26
|
Hewawasam RP, Liu D, Casarotto MG, Board PG, Dulhunty AF. The GSTM2 C-Terminal Domain Depresses Contractility and Ca2+ Transients in Neonatal Rat Ventricular Cardiomyocytes. PLoS One 2016; 11:e0162415. [PMID: 27612301 PMCID: PMC5017731 DOI: 10.1371/journal.pone.0162415] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 08/22/2016] [Indexed: 11/25/2022] Open
Abstract
The cardiac ryanodine receptor (RyR2) is an intracellular ion channel that regulates Ca2+ release from the sarcoplasmic reticulum (SR) during excitation–contraction coupling in the heart. The glutathione transferases (GSTs) are a family of phase II detoxification enzymes with additional functions including the selective inhibition of RyR2, with therapeutic implications. The C-terminal half of GSTM2 (GSTM2C) is essential for RyR2 inhibition, and mutations F157A and Y160A within GSTM2C prevent the inhibitory action. Our objective in this investigation was to determine whether GSTM2C can enter cultured rat neonatal ventricular cardiomyocytes and influence contractility. We show that oregon green-tagged GSTM2C (at 1 μM) is internalized into the myocytes and it reduces spontaneous contraction frequency and myocyte shortening. Field stimulation of myocytes evoked contraction in the same percentage of myocytes treated either with media alone or media plus 15 μM GSTM2C. Myocyte shortening during contraction was significantly reduced by exposure to 15 μM GSTM2C, but not 5 and 10 μM GSTM2C and was unaffected by exposure to 15 μM of the mutants Y160A or F157A. The amplitude of the Ca2+ transient in the 15 μM GSTM2C - treated myocytes was significantly decreased, the rise time was significantly longer and the decay time was significantly shorter than in control myocytes. The Ca2+ transient was not altered by exposure to Y160A or F157A. The results are consistent with GSTM2C entering the myocytes and inhibiting RyR2, in a manner that indicates a possible therapeutic potential for treatment of arrhythmia in the neonatal heart.
Collapse
|
27
|
Willemse H, Theodoratos A, Smith PN, Dulhunty AF. Unexpected dependence of RyR1 splice variant expression in human lower limb muscles on fiber-type composition. Pflugers Arch 2015; 468:269-78. [PMID: 26438192 DOI: 10.1007/s00424-015-1738-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 09/14/2015] [Accepted: 09/29/2015] [Indexed: 10/23/2022]
Abstract
The skeletal muscle ryanodine receptor Ca(2+) release channel (RyR1), essential for excitation-contraction (EC) coupling, demonstrates a known developmentally regulated alternative splicing in the ASI region. We now find unexpectedly that the expression of the splice variants is closely related to fiber type in adult human lower limb muscles. We examined the distribution of myosin heavy chain isoforms and ASI splice variants in gluteus minimus, gluteus medius and vastus medialis from patients aged 45 to 85 years. There was a strong positive correlation between ASI(+)RyR1 and the percentage of type 2 fibers in the muscles (r = 0.725), and a correspondingly strong negative correlation between the percentages of ASI(+)RyR1 and percentage of type 1 fibers. When the type 2 fiber data were separated into type 2X and type 2A, the correlation with ASI(+)RyR1 was stronger in type 2X fibers (r = 0.781) than in type 2A fibers (r = 0.461). There was no significant correlation between age and either fiber-type composition or ASI(+)RyR1/ASI(-)RyR1 ratio. The results suggest that the reduced expression of ASI(-)RyR1 during development may reflect a reduction in type 1 fibers during development. Preferential expression of ASI(-) RyR1, having a higher gain of in Ca(2+) release during EC coupling than ASI(+)RyR1, may compensate for the reduced terminal cisternae volume, fewer junctional contacts and reduced charge movement in type 1 fibers.
Collapse
|
28
|
Samarasinghe K, Liu D, Tummala P, Cappello J, Pace SM, Arnolda L, Casarotto MG, Dulhunty AF, Board PG. Glutathione transferase M2 variants inhibit ryanodine receptor function in adult mouse cardiomyocytes. Biochem Pharmacol 2015; 97:269-80. [DOI: 10.1016/j.bcp.2015.08.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Accepted: 08/03/2015] [Indexed: 11/16/2022]
|
29
|
Rebbeck RT, Willemse H, Groom L, Casarotto MG, Board PG, Beard NA, Dirksen RT, Dulhunty AF. Regions of ryanodine receptors that influence activation by the dihydropyridine receptor β1a subunit. Skelet Muscle 2015. [PMID: 26203350 PMCID: PMC4510890 DOI: 10.1186/s13395-015-0049-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Background Although excitation-contraction (EC) coupling in skeletal muscle relies on physical activation of the skeletal ryanodine receptor (RyR1) Ca2+ release channel by dihydropyridine receptors (DHPRs), the activation pathway between the DHPR and RyR1 remains unknown. However, the pathway includes the DHPR β1a subunit which is integral to EC coupling and activates RyR1. In this manuscript, we explore the isoform specificity of β1a activation of RyRs and the β1a binding site on RyR1. Methods We used lipid bilayers to measure single channel currents and whole cell patch clamp to measure L-type Ca2+ currents and Ca2+ transients in myotubes. Results We demonstrate that both skeletal RyR1 and cardiac RyR2 channels in phospholipid bilayers are activated by 10–100 nM of the β1a subunit. Activation of RyR2 by 10 nM β1a was less than that of RyR1, suggesting a reduced affinity of RyR2 for β1a. A reduction in activation was also observed when 10 nM β1a was added to the alternatively spliced (ASI(−)) isoform of RyR1, which lacks ASI residues (A3481-Q3485). It is notable that the equivalent region of RyR2 also lacks four of five ASI residues, suggesting that the absence of these residues may contribute to the reduced 10 nM β1a activation observed for both RyR2 and ASI(−)RyR1 compared to ASI(+)RyR1. We also investigated the influence of a polybasic motif (PBM) of RyR1 (K3495KKRRDGR3502) that is located immediately downstream from the ASI residues and has been implicated in EC coupling. We confirmed that neutralizing the basic residues in the PBM (RyR1 K-Q) results in an ~50 % reduction in Ca2+ transient amplitude following expression in RyR1-null (dyspedic) myotubes and that the PBM is also required for β1a subunit activation of RyR1 channels in lipid bilayers. These results suggest that the removal of β1a subunit interaction with the PBM in RyR1 could contribute directly to ~50 % of the Ca2+ release generated during skeletal EC coupling. Conclusions We conclude that the β1a subunit likely binds to a region that is largely conserved in RyR1 and RyR2 and that this region is influenced by the presence of the ASI residues and the PBM in RyR1. Electronic supplementary material The online version of this article (doi:10.1186/s13395-015-0049-3) contains supplementary material, which is available to authorized users.
Collapse
|
30
|
Walweel K, Li J, Molenaar P, Imtiaz MS, Quail A, dos Remedios CG, Beard NA, Dulhunty AF, van Helden DF, Laver DR. Differences in the regulation of RyR2 from human, sheep, and rat by Ca²⁺ and Mg²⁺ in the cytoplasm and in the lumen of the sarcoplasmic reticulum. ACTA ACUST UNITED AC 2015; 144:263-71. [PMID: 25156119 PMCID: PMC4144672 DOI: 10.1085/jgp.201311157] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cardiac ryanodine receptors (RyR2) from humans, rats, and sheep show differential sensitivity to calcium and magnesium, with regulation of human RyR2 resembling that of sheep more than that of rat. Regulation of the cardiac ryanodine receptor (RyR2) by intracellular Ca2+ and Mg2+ plays a key role in determining cardiac contraction and rhythmicity, but their role in regulating the human RyR2 remains poorly defined. The Ca2+- and Mg2+-dependent regulation of human RyR2 was recorded in artificial lipid bilayers in the presence of 2 mM ATP and compared with that in two commonly used animal models for RyR2 function (rat and sheep). Human RyR2 displayed cytoplasmic Ca2+ activation (Ka = 4 µM) and inhibition by cytoplasmic Mg2+ (Ki = 10 µM at 100 nM Ca2+) that was similar to RyR2 from rat and sheep obtained under the same experimental conditions. However, in the presence of 0.1 mM Ca2+, RyR2s from human were 3.5-fold less sensitive to cytoplasmic Mg2+ inhibition than those from sheep and rat. The Ka values for luminal Ca2+ activation were similar in the three species (35 µM for human, 12 µM for sheep, and 10 µM for rat). From the relationship between open probability and luminal [Ca2+], the peak open probability for the human RyR2 was approximately the same as that for sheep, and both were ∼10-fold greater than that for rat RyR2. Human RyR2 also showed the same sensitivity to luminal Mg2+ as that from sheep, whereas rat RyR2 was 10-fold more sensitive. In all species, modulation of RyR2 gating by luminal Ca2+ and Mg2+ only occurred when cytoplasmic [Ca2+] was <3 µM. The activation response of RyR2 to luminal and cytoplasmic Ca2+ was strongly dependent on the Mg2+ concentration. Addition of physiological levels (1 mM) of Mg2+ raised the Ka for cytoplasmic Ca2+ to 30 µM (human and sheep) or 90 µM (rat) and raised the Ka for luminal Ca2+ to ∼1 mM in all species. This is the first report of the regulation by Ca2+ and Mg2+ of native RyR2 receptor activity from healthy human hearts.
Collapse
|
31
|
Beard NA, Dulhunty AF. C-terminal residues of skeletal muscle calsequestrin are essential for calcium binding and for skeletal ryanodine receptor inhibition. Skelet Muscle 2015; 5:6. [PMID: 25861445 PMCID: PMC4389316 DOI: 10.1186/s13395-015-0029-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 01/14/2015] [Indexed: 02/05/2023] Open
Abstract
Background Skeletal muscle function depends on calcium signaling proteins in the sarcoplasmic reticulum (SR), including the calcium-binding protein calsequestrin (CSQ), the ryanodine receptor (RyR) calcium release channel, and skeletal triadin 95 kDa (trisk95) and junctin, proteins that bind to calsequestrin type 1 (CSQ1) and ryanodine receptor type 1 (RyR1). CSQ1 inhibits RyR1 and communicates store calcium load to RyR1 channels via trisk95 and/or junctin. Methods In this manuscript, we test predictions that CSQ1’s acidic C-terminus contains binding sites for trisk95 and junctin, the major calcium binding domain, and that it determines CSQ1’s ability to regulate RyR1 activity. Results Progressive alanine substitution of C-terminal acidic residues of CSQ1 caused a parallel reduction in the calcium binding capacity but did not significantly alter CSQ1’s association with trisk95/junctin or influence its inhibition of RyR1 activity. Deletion of the final seven residues in the C-terminus significantly hampered calcium binding, significantly reduced CSQ’s association with trisk95/junctin and decreased its inhibition of RyR1. Deletion of the full C-terminus further reduced calcium binding to CSQ1 altered its association with trisk95 and junctin and abolished its inhibition of RyR1. Conclusions The correlation between the number of residues mutated/deleted and binding of calcium, trisk95, and junctin suggests that binding of each depends on diffuse ionic interactions with several C-terminal residues and that these interactions may be required for CSQ1 to maintain normal muscle function.
Collapse
|
32
|
Li L, Mirza S, Richardson SJ, Gallant EM, Thekkedam C, Pace SM, Zorzato F, Liu D, Beard NA, Dulhunty AF. A new cytoplasmic interaction between junctin and ryanodine receptor Ca2+ release channels. J Cell Sci 2015; 128:951-63. [PMID: 25609705 PMCID: PMC4342579 DOI: 10.1242/jcs.160689] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Junctin, a non-catalytic splice variant encoded by the aspartate-β-hydroxylase (Asph) gene, is inserted into the membrane of the sarcoplasmic reticulum (SR) Ca2+ store where it modifies Ca2+ signalling in the heart and skeletal muscle through its regulation of ryanodine receptor (RyR) Ca2+ release channels. Junctin is required for normal muscle function as its knockout leads to abnormal Ca2+ signalling, muscle dysfunction and cardiac arrhythmia. However, the nature of the molecular interaction between junctin and RyRs is largely unknown and was assumed to occur only in the SR lumen. We find that there is substantial binding of RyRs to full junctin, and the junctin luminal and, unexpectedly, cytoplasmic domains. Binding of these different junctin domains had distinct effects on RyR1 and RyR2 activity: full junctin in the luminal solution increased RyR channel activity by ∼threefold, the C-terminal luminal interaction inhibited RyR channel activity by ∼50%, and the N-terminal cytoplasmic binding produced an ∼fivefold increase in RyR activity. The cytoplasmic interaction between junctin and RyR is required for luminal binding to replicate the influence of full junctin on RyR1 and RyR2 activity. The C-terminal domain of junctin binds to residues including the S1–S2 linker of RyR1 and N-terminal domain of junctin binds between RyR1 residues 1078 and 2156.
Collapse
|
33
|
Hanna AD, Lam A, Tham S, Dulhunty AF, Beard NA. Adverse effects of doxorubicin and its metabolic product on cardiac RyR2 and SERCA2A. Mol Pharmacol 2014; 86:438-49. [PMID: 25106424 PMCID: PMC4164980 DOI: 10.1124/mol.114.093849] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 08/08/2014] [Indexed: 11/22/2022] Open
Abstract
The use of anthracycline chemotherapeutic drugs is restricted owing to potentially fatal cardiotoxic side effects. It has been hypothesized that anthracycline metabolites have a primary role in this cardiac dysfunction; however, information on the molecular interactions of these compounds in the heart is scarce. Here we provide novel evidence that doxorubicin and its metabolite, doxorubicinol, bind to the cardiac ryanodine receptor (RyR2) and to the sarco/endoplasmic reticulum Ca(2+) ATPase (SERCA2A) and deleteriously alter their activity. Both drugs (0.01 μM-2.5 μM) activated single RyR2 channels, and this was reversed by drug washout. Both drugs caused a secondary inhibition of RyR2 activity that was not reversed by drug washout. Preincubation with the reducing agent dithiothreitol (DTT, 1 mM) prevented drug-induced inhibition of channel activity. Doxorubicin and doxorubicinol reduced the abundance of thiol groups on RyR2, further indicating that oxidation reactions may be involved in the actions of the compounds. Ca(2+) uptake into sarcoplasmic reticulum vesicles by SERCA2A was inhibited by doxorubicinol, but not doxorubicin. Unexpectedly, in the presence of DTT, doxorubicinol enhanced the rate of Ca(2+) uptake by SERCA2A. Together the evidence provided here shows that doxorubicin and doxorubicinol interact with RyR2 and SERCA2A in similar ways, but that the metabolite acts with greater efficacy than the parent compound. Both compounds modify RyR2 and SERCA2A activity by binding to the proteins and also act via thiol oxidation to disrupt SR Ca(2+) handling. These actions would have severe consequences on cardiomyocyte function and contribute to clinical symptoms of acute anthracycline cardiotoxicity.
Collapse
|
34
|
Hernández-Ochoa EO, Olojo RO, Rebbeck RT, Dulhunty AF, Schneider MF. β1a490-508, a 19-residue peptide from C-terminal tail of Cav1.1 β1a subunit, potentiates voltage-dependent calcium release in adult skeletal muscle fibers. Biophys J 2014; 106:535-47. [PMID: 24507594 DOI: 10.1016/j.bpj.2013.11.4503] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Revised: 11/11/2013] [Accepted: 11/13/2013] [Indexed: 10/25/2022] Open
Abstract
The α1 and β1a subunits of the skeletal muscle calcium channel, Cav1.1, as well as the Ca(2+) release channel, ryanodine receptor (RyR1), are essential for excitation-contraction coupling. RyR1 channel activity is modulated by the β1a subunit and this effect can be mimicked by a peptide (β1a490-524) corresponding to the 35-residue C-terminal tail of the β1a subunit. Protein-protein interaction assays confirmed a high-affinity interaction between the C-terminal tail of the β1a and RyR1. Based on previous results using overlapping peptides tested on isolated RyR1, we hypothesized that a 19-amino-acid residue peptide (β1a490-508) is sufficient to reproduce activating effects of β1a490-524. Here we examined the effects of β1a490-508 on Ca(2+) release and Ca(2+) currents in adult skeletal muscle fibers subjected to voltage-clamp and on RyR1 channel activity after incorporating sarcoplasmic reticulum vesicles into lipid bilayers. β1a490-508 (25 nM) increased the peak Ca(2+) release flux by 49% in muscle fibers. Considerably fewer activating effects were observed using 6.25, 100, and 400 nM of β1a490-508 in fibers. β1a490-508 also increased RyR1 channel activity in bilayers and Cav1.1 currents in fibers. A scrambled form of β1a490-508 peptide was used as negative control and produced negligible effects on Ca(2+) release flux and RyR1 activity. Our results show that the β1a490-508 peptide contains molecular components sufficient to modulate excitation-contraction coupling in adult muscle fibers.
Collapse
|
35
|
Hanna AD, Lam A, Thekkedam C, Gallant EM, Beard NA, Dulhunty AF. Cardiac ryanodine receptor activation by a high Ca²⁺ store load is reversed in a reducing cytoplasmic redox environment. J Cell Sci 2014; 127:4531-41. [PMID: 25146393 PMCID: PMC4197090 DOI: 10.1242/jcs.156760] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Here, we report the impact of redox potential on isolated cardiac ryanodine receptor (RyR2) channel activity and its response to physiological changes in luminal [Ca2+]. Basal leak from the sarcoplasmic reticulum is required for normal Ca2+ handling, but excess diastolic Ca2+ leak attributed to oxidative stress is thought to lower the threshold of RyR2 for spontaneous sarcoplasmic reticulum Ca2+ release, thus inducing arrhythmia in pathological situations. Therefore, we examined the RyR2 response to luminal [Ca2+] under reducing or oxidising cytoplasmic redox conditions. Unexpectedly, as luminal [Ca2+] increased from 0.1 to 1.5 mM, RyR2 activity declined when pretreated with cytoplasmic 1 mM DTT or buffered with GSH∶GSSG to a normal reduced cytoplasmic redox potential (−220 mV). Conversely, with 20 µM cytoplasmic 4,4′-DTDP or buffering of the redox potential to an oxidising value (−180 mV), RyR2 activity increased with increasing luminal [Ca2+]. The luminal redox potential was constant at −180 mV in each case. These responses to luminal [Ca2+] were maintained with cytoplasmic 2 mM Na2ATP or 5 mM MgATP (1 mM free Mg2+). Overall, the results suggest that the redox potential in the RyR2 junctional microdomain is normally more oxidised than that of the bulk cytoplasm.
Collapse
|
36
|
Rebbeck RT, Karunasekara Y, Board PG, Beard NA, Casarotto MG, Dulhunty AF. Skeletal muscle excitation–contraction coupling: Who are the dancing partners? Int J Biochem Cell Biol 2014; 48:28-38. [DOI: 10.1016/j.biocel.2013.12.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2013] [Revised: 11/29/2013] [Accepted: 12/04/2013] [Indexed: 01/15/2023]
|
37
|
Steele GA, Beard NA, Board PG, Dulhunty AF. CLIC-2 Determines FKBP12 and FKBP12.6 Association with Ryanodine Receptor Calcium Release Channels. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.738] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
|
38
|
Casarotto MG, Karunasekara Y, Aditya S, Cappello J, Dulhunty AF, Board PG, Oakley AJ, Norris NC. Structural and Binding Studies of the Cav1.1 β1A Subunit. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2531] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
|
39
|
Hanna AD, Lam A, Dulhunty AF, Beard NA. Mechanisms of Anthracycline-Induced Dysfunction of Calcium Handling Proteins in the Heart. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
|
40
|
Li J, Imtiaz MS, Beard NA, Dulhunty AF, Thorne R, vanHelden DF, Laver DR. ß-Adrenergic stimulation increases RyR2 activity via intracellular Ca2+ and Mg2+ regulation. PLoS One 2013; 8:e58334. [PMID: 23533585 PMCID: PMC3606165 DOI: 10.1371/journal.pone.0058334] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 02/02/2013] [Indexed: 01/19/2023] Open
Abstract
Here we investigate how ß-adrenergic stimulation of the heart alters regulation of ryanodine receptors (RyRs) by intracellular Ca2+ and Mg2+ and the role of these changes in SR Ca2+ release. RyRs were isolated from rat hearts, perfused in a Langendorff apparatus for 5 min and subject to 1 min perfusion with 1 µM isoproterenol or without (control) and snap frozen in liquid N2 to capture their phosphorylation state. Western Blots show that RyR2 phosphorylation was increased by isoproterenol, confirming that RyR2 were subject to normal ß-adrenergic signaling. Under basal conditions, S2808 and S2814 had phosphorylation levels of 69% and 15%, respectively. These levels were increased to 83% and 60%, respectively, after 60 s of ß-adrenergic stimulation consistent with other reports that ß-adrenergic stimulation of the heart can phosphorylate RyRs at specific residues including S2808 and S2814 causing an increase in RyR activity. At cytoplasmic [Ca2+] <1 µM, ß-adrenergic stimulation increased luminal Ca2+ activation of single RyR channels, decreased luminal Mg2+ inhibition and decreased inhibition of RyRs by mM cytoplasmic Mg2+. At cytoplasmic [Ca2+] >1 µM, ß-adrenergic stimulation only decreased cytoplasmic Mg2+ and Ca2+ inhibition of RyRs. The Ka and maximum levels of cytoplasmic Ca2+ activation site were not affected by ß-adrenergic stimulation. Our RyR2 gating model was fitted to the single channel data. It predicted that in diastole, ß-adrenergic stimulation is mediated by 1) increasing the activating potency of Ca2+ binding to the luminal Ca2+ site and decreasing its affinity for luminal Mg2+ and 2) decreasing affinity of the low-affinity Ca2+/Mg2+ cytoplasmic inhibition site. However in systole, ß-adrenergic stimulation is mediated mainly by the latter.
Collapse
|
41
|
Dulhunty AF, Wium E, Li L, Hanna AD, Mirza S, Talukder S, Ghazali NA, Beard NA. Proteins within the intracellular calcium store determine cardiac RyR channel activity and cardiac output. Clin Exp Pharmacol Physiol 2013; 39:477-84. [PMID: 22524859 DOI: 10.1111/j.1440-1681.2012.05704.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
SUMMARY The contractile function of the heart requires the release of Ca(2+) from intracellular Ca(2+) stores in the sarcoplasmic reticulum (SR) of cardiac muscle cells. The efficacy of Ca(2+) release depends on the amount of Ca(2+) loaded into the Ca(2+) store and the way in which this 'Ca(2+) load' influences the activity of the cardiac ryanodine receptor Ca(2+) release channel (RyR2). The effects of the Ca(2+) load on Ca(2+) release through RyR2 are facilitated by: (i) the sensitivity of RyR2 itself to luminal Ca(2+) concentrations; and (ii) interactions between the cardiac Ca(2+) -binding protein calsequestrin (CSQ) 2 and RyR2, transmitted through the 'anchoring' proteins junctin and/or triadin. Mutations in RyR2 are linked to catecholaminergic polymorphic ventricular tachycardia (CPVT) and sudden cardiac death. The tachycardia is associated with changes in the sensitivity of RyR2 to luminal Ca(2+) . Triadin-, junctin- or CSQ-null animals survive, but their longevity and ability to tolerate stress is compromised. These studies reveal the importance of the proteins in normal muscle function, but do not reveal the molecular nature of their functional interactions, which must be defined before changes in the proteins leading to CPVT and heart disease can be understood. Herein, we discuss known interactions between the RyR, triadin, junctin and CSQ with emphasis on the cardiac isoforms of the proteins. Where there is little known about the cardiac isoforms, we discuss evidence from skeletal isoforms.
Collapse
|
42
|
Hanna AD, Lam A, Dulhunty AF, Beard NA. Anthracycline-Induced Dysfunction of Cardiac SR Ca2+ Handling - The Role of Thiol Oxidation. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
|
43
|
Willemse H, Smith PN, Board PG, Casarotto MG, Dulhunty AF. Human Aging and Expression of Proteins Interacting with the Ryanodine Receptor in Skeletal Muscle. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.612] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
|
44
|
Li L, Mirza S, Beard NA, Dulhunty AF. A Cytoplasmic Interaction between Junctin and RyRs with Major Consequences for RyR1 and RyR2 Activity In Vitro. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.611] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
|
45
|
Rebbeck RT, Willemse H, Groom L, Dirksen RT, Dulhunty AF. Interactions between Dihydropyridine β1A Subunit and Ryanodine Receptor Isoforms. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
|
46
|
Dulhunty AF, Beard NA, Hanna AD. Regulation and dysregulation of cardiac ryanodine receptor (RyR2) open probability during diastole in health and disease. ACTA ACUST UNITED AC 2012; 140:87-92. [PMID: 22851673 PMCID: PMC3409097 DOI: 10.1085/jgp.201210862] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
47
|
Karunasekara Y, Rebbeck RT, Weaver LM, Board PG, Dulhunty AF, Casarotto MG. An α-helical C-terminal tail segment of the skeletal L-type Ca2+ channel β1a subunit activates ryanodine receptor type 1 via a hydrophobic surface. FASEB J 2012; 26:5049-59. [PMID: 22962299 DOI: 10.1096/fj.12-211334] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Excitation-contraction (EC) coupling in skeletal muscle depends on protein interactions between the transverse tubule dihydropyridine receptor (DHPR) voltage sensor and intracellular ryanodine receptor (RyR1) calcium release channel. We present novel data showing that the C-terminal 35 residues of the β(1a) subunit adopt a nascent α-helix in which 3 hydrophobic residues align to form a hydrophobic surface that binds to RyR1 isolated from rabbit skeletal muscle. Mutation of the hydrophobic residues (L496, L500, W503) in peptide β(1a)V490-M524, corresponding to the C-terminal 35 residues of β(1a), reduced peptide binding to RyR1 to 15.2 ± 7.1% and prevented the 2.9 ± 0.2-fold activation of RyR1 by 10 nM wild-type peptide. An upstream hydrophobic heptad repeat implicated in β(1a) binding to RyR1 does not contribute to RyR1 activation. Wild-type β(1a)A474-A508 peptide (10 nM), containing heptad repeat and hydrophobic surface residues, increased RyR1 activity by 2.3 ± 0.2- and 2.2 ± 0.3-fold after mutation of the heptad repeat residues. We conclude that specific hydrophobic surface residues in the 35 residue β(1a) C-terminus bind to RyR1 and increase channel activity in lipid bilayers and thus may support skeletal EC coupling.
Collapse
|
48
|
Takano K, Liu D, Tarpey P, Gallant E, Lam A, Witham S, Alexov E, Chaubey A, Stevenson RE, Schwartz CE, Board PG, Dulhunty AF. An X-linked channelopathy with cardiomegaly due to a CLIC2 mutation enhancing ryanodine receptor channel activity. Hum Mol Genet 2012; 21:4497-507. [PMID: 22814392 DOI: 10.1093/hmg/dds292] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Chloride intracellular channel 2 (CLIC2) protein is a member of the glutathione transferase class of proteins. Its' only known function is the regulation of ryanodine receptor (RyR) intracellular Ca(2+) release channels. These RyR proteins play a major role in the regulation of Ca(2+) signaling in many cells. Utilizing exome capture and deep sequencing of genes on the X-chromosome, we have identified a mutation in CLIC2 (c.303C>G, p.H101Q) which is associated with X-linked intellectual disability (ID), atrial fibrillation, cardiomegaly, congestive heart failure (CHF), some somatic features and seizures. Functional studies of the H101Q variant indicated that it stimulated rather than inhibited the action of RyR channels, with channels remaining open for longer times and potentially amplifying Ca(2+) signals dependent on RyR channel activity. The overly active RyRs in cardiac and skeletal muscle cells and neuronal cells would result in abnormal cardiac function and trigger post-synaptic pathways and neurotransmitter release. The presence of both cardiomegaly and CHF in the two affected males and atrial fibrillation in one are consistent with abnormal RyR2 channel function. Since the dysfunction of RyR2 channels in the brain via 'leaky mutations' can result in mild developmental delay and seizures, our data also suggest a vital role for the CLIC2 protein in maintaining normal cognitive function via its interaction with RyRs in the brain. Therefore, our patients appear to suffer from a new channelopathy comprised of ID, seizures and cardiac problems because of enhanced Ca(2+) release through RyRs in neuronal cells and cardiac muscle cells.
Collapse
|
49
|
Liu D, Hewawasam R, Karunasekara Y, Casarotto MG, Dulhunty AF, Board PG. The inhibitory glutathione transferase M2-2 binding site is located in divergent region 3 of the cardiac ryanodine receptor. Biochem Pharmacol 2012; 83:1523-9. [PMID: 22406107 DOI: 10.1016/j.bcp.2012.02.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2011] [Revised: 02/19/2012] [Accepted: 02/21/2012] [Indexed: 10/28/2022]
Abstract
The muscle-specific glutathione transferase GSTM2-2 modulates the activity of ryanodine receptor (RyR) calcium release channels: it inhibits the activity of cardiac RyR (RyR2) channels with high affinity and activates skeletal RyR (RyR1) channels with low affinity. The C terminal domain of GSTM2-2 (GSTM2C) alone physically binds to RyR2 and inhibits its activity, but it does not bind to RyR1. We have now used yeast two-hybrid analysis, chemical cross-linking, intrinsic tryptophan fluorescence and Ca(2+) release studies to determine that the binding site for GSTM2C is in divergent region 3 (D3) of RyR2. The D3 region encompasses residues 1855-1890 in RyR2. Specific mutagenesis shows the binding primarily involves electrostatic interactions with residues K1875, K1886, R1887 and K1889, all residues that are present in RyR2, but not in RyR1. The significant sequence differences between the D3 regions of RyR2 and RyR1 explain why GSTM2-2 specifically inhibits RyR2. This specific inhibition of RyR2 could modulate Ca cycling and be useful for the treatment of heart failure. RyR2 inhibition during diastole may improve filling of the SR with Ca(2+) and improve contractility.
Collapse
|
50
|
Janczura M, Blackburn A, Dulhunty AF, Beard NA. Acute Chemotherapeutic Treatment Induces Chronic Phosphorylation of the Cardiac Ryanodine Receptor. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.3018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|