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Terrar DA. Timing mechanisms to control heart rhythm and initiate arrhythmias: roles for intracellular organelles, signalling pathways and subsarcolemmal Ca 2. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220170. [PMID: 37122228 PMCID: PMC10150226 DOI: 10.1098/rstb.2022.0170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2023] Open
Abstract
Rhythms of electrical activity in all regions of the heart can be influenced by a variety of intracellular membrane bound organelles. This is true both for normal pacemaker activity and for abnormal rhythms including those caused by early and delayed afterdepolarizations under pathological conditions. The influence of the sarcoplasmic reticulum (SR) on cardiac electrical activity is widely recognized, but other intracellular organelles including lysosomes and mitochondria also contribute. Intracellular organelles can provide a timing mechanism (such as an SR clock driven by cyclic uptake and release of Ca2+, with an important influence of intraluminal Ca2+), and/or can act as a Ca2+ store involved in signalling mechanisms. Ca2+ plays many diverse roles including carrying electric current, driving electrogenic sodium-calcium exchange (NCX) particularly when Ca2+ is extruded across the surface membrane causing depolarization, and activation of enzymes which target organelles and surface membrane proteins. Heart function is also influenced by Ca2+ mobilizing agents (cADP-ribose, nicotinic acid adenine dinucleotide phosphate and inositol trisphosphate) acting on intracellular organelles. Lysosomal Ca2+ release exerts its effects via calcium/calmodulin-dependent protein kinase II to promote SR Ca2+ uptake, and contributes to arrhythmias resulting from excessive beta-adrenoceptor stimulation. A separate arrhythmogenic mechanism involves lysosomes, mitochondria and SR. Interacting intracellular organelles, therefore, have profound effects on heart rhythms and NCX plays a central role. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.
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Affiliation(s)
- Derek A Terrar
- Department of Pharmacology, University of Oxford, Oxford OX1 3QT, UK
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Ju YK, Lee BH, Trajanovska S, Hao G, Allen DG, Lei M, Cannell MB. The involvement of TRPC3 channels in sinoatrial arrhythmias. Front Physiol 2015; 6:86. [PMID: 25859221 PMCID: PMC4373262 DOI: 10.3389/fphys.2015.00086] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 03/04/2015] [Indexed: 01/08/2023] Open
Abstract
Atrial fibrillation (AF) is a significant contributor to cardiovascular morbidity and mortality. The currently available treatments are limited and AF continues to be a major clinical challenge. Clinical studies have shown that AF is frequently associated with dysfunction in the sino-atrial node (SAN). The association between AF and SAN dysfunction is probably related to the communication between the SAN and the surrounding atrial cells that form the SAN-atrial pacemaker complex and/or pathological processes that affect both the SAN and atrial simultaneously. Recent evidence suggests that Ca2+ entry through TRPC3 (Transient Receptor Potential Canonical-3) channels may underlie several pathophysiological conditions -including cardiac arrhythmias. However, it is still not known if atrial and sinoatrial node cells are also involved. In this article we will first briefly review TRPC3 and IP3R signaling that relate to store/receptor-operated Ca2+ entry (SOCE/ROCE) mechanisms and cardiac arrhythmias. We will then present some of our recent research progress in this field. Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3−/− mice) compared to wild type controls. We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R. Activation of G-protein coupled receptors (GPCRs) signaling that is able to modulate SOCE/ROCE and Ang II induced Ca2+ homeostasis changes in sinoatrial complex being linked to TRPC3. The results provide new evidence that TRPC3 may play a role in sinoatrial and atrial arrhythmias that are caused by GPCRs activation.
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Affiliation(s)
- Yue-Kun Ju
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Bon Hyang Lee
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Sofie Trajanovska
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Gouliang Hao
- Department of Pharmacology, University of Oxford Oxford, UK
| | - David G Allen
- Department of Physiology, School of Medical Sciences, Bosch Institute, University of Sydney Sydney, NSW, Australia
| | - Ming Lei
- Department of Pharmacology, University of Oxford Oxford, UK
| | - Mark B Cannell
- Department of Physiology and Pharmacology, University of Bristol Bristol, UK
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Ju YK, Liu J, Lee BH, Lai D, Woodcock EA, Lei M, Cannell MB, Allen DG. Distribution and Functional Role of Inositol 1,4,5-
tris
phosphate Receptors in Mouse Sinoatrial Node. Circ Res 2011; 109:848-57. [DOI: 10.1161/circresaha.111.243824] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Yue-Kun Ju
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - Jie Liu
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - Bon Hyang Lee
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - Donna Lai
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - Elizabeth A. Woodcock
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - Ming Lei
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - Mark B. Cannell
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
| | - David G. Allen
- From the School of Medical Sciences and Bosch Institute (Y.K.J., J.L., B.H.L., D.L., D.G.A.), University of Sydney, Sydney, Australia; Baker IDI Heart and Diabetes Institute (E.A.W.), Melbourne, Australia; School of Biomedicine (M.L.), Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK; Department of Physiology and Pharmacology (M.B.C.), University of Bristol, Bristol, UK
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Ridley JM, Cheng H, Harrison OJ, Jones SK, Smith GL, Hancox JC, Orchard CH. Spontaneous frequency of rabbit atrioventricular node myocytes depends on SR function. Cell Calcium 2008; 44:580-91. [PMID: 18550162 DOI: 10.1016/j.ceca.2008.04.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 04/18/2008] [Accepted: 04/22/2008] [Indexed: 11/29/2022]
Abstract
Spontaneous Ca(2+) release from the sarcoplasmic reticulum (SR) appears to play an important role in cardiac sinoatrial node pacemaking. However, comparatively little is known about the role of intracellular Ca(2+) in the atrioventricular node (AVN). Intracellular Ca(2+) was therefore monitored in cells isolated from the rabbit AVN, using fluo-3 in conjunction with confocal microscopy. These cells displayed spontaneous Ca(2+) transients and action potentials. Ca(2+) transients were normally preceded by a small, slow increase (ramp) of intracellular Ca(2+) which was sometimes, but not always, accompanied by Ca(2+) sparks. During the Ca(2+) transient, intracellular [Ca(2+)] increased initially at the cell periphery and propagated inhomogeneously to the cell centre. The rate of spontaneous activity was decreased by ryanodine (1muM) and increased by isoprenaline (500nM); these changes were accompanied by a decrease and increase, respectively, in the slope of the preceding Ca(2+) ramp, with no significant change in Ca(2+) spark characteristics. Rapidly reducing bathing [Na(+)] inhibited spontaneous activity. These findings provide the first information on Ca(2+) handling at the sub-cellular level and link cellular Ca(2+) cycling to the genesis of spontaneous activity in the AVN.
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Affiliation(s)
- J M Ridley
- Department of Physiology & Pharmacology, Cardiovascular Research Laboratories, Bristol Heart Institute, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
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Ju YK, Chu Y, Chaulet H, Lai D, Gervasio OL, Graham RM, Cannell MB, Allen DG. Store-Operated Ca
2+
Influx and Expression of TRPC Genes in Mouse Sinoatrial Node. Circ Res 2007; 100:1605-14. [PMID: 17478725 DOI: 10.1161/circresaha.107.152181] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Store-operated Ca
2+
entry was investigated in isolated mouse sinoatrial nodes (SAN) dissected from right atria and loaded with Ca
2+
indicators. Incubation of the SAN in Ca
2+
-free solution caused a substantial decrease in resting intracellular Ca
2+
concentration ([Ca
2+
]
i
) and stopped pacemaker activity. Reintroduction of Ca
2+
in the presence of cyclopiazonic acid (CPA), a sarcoplasmic reticulum Ca
2+
pump inhibitor, led to sustained elevation of [Ca
2+
]
i
, a characteristic of store-operated Ca
2+
channel (SOCC) activity. Two SOCC antagonists, Gd
3+
and SKF-96365, inhibited 72±8% and 65±8% of this Ca
2+
influx, respectively. SKF-96365 also reduced the spontaneous pacemaker rate to 27±4% of control in the presence of CPA. Because members of the transient receptor potential canonical (TRPC) gene family may encode SOCCs, we used RT-PCR to examine mRNA expression of the 7 known mammalian TRPC isoforms. Transcripts for TRPC1, 2, 3, 4, 6, and 7, but not TRPC5, were detected. Immunohistochemistry using anti-TRPC1, 3, 4, and 6 antibodies revealed positive labeling in the SAN region and single pacemaker cells. These results indicate that mouse SAN exhibits store-operated Ca
2+
activity which may be attributable to TRPC expression, and suggest that SOCCs may be involved in regulating pacemaker firing rate.
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Affiliation(s)
- Yue-Kun Ju
- School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, NSW, Australia.
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Ju YK, Allen DG. Early effects of metabolic inhibition on intracellular Ca2+ in toad pacemaker cells: involvement of Ca2+ stores. Am J Physiol Heart Circ Physiol 2003; 284:H1087-94. [PMID: 12595299 DOI: 10.1152/ajpheart.00755.2002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The early effects of metabolic inhibition on intracellular Ca(2+) concentration ([Ca(2+)](i)), Ca(2+) current, and sarcoplasmic reticulum (SR) Ca(2+) content were studied in single pacemaker cells from the sinus venosus of the cane toad. The amplitude of the spontaneous elevations of systolic [Ca(2+)](i) (Ca(2+) transients) was reduced after 5-min exposure to 2 mM NaCN from 338 +/- 30 to 189 +/- 37 nM (P < 0.005, n = 9), and the spontaneous firing rate was reduced from 27 +/- 2 to 12 +/- 4 beats/min (P < 0.002, n = 9). It has been proposed that CN(-) acts by inhibition of cytochrome P-450, resulting in a reduction of cAMP and Ca(2+) current. To test this proposal, we used clotrimazole, a cytochrome P-450 inhibitor, which also decreased the Ca(2+) transients and firing rate. CN(-) caused an insignificant fall of Ca(2+) current (23 +/- 11%) but a substantial reduction of SR Ca(2+) content (by 65 +/- 5%), whereas clotrimazole produced a larger reduction of Ca(2+) current and did not affect the SR Ca(2+) content. Thus the main effect of CN(-) does not seem to be through inhibition of cytochrome P-450. In conclusion, CN(-) appears to reduce Ca(2+) release from the SR mainly by reducing SR Ca(2+) content. A likely cause of the decreased SR content is reduced Ca(2+) uptake by the SR pump.
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Affiliation(s)
- Yue-Kun Ju
- Department of Physiology and Institute for Biomedical Research, University of Sydney, New South Wales 2006, Australia
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