
Risk Factors ◽  
Heart Failure ◽  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Potential Role ◽  
Oxygen Species ◽  
Degenerative Diseases ◽  
Comorbid Diseases

Alzheimer’s disease (AD) is often comorbid with other pathologies. First, we review shortly the diseases most associated with AD in the clinic. Then we query PubMed citations for the co-occurrence of AD with other diseases, using a list of 400 common pathologies. Significantly, AD is found to be associated with schizophrenia and psychosis, sleep insomnia and apnea, type 2 diabetes, atherosclerosis, hypertension, cardiovascular diseases, obesity, fibrillation, osteoporosis, arthritis, glaucoma, metabolic syndrome, pain, herpes, HIV, alcoholism, heart failure, migraine, pneumonia, dyslipidemia, COPD and asthma, hearing loss, and tobacco smoking. Trivially, AD is also found to be associated with several neurodegenerative diseases, which are disregarded. Notably, our predicted results are consistent with the previously published clinical data and correlate nicely with individual publications. Our results emphasize risk factors and promulgate diseases often associated with AD. Interestingly, the comorbid diseases are often degenerative diseases exacerbated by reactive oxygen species, thus underlining the potential role of antioxidants in the treatment of AD and comorbid diseases.

Abstract 950: Direct Evidence for an Important Role of Agonist-independent Constitutive I K,ACh Channel Activity in Atrial Tachycardia Remodeling

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Niels Voigt ◽  
Ange Maguy ◽  
Yung-Hsin Yeh ◽  
Xiao-Yan Qi ◽  
Ursula Ravens ◽  
...  
Keyword(s):  
Atrial Tachycardia ◽  
Single Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Direct Demonstration ◽  
Open Time ◽  
Therapy Target ◽  
Channel Properties ◽  
Constitutively Active

Background: Although atrial tachycardia (AT) appears to promote agonist-independent constitutively active I K,ACh that increases susceptibility to AF, direct demonstration of dysregulated I K,ACh channel function is lacking. We studied AT effects on single I K,ACh channel activity in dog atria. Methods: I K,ACh channel activity was recorded with cell-attached patch clamp in isolated atrial myocytes of control (CTL) and AT (7 days, 400 min −1 ) dogs. Results : AT prolonged inducible AF duration from 44±22 to 413±167 s; N=9 dogs/gp, P<0.001. In the absence of cholinergic stimulation, single-channel openings with typical I K,ACh conductance and rectification were observed in CTL and AT (Figure ). AT produced prominent agonist-independent I K,ACh activity due to 7-fold increased opening frequency (f o ) and 10-fold increased open probability (P o ) vs CTL (P<0.01 for each), but unaltered open time and single channel conductance. With maximum I K,ACh activation (10 μm carbachol, CCh), f o was 38% lower, open time constant 25% higher, and P o and unitary conductance unchanged for AT vs CTL. The selective Kir3 blocker tertiapin (100 nM) reduced f o and P o by 48% and 51% (P<0.05 each) without altering other channel properties, confirming the identity of I K,ACh. Conclusions : AT produces prominent agonist-independent constitutive single-channel I K,ACh activity, providing a molecular basis for previously-observed AT-enhanced macroscopic I K,ACh , as well as associated AP-shortening and tertiapin-suppressible AF promotion. These results suggest an important role for constitutively active I K,ACh channels in AT-remodeling and support their interest as a potential novel AF-therapy target.

Eicosanoids modulate apical Ca(2+)-dependent K+ channels in cultured rabbit principal cells

1992 ◽  
Vol 263 (1) ◽  
pp. F116-F126 ◽  
Author(s):  
B. N. Ling ◽  
C. L. Webster ◽  
D. C. Eaton
Keyword(s):  
Single Channel ◽  
Primary Cultures ◽  
Cell Volume Regulation ◽  
Principal Cell ◽  
Resting Membrane Potential ◽  
Open Probability ◽  
Channel Activation ◽  
K Channels ◽  
Pg E2

Patch clamp technology was utilized to study the effects of apical phospholipase A2 (PLA2) metabolites on “maxi K” channels in the principal cell apical membrane of rabbit cortical collecting tubule (CCT) primary cultures (B. N. Ling, C. F. Hinton, and D. C. Eaton. Kidney Int. 40: 441–452, 1991). At resting membrane potential, this channel is quiescent in the cell-attached configuration. Apical application of the PLA2 agonist melittin (1 microgram/ml) for 10 min increased single-channel open probability (Po) from 0.0004 +/- 0.0010 to 0.11 +/- 0.05. Similarly, apical exposure to 50 microM arachidonic acid (AA) or 0.5 microM prostaglandin (PG) E2, but not 0.5 microM PGF2 alpha, also increased channel activity. Conversely, 10 microM of the PLA2 antagonist quinacrine applied apically decreased Po. Removal of apical bath Ca2+ did not prevent melittin-, AA-, or PGE2-induced channel activation. We then examined the role of maxi K channels and eicosanoids in principal cell volume regulation. Within seconds of reducing basolateral bath tonicity (285 to 214 mosmol/kgH2O), NPo (i.e., no. of channels x Po) initially increased approximately 200%, followed by a delayed but prolonged activation phase that was attenuated by removal of apical bath Ca2+. Pretreatment with 10 microM quinacrine, 100 microM indomethacin (cyclooxygenase inhibitor), or 0.25 microM thapsigargin (to deplete intracellular Ca2+ stores) abolished the initial phase of swelling-induced channel activation.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Nicotinic acid–adenine dinucleotide phosphate activates the skeletal muscle ryanodine receptor

2002 ◽  
Vol 367 (2) ◽  
pp. 423-431 ◽  
Author(s):  
Martin HOHENEGGER ◽  
Josef SUKO ◽  
Regina GSCHEIDLINGER ◽  
Helmut DROBNY ◽  
Andreas ZIDAR
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Nicotinic Acid ◽  
Ryanodine Receptor ◽  
Spatial Information ◽  
Single Channel ◽  
Reversal Potential ◽  
Open Probability ◽  
Release Channel

Calcium is a universal second messenger. The temporal and spatial information that is encoded in Ca2+-transients drives processes as diverse as neurotransmitter secretion, axonal outgrowth, immune responses and muscle contraction. Ca2+-release from intracellular Ca2+ stores can be triggered by diffusible second messengers like InsP3, cyclic ADP-ribose or nicotinic acid—adenine dinucleotide phosphate (NAADP). A target has not yet been identified for the latter messenger. In the present study we show that nanomolar concentrations of NAADP trigger Ca2+-release from skeletal muscle sarcoplasmic reticulum. This was due to a direct action on the Ca2+-release channel/ryanodine receptor type-1, since in single channel recordings, NAADP increased the open probability of the purified channel protein. The effects of NAADP on Ca2+-release and open probability of the ryanodine receptor occurred over a similar concentration range (EC5030nM) and were specific because (i) they were blocked by Ruthenium Red and ryanodine, (ii) the precursor of NAADP, NADP, was ineffective at equimolar concentrations, (iii) NAADP did not affect the conductance and reversal potential of the ryanodine receptor. Finally, we also detected an ADP-ribosyl cyclase activity in the sarcoplasmic reticulum fraction of skeletal muscle. This enzyme was not only capable of synthesizing cyclic GDP-ribose but also NAADP, with an activity of 0.25nmol/mg/min. Thus, we conclude that NAADP is generated in the vicinity of type 1 ryanodine receptor and leads to activation of this ion channel.

scholarly journals Divalent cation activation and inhibition of single calcium release channels from sheep cardiac sarcoplasmic reticulum.

1990 ◽  
Vol 95 (5) ◽  
pp. 981-1005 ◽  
Author(s):  
R H Ashley ◽  
A J Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Calcium Release ◽  
Single Channel ◽  
Fluctuation Analysis ◽  
Open Probability ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Opening ◽  
Lifetime Analysis ◽  
Single Channel Currents

Single Ca2+ release channels from vesicles of sheep cardiac junctional sarcoplasmic reticulum have been incorporated into uncharged planar lipid bilayers. Single-channel currents were recorded from Ca2(+)-activated channels that had a Ca2+ conductance of approximately 90 pS. Channel open probability increased sublinearly as the concentration of free Ca2+ was raised at the myoplasmic face, and without additional agonists the channels could not be fully activated even by 100 microM free Ca2+. Lifetime analysis revealed a minimum of two open and three closed states, and indicates that Ca2+ activated the channels by interacting with at least one of the closed states to increase the rate of channel opening. Correlations between adjacent lifetimes suggested there were at least two pathways between the open- and closed-state aggregates. An analysis of bursting behavior also revealed correlations between successive burst lengths and the number of openings per burst. The latter had two geometric components, providing additional evidence for at least two open states. One component appeared to comprise unit bursts, and the lifetime of most of these fell within the dominant shorter open-time distribution associated with over 90% of all openings. A cyclic gating scheme is proposed, with channel activation regulated by the binding of Ca2+ to a closed conformation of the channel protein. Mg2+ may inhibit activation by competing for this binding site, but lifetime and fluctuation analysis suggested that once activated the channels continue to gate normally.

Modulation of human cardiovascular outward rectifying chloride channel by intra- and extracellular ATP

2007 ◽  
Vol 293 (6) ◽  
pp. H3471-H3479 ◽  
Author(s):  
Gong Xin Liu ◽  
Sanjay Vepa ◽  
Michael Artman ◽  
William A. Coetzee
Keyword(s):  
Coronary Artery ◽  
Single Channel ◽  
Atp Release ◽  
Extracellular Atp ◽  
Human Coronary Artery ◽  
Open Probability ◽  
Pipette Solution ◽  
Cellular Excitability ◽  
Human Cardiovascular System

The macroscopic volume-regulated anion current (VRAC) is regulated by both intracellular and extracellular ATP, which has important implications in signaling and regulation of cellular excitability. The outwardly rectifying Cl− channel (ORCC) is a major contributor to the VRAC. This study investigated the effects of intracellular and extracellular ATP on the ORCCs expressed in the human cardiovascular system. With inside-out single-channel patch-clamp techniques, ORCCs were recorded from myocytes isolated from human atrium and septal ventricle and from primary cells originating from human coronary artery endothelium and human coronary artery smooth muscle. ORCCs from all of these tissues had similar biophysical properties, i.e., they were outwardly rectifying in symmetrical Cl− solutions, exhibited a slope conductance of ∼90–100 pS at positive potentials and ∼22 pS at negative potentials, and had a high open probability that was independent of voltage or time. The presence of ATP at the cytosolic face of the membrane increased the number of patches that contained functional ORCC but had no effect on gating. In contrast, “extracellular” ATP (in pipette solution) had no effect on the proportion of patches in which ORCC was detected but strongly reduced the open probability by increasing the closed dwell time. The potency order for nucleotides to affect gating was ATPγS > ATP = UTP > ADP > AMP, which suggests that a negatively charged phosphate group is involved in ORCC block. Our findings are consistent with a role of ORCC in the human cardiovasculature (atrium, ventricle, and coronary arteries). Regulation of ORCC by extracellular ATP suggests that this channel may have an important role in maintaining electrical activity and membrane potential under conditions in which extracellular ATP levels are elevated, such as with ATP release from nerve endings or during pathophysiological conditions.

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