https://ogma.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:46774 Wed 30 Nov 2022 13:14:32 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:5776 Wed 27 Jul 2022 15:01:04 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:34969 d = 121 ± 14 nM. Ex-vivo phosphorylation/dephosphorylation experiments suggested that the divergent CaM regulation of healthy and failing human RyR2 was caused by differences in RyR2 phosphorylation by protein kinase A and Ca-CaM-dependent kinase II. Ca²⁺-spark measurements in murine cardiomyocytes harbouring RyR2 phosphomimetic or phosphoablated mutants at S2814 and S2808 suggest that phosphorylation of residues corresponding to either human RyR2-S2808 or S2814 is both necessary and sufficient for RyR2 regulation by CaM. Our results challenge the current concept that CaM universally functions as a canonical inhibitor of RyR2 across species. Rather, CaM's biological action on human RyR2 appears to be more nuanced, with inhibitory activity only on phosphorylated RyR2 channels, which occurs during exercise or in patients with heart failure.]]> Wed 24 Jun 2020 11:42:42 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:26929 Wed 11 Apr 2018 15:54:38 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:1802 Wed 11 Apr 2018 13:46:30 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:39630 N-methyl flecainide) and showed that N-methylation reduces flecainide’s inhibitory potency on RyR2 channels incorporated into artificial lipid bilayers. N-methylation did not alter flecainide’s inhibitory activity on human cardiac sodium channels expressed in HEK293T cells. Antiarrhythmic efficacy was tested utilizing a Casq2 (cardiac calsequestrin) knockout (Casq2−/−) CPVT mouse model. In membrane-permeabilized Casq2−/− cardiomyocytes—lacking intact sarcolemma and devoid of sodium channel contribution—flecainide, but not its analogues, suppressed RyR2-mediated Ca release at clinically relevant concentrations. In voltage-clamped, intact Casq2−/− cardiomyocytes pretreated with tetrodotoxin to inhibit sodium channels and isolate the effect of flecainide on RyR2, flecainide significantly reduced the frequency of spontaneous sarcoplasmic reticulum Ca release, while QX-flecainide and N-methyl flecainide did not. In vivo, flecainide effectively suppressed catecholamine-induced ventricular tachyarrhythmias in Casq2−/− mice, whereas N-methyl flecainide had no significant effect on arrhythmia burden, despite comparable sodium channel block. Conclusions: Flecainide remains an effective inhibitor of RyR2-mediated arrhythmogenic Ca release even when cardiac sodium channels are blocked. In mice with CPVT, sodium channel block alone did not prevent ventricular tachycardia. Hence, RyR2 channel inhibition likely constitutes the principal mechanism of antiarrhythmic action of flecainide in CPVT.]]> Thu 16 Jun 2022 11:46:05 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:7011 Sat 24 Mar 2018 08:38:04 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:11317 Sat 24 Mar 2018 08:12:35 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:17918 Sat 24 Mar 2018 07:56:14 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:5571 Sat 24 Mar 2018 07:49:18 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:398 Sat 24 Mar 2018 07:42:31 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:27466 2+) into cardiac cells and between their intracellular organelles, and any disruption can lead to arrhythmia and sudden cardiac death. Electrical excitation of the surface membrane activates voltage-dependent L-type Ca²⁺ channels to open and allow Ca²⁺ to enter the cytoplasm. The subsequent increase in cytoplasmic Ca²⁺ concentration activates calcium release channels (RyR2) located at specialised Ca2+ release sites in the sarcoplasmic reticulum (SR), which serves as an intracellular Ca²⁺ store. Animal models have provided valuable insights into how intracellular Ca²⁺ transport mechanisms are altered in human heart failure. The aim of this review is to examine how Ca²⁺ release sites are remodelled in heart failure and how this affects intracellular Ca²⁺ transport with an emphasis on Ca²⁺ release mechanisms in the SR. Current knowledge on how heart failure alters the regulation of RyR2 by Ca²⁺ and Mg²⁺ and how these mechanisms control the activity of RyR2 in the confines of the Ca²⁺ release sites is reviewed.]]> Sat 24 Mar 2018 07:32:43 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:33275 Mon 24 Sep 2018 13:26:23 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:33274 Mon 24 Sep 2018 13:26:22 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:33272 2+ release channels in the sarcoplasmic reticulum in striated muscle which play an important role in excitation-contraction coupling and cardiac pacemaking. Single channel recordings have revealed a wealth of information about ligand regulation of RyRs from mammalian skeletal and cardiac muscle (RyR1 and RyR2, respectively). RyR subunit has a Ca²⁺ activation site located in the luminal and cytoplasmic domains of the RyR. These sites synergistically feed into a common gating mechanism for channel activation by luminal and cytoplasmic Ca²⁺. RyRs also possess two inhibitory sites in their cytoplasmic domains with Ca²⁺ affinities of the order of 1 µM and 1 mM. Magnesium competes with Ca²⁺ at these sites to inhibit RyRs and this plays an important role in modulating their Ca²⁺-dependent activity in muscle. This review focuses on how these sites lead to RyR modulation by Ca²⁺ and Mg²⁺ and how these mechanisms control Ca²⁺ release in excitation-contraction coupling and cardiac pacemaking.]]> Mon 24 Sep 2018 13:26:20 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:33273 2+ release, leading to sarcoplasmic reticulum Ca²⁺ depletion, reduced cardiac function, and providing cell protection against ischemia-reperfusion injury. Anesthetic activation of ryanodine receptor 2 is poorly defined, leaving aspects of the protective mechanism uncertain. Methods: Ryanodine receptor 2 from the sheep heart was incorporated into artificial lipid bilayers, and their gating properties were measured in response to five halogenated anesthetics. Results: Each anesthetic rapidly and reversibly activated ryanodine receptor 2, but only from the cytoplasmic side. Relative activation levels were as follows: halothane (approximately 4-fold; n = 8), desflurane and enflurane (approximately 3-fold,n = 9), and isoflurane and sevoflurane (approximately 1.5-fold, n = 7, 10). Half-activating concentrations (Kₐ) were in the range 1.3 to 2.1 mM (1.4 to 2.6 minimum alveolar concentration [MAC]) with the exception of isoflurane (5.3 mM, 6.6 minimum alveolar concentration). Dantrolene (10 µM with 100 nM calmodulin) inhibited ryanodine receptor 2 by 40% but did not alter the Kₐ for halothane activation. Halothane potentiated luminal and cytoplasmic Ca²⁺ activation of ryanodine receptor 2 but had no effect on Mg²⁺ inhibition. Halothane activated ryanodine receptor 2 in the absence and presence (2 mM) of adenosine triphosphate (ATP). Adenosine, a competitive antagonist to ATP activation of ryanodine receptor 2, did not antagonize halothane activation in the absence of ATP. Conclusions: At clinical concentrations (1 MAC), halothane desflurane and enflurane activated ryanodine receptor 2, whereas isoflurane and sevoflurane were ineffective. Dantrolene inhibition of ryanodine receptor 2 substantially negated the activating effects of anesthetics. Halothane acted independently of the adenine nucleotide-binding site on ryanodine receptor 2. The previously observed adenosine antagonism of halothane activation of sarcoplasmic reticulum Ca²⁺ release was due to competition between adenosine and ATP, rather than between halothane and ATP.]]> Mon 24 Sep 2018 13:26:20 AEST ]]>