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Nielsen J, Johnsen J, Pryds K, Ørtenblad N, Bøtker HE. Myocardial subcellular glycogen distribution and sarcoplasmic reticulum Ca 2+ handling: effects of ischaemia, reperfusion and ischaemic preconditioning. J Muscle Res Cell Motil 2019; 42:17-31. [PMID: 31630282 DOI: 10.1007/s10974-019-09557-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 10/09/2019] [Indexed: 11/29/2022]
Abstract
Ischaemic preconditioning (IPC) protects against myocardial ischaemia-reperfusion injury. The metabolic and ionic effects of IPC remain to be clarified in detail. We aimed to investigate the effect of IPC (2 times 5 min ischaemia) on the subcellular distribution of glycogen and Ca2+-uptake and leakiness by the sarcoplasmic reticulum (SR) in response to ischaemia-reperfusion in cardiomyocytes of isolated perfused rat hearts (Wistar rats, 335 ± 25 g). As estimated by quantitative transmission electron microscopy, the pre-ischaemic contribution [%, mean (95% CI)] of three sub-fractions of glycogen relative to total glycogen was 50 (39:61) as subsarcolemmal, 41 (31:50) as intermyofibrillar, and 9 (5:13) as intramyofibrillar glycogen. After 25 min of ischaemia, the relative contribution (%) of subsarcolemmal glycogen decreased to 39 (32:47) in control hearts (Con) and to 38 (31:45) in IPC. After 15 min reperfusion the contribution of subsarcolemmal glycogen was restored to pre-ischaemic levels in IPC hearts, but not in Con hearts. IPC increased the left ventricular developed pressure following ischaemia-reperfusion compared with Con. In saponin-skinned cardiomyocyte bundles, ischaemia reduced the SR Ca2+-uptake rate, with no effect of IPC. However, IPC reduced a SR Ca2+-leakage at pre-ischaemia, after ischaemia and during reperfusion. In conclusion, subsarcolemmal glycogen was preferentially utilised during sustained myocardial ischaemia. IPC improved left ventricular function reflecting reduced ischaemia-reperfusion injury, mediated a re-distribution of glycogen towards a preferential storage within the subsarcolemmal space during reperfusion, and lowered SR Ca2+-leakage. Under the present conditions, we found no temporal associations between alterations in glycogen localisation and SR Ca2+ kinetics.
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Affiliation(s)
- Joachim Nielsen
- Department of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC), University of Southern Denmark, 5230, Odense M, Denmark.
| | - Jacob Johnsen
- Department of Cardiology, Aarhus University Hospital, 8200, Aarhus N, Denmark
| | - Kasper Pryds
- Department of Cardiology, Aarhus University Hospital, 8200, Aarhus N, Denmark
| | - Niels Ørtenblad
- Department of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC), University of Southern Denmark, 5230, Odense M, Denmark
| | - Hans Erik Bøtker
- Department of Cardiology, Aarhus University Hospital, 8200, Aarhus N, Denmark
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Stewart R, Song L, Carter SM, Sigalas C, Zaccai NR, Kanamarlapudi V, Bhat MB, Takeshima H, Sitsapesan R. Single-channel characterization of the rabbit recombinant RyR2 reveals a novel inactivation property of physiological concentrations of ATP. J Membr Biol 2008; 222:65-77. [PMID: 18418540 DOI: 10.1007/s00232-008-9102-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2008] [Accepted: 03/05/2008] [Indexed: 10/22/2022]
Abstract
Ryanodine receptor 2 (RyR2) cDNA has been available for more than 15 years; however, due to the complex nature of ligand gating in this channel, many aspects of recombinant RyR2 function have been unresearched. We established a stable, inducible HEK 293 cell line expressing full-length rabbit RyR2 cDNA and assessed the single-channel properties of the recombinant RyR2, with particular reference to ligand regulation with Ca2+ as the permeant ion. We found that the single-channel conductances of recombinant RyR2 and RyR2 isolated from cardiac muscle are essentially identical, as is irreversible modification by ryanodine. Although it is known that RyR2 expressed in HEK 293 cells is not associated with FKBP12.6, we demonstrate that these channels do not exhibit any discernable disorganized gating characteristics or subconductance states. We also show that the gating of recombinant RyR2 is indistinguishable from that of channels isolated from cardiac muscle when activated by cytosolic Ca2+, caffeine or suramin. The mechanisms underlying ATP activation are also similar; however, the experiments highlighted a novel effect of ATP at physiologically relevant concentrations of 5-10 mM. With Ca2+ as permeant ion, 5-10 mM ATP consistently inactivated recombinant channels (15/16 experiments). Such inactivation was rarely observed with native RyR2 isolated from cardiac muscle (1 in 16 experiments). However, if the channels were purified, inactivation by ATP was then revealed in all experiments. This action of ATP may be relevant for inactivation of sarcoplasmic reticulum Ca2+ release during cardiac excitation-contraction coupling or may represent unnatural behavior that is revealed when RyR2 is purified or expressed in noncardiac systems.
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Affiliation(s)
- Richard Stewart
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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Dhalla NS, Saini HK, Tappia PS, Sethi R, Mengi SA, Gupta SK. Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease. J Cardiovasc Med (Hagerstown) 2007; 8:238-50. [PMID: 17413299 DOI: 10.2459/01.jcm.0000263489.13479.68] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.
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Affiliation(s)
- Naranjan S Dhalla
- Institute of Cardiovascular Sciences, St Boniface General Hospital Research Centre, and Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
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Dumitrescu C, Narayan P, Efimov IR, Cheng Y, Radin MJ, McCune SA, Altschuld RA. Mechanical alternans and restitution in failing SHHF rat left ventricles. Am J Physiol Heart Circ Physiol 2002; 282:H1320-6. [PMID: 11893567 DOI: 10.1152/ajpheart.00466.2001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined mechanical alternans and electromechanical restitution in normal and failing rat hearts. Alternans occurred at 5 Hz in failing versus 9 Hz in control hearts and was reversed by 300 nM isoproterenol, 6 mM extracellular Ca(2+), 300 nM -BAY K 8644, or 50 nM ryanodine. Restitution curves comprised phase I, which was completed before relaxation of the steady-state beat, and phase II, which occurred later. Phase I action potential area and developed pressure ratios were significantly reduced in the failing versus control hearts. Phase II was a monoexponential increase in relative developed pressure as the extrasystolic interval was increased. The plateau of phase II was significantly elevated in failing hearts. Thapsigargin (3 microM) plus ryanodine (200 nM) potentiated phase I to a significantly greater extent in control versus failing hearts and abolished phase II in both groups. The results suggest that both regulation of Ca(2+) influx across the sarcolemma and Ca(2+) release by the sarcoplasmic reticulum may contribute to altered excitation-contraction coupling in the failing spontaneously hypertensive heart failure prone rat heart.
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Affiliation(s)
- Cristian Dumitrescu
- The Ohio State University Biophysics Program and Dorothy M. Davis Heart and Lung Research Institute, Columbus 43210, USA
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5
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Menshikova EV, Salama G. Cardiac ischemia oxidizes regulatory thiols on ryanodine receptors: captopril acts as a reducing agent to improve Ca2+ uptake by ischemic sarcoplasmic reticulum. J Cardiovasc Pharmacol 2000; 36:656-68. [PMID: 11065227 DOI: 10.1097/00005344-200011000-00016] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
We tested the hypothesis that ischemia alters sarcoplasmic reticulum (SR) Ca2+ transport by oxidizing regulatory thiols on ryanodine receptors (RyRs), and that membrane-permeable sulfhydryl-containing angiotensin-converting enzyme (ACE) inhibitors protect against ischemia-induced oxidation and explain in part, the therapeutic actions of captopril. Ca2+ uptake and adenosine triphosphatase (ATPase) activity was measured from SR vesicles isolated from control or ischemic dog and human ventricles and compared with or without sulfhydryl reductants. The rate and amount of Ca2+ uptake was lower for canine ischemic SR compared with control (6.5 +/- 0.2 --> 18.5 +/- 1.1 nmol Ca2+/mg/min and 123.1 +/- 4.7 --> 235.0 +/- 17.3 nmol Ca2+/mg; n = 8 each). Captopril, dithiothreitol (DTT), glutathione (GSH), and L-cysteine increased the rate and amount of Ca2+ uptake by canine and human ischemic SR vesicles by approximately 50%. Reducing agents had no effect on Ca2+- ATPase activity in either canine control or ischemic (approximately 40% less than control) SR. Captopril was as potent as DTT at reversing the oxidation of skeletal and cardiac RyRs induced by reactive disulfides (RDSs) or nitric oxide (NO). In neonatal rat myocytes, RDSs or NO triggered SR Ca2+ release and increased cytosolic Ca2+, an effect reversed by captopril and DTT but not GSH or cysteine. Pretreatment of myocytes with captopril (exposure and then wash) inhibited Ca2+ elevation elicited by RDSs or NO, indicating that captopril is an effective, membrane-permeable intracellular reducing agent. Thus, net SR Ca2+ accumulation is reduced by ischemia in part due to the oxidation of thiols that gate RyRs, an effect reversed by captopril.
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Affiliation(s)
- E V Menshikova
- Department of Cell Biology and Physiology, University of Pittsburgh, School of Medicine, Pennsylvania 15261, USA
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Ching LL, Williams AJ, Sitsapesan R. AMP is a partial agonist at the sheep cardiac ryanodine receptor. Br J Pharmacol 1999; 127:161-71. [PMID: 10369469 PMCID: PMC1565978 DOI: 10.1038/sj.bjp.0702491] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
We have investigated the ability of AMP to modulate the native sheep cardiac ryanodine receptor (RyR) channel at various cytosolic [Ca2+]. Channels were incorporated into planar phospholipid bilayers and current fluctuations through the bilayer were monitored under voltage clamp conditions. We demonstrate that AMP only exhibits agonist activity if the cytosolic [Ca2+] is sufficiently high. Even in the presence of a high cytosolic [Ca2+] (65 microM), AMP cannot fully open the channel and the maximum open probability (Po) observed is approximately 0.3 at 2 mM AMP. Concentrations of AMP above the maximally activating level cause inactivation of the channel. Our experiments indicate that AMP is an agonist with such low efficacy at the ATP sites on the cardiac RyR that it is effectively an antagonist of ATP-induced increases in Po. Our study demonstrates that the number of phosphates attached to the 5'-carbon of the ribose ring of adenine-based compounds determines the efficacy of the ligand to increase the Po of the cardiac RyR. Substitution of groups at this position may lead to the identification of potent antagonists at ATP sites on RyR.
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Affiliation(s)
- Li Lien Ching
- Cardiac Medicine, Imperial College School of Medicine, Dovehouse Street, London SW3 6LY
| | - Alan J Williams
- Cardiac Medicine, Imperial College School of Medicine, Dovehouse Street, London SW3 6LY
| | - Rebecca Sitsapesan
- Cardiac Medicine, Imperial College School of Medicine, Dovehouse Street, London SW3 6LY
- Author for correspondence:
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Xu L, Meissner G. Regulation of cardiac muscle Ca2+ release channel by sarcoplasmic reticulum lumenal Ca2+. Biophys J 1998; 75:2302-12. [PMID: 9788925 PMCID: PMC1299904 DOI: 10.1016/s0006-3495(98)77674-x] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023] Open
Abstract
The cardiac muscle sarcoplasmic reticulum Ca2+ release channel (ryanodine receptor) is a ligand-gated channel that is activated by micromolar cytoplasmic Ca2+ concentrations and inactivated by millimolar cytoplasmic Ca2+ concentrations. The effects of sarcoplasmic reticulum lumenal Ca2+ on the purified release channel were examined in single channel measurements using the planar lipid bilayer method. In the presence of caffeine and nanomolar cytosolic Ca2+ concentrations, lumenal-to-cytosolic Ca2+ fluxes >/=0.25 pA activated the channel. At the maximally activating cytosolic Ca2+ concentration of 4 microM, lumenal Ca2+ fluxes of 8 pA and greater caused a decline in channel activity. Lumenal Ca2+ fluxes primarily increased channel activity by increasing the duration of mean open times. Addition of the fast Ca2+-complexing buffer 1,2-bis(2-aminophenoxy)ethanetetraacetic acid (BAPTA) to the cytosolic side of the bilayer increased lumenal Ca2+-activated channel activities, suggesting that it lowered Ca2+ concentrations at cytosolic Ca2+-inactivating sites. Regulation of channel activities by lumenal Ca2+ could be also observed in the absence of caffeine and in the presence of 5 mM MgATP. These results suggest that lumenal Ca2+ can regulate cardiac Ca2+ release channel activity by passing through the open channel and binding to the channel's cytosolic Ca2+ activation and inactivation sites.
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Affiliation(s)
- L Xu
- Department of Biochemistry & Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA
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Xu L, Tripathy A, Pasek DA, Meissner G. Potential for pharmacology of ryanodine receptor/calcium release channels. Ann N Y Acad Sci 1998; 853:130-48. [PMID: 10603942 DOI: 10.1111/j.1749-6632.1998.tb08262.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Calcium release channels, known also as ryanodine receptors (RyRs), play an important role in Ca2+ signaling in muscle and nonmuscle cells by releasing Ca2+ from intracellular stores. Mammalian tissues express three different RyR isoforms comprising four 560-kDa (RyR polypeptide) and four 12-kDa (FK506 binding protein) subunits. The large protein complexes conduct monovalent and divalent cations and are capable of multiple interactions with other molecules. The latter include small diffusible endogenous effector molecules including Ca2+, Mg2+, adenine nucleotides, sufhydryl modifying reagents (glutathione, NO, and NO adducts) and lipid intermediates, and proteins such as protein kinases and phosphatases, calmodulin, immunophilins (FK506 binding proteins), and in skeletal muscle the dihydropyridine receptor. Because of their role in regulating intracellular Ca2+ levels and their multiple ligand interactions, RyRs constitute an important, potentially rich pharmacological target for controlling cellular functions. Exogenous effectors found to affect RyR function include ryanoids, toxins, xanthines, anthraquinones, phenol derivatives, adenosine and purinergic agonists and antagonists, NO donors, oxidizing reagents, dantrolene, local anesthetics, and polycationic reagents.
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Affiliation(s)
- L Xu
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill 27599-7260, USA
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9
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Kermode H, Williams AJ, Sitsapesan R. The interactions of ATP, ADP, and inorganic phosphate with the sheep cardiac ryanodine receptor. Biophys J 1998; 74:1296-304. [PMID: 9512027 PMCID: PMC1299477 DOI: 10.1016/s0006-3495(98)77843-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The effects of ATP, ADP, and inorganic phosphate (Pi) on the gating of native sheep cardiac ryanodine receptor channels incorporated into planar phospholipid bilayers were investigated. We demonstrate that ATP and ADP can activate the channel by Ca2+-dependent and Ca2+-independent mechanisms. ATP and ADP appear to compete for the same site/s on the cardiac ryanodine receptor, and in the presence of cytosolic Ca2+ both agents tend to inactivate the channel at supramaximal concentrations. Our results reveal that ATP not only has a greater affinity for the adenine nucleotide site/s than ADP, but also has a greater efficacy. The EC50 value for channel activation is approximately 0.2 mM for ATP compared to 1.2 mM for ADP. Most interesting is the fact that, even in the presence of cytosolic Ca2+, ADP cannot activate the channel much above an open probability (Po) of 0.5, and therefore acts as a partial agonist at the adenine nucleotide binding site on the channel. We demonstrate that Pi also increases Po in a concentration and Ca2+-dependent manner, but unlike ATP and ADP, has no effect in the absence of activating cytosolic [Ca2+]. We demonstrate that Pi does not interact with the adenine nucleotide site/s but binds to a distinct domain on the channel to produce an increase in Po.
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Affiliation(s)
- H Kermode
- Imperial College School of Science, Technology and Medicine, Cardiac Medicine, London, United Kingdom
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10
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Liu W, Pasek DA, Meissner G. Modulation of Ca(2+)-gated cardiac muscle Ca(2+)-release channel (ryanodine receptor) by mono- and divalent ions. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C120-8. [PMID: 9458720 DOI: 10.1152/ajpcell.1998.274.1.c120] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The effects of mono- and divalent ions on Ca(2+)-gated cardiac muscle Ca(2+)-release channel (ryanodine receptor) activity were examined in [3H]ryanodine-binding measurements. Ca2+ bound with the highest apparent affinity to Ca2+ activation sites in choline chloride medium, followed by KCl, CsCl, NaCl, and LiCl media. The apparent Ca2+ binding affinities of Ca2+ inactivation sites were lower in choline chloride and CsCl media than in LiCl, NaCl, and KCl media. Sr2+ activated the ryanodine receptor with a lower efficacy than Ca2+. Competition studies indicated that Li+, K+, Mg2+, and Ba2+ compete with Ca2+ for Ca2+ activation sites. In 0.125 M KCl medium, the Ca2+ dependence of [3H]ryanodine binding was modified by 5 mM Mg2+ and 5 mM beta,gamma-methyleneadenosine 5'-triphosphate (a nonhydrolyzable ATP analog). The addition of 5 mM glutathione was without appreciable effect. Substitution of Cl- by 2-(N-morpholino)ethanesulfonic acid ion caused an increase in the apparent Ca2+ affinity of the Ca2+ inactivation sites, whereas an increase in KCl concentration had the opposite effect. These results suggest that cardiac muscle ryanodine receptor activity may be regulated by 1) competitive binding of mono- and divalent cations to Ca2+ activation sites, 2) binding of monovalent cations to Ca2+ inactivation sites, and 3) binding of anions to anion regulatory sites.
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Affiliation(s)
- W Liu
- Department of Physiology, University of North Carolina, Chapel Hill 27599-7260, USA
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Lammerich A, Bohm J, Schimke I, Wagner KD, Storch E, Günther J. Effects of hypoxia, simulated ischemia and reoxygenation on the contractile function of human atrial trabeculae. Mol Cell Biochem 1996; 160-161:143-51. [PMID: 8901468 DOI: 10.1007/bf00240044] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Hypoxia, ischemia and reoxygenation cause contractile dysfunction which will be characterized by the time course of isometric contraction of human atrial trabeculae. Post-rest potentiation (PRP) and postextrastimulatory potentiation (PEP) were elicited to obtain indirect information about the the role of the sarcoplasmic reticulum (SR) in excitation-contraction coupling. As lipid peroxidation could cause SR dysfunction, thiobarbituric acid reactive substances (TBARS) were measured. After 30 min of hypoxia (H) or simulated ischemia (H combined with acidosis-SI), contractile force decreased to 15% and 6%, respectively, of control (p < or = 0.05), whereas the normalized rate of both contraction and relaxation increased. In group H, rapid reoxygenation produced a recovery of contractile force to about 60%. After post-hypoxic reoxygenation the TBARS concentration was increased. In group SI, rapid reoxygenation and a rather gradual correction of acidosis produced complete recovery of contractile force. PRP and PEP were maintained during H and SI. Particularly post-ischemic reoxygenation caused a marked depression of PRP and partly of PEP. Thus, alteration of SR Ca2+ handling occurs predominantly during reoxygenation rather than during H or SI, probably associated with the damaging effect of increased oxygen radicals. The depression of potentiation occurred along with delayed relaxation, temporary increased resting force, mechanical alternans, and spontaneous activity which are further characteristics for SR dysfunction. Thus, for a possibly beneficial effect of low pH during SI combined with its gradual correction during reoxygenation on the recovery of contractile function, developed force should not be the only index.
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Affiliation(s)
- A Lammerich
- Institute of Physiology, Humboldt-University, Berlin, Germany
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Narayan P, McCune SA, Robitaille PM, Hohl CM, Altschuld RA. Mechanical alternans and the force-frequency relationship in failing rat hearts. J Mol Cell Cardiol 1995; 27:523-30. [PMID: 7760372 DOI: 10.1016/s0022-2828(08)80047-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
We examined contractile performance in perfused ventricles from normal rats and from SHHF/Mccfacp rats with end-stage heart failure. Changes in pacing frequency from 3 to 5 Hz evoked a complex response in normal rat myocardium. The first beat after a switch to 5 Hz was extremely weak, but each successive beat was stronger until force exceeded the 3 Hz steady state value by approximately 30%. Force then gradually declined to a new steady state where developed pressure was depressed but rate-pressure product was slightly greater than that at 3 Hz. By contrast, in failing SHHF/Mcc-facp hearts, an increase in pacing frequency from 3 to 5 Hz did not increase force development. Instead, the isovolumic left ventricles exhibited mechanical alternans. This alternation between weak and strong beats was abolished by 1 mM caffeine but restored by its washout. Inhibition of SR Ca2+ accumulation by 50-500 nM thapsigargin in normal ventricles did not evoke alternans when pacing frequencies were increased. The results indicate that mechanical alternans in failing rat hearts is due to altered reactions of the sarcoplasmic reticulum, but a decreased rate of Ca2+ accumulation is not the primary cause.
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Affiliation(s)
- P Narayan
- Ohio State University Departments' of Medical Biochemistry, Columbus 43210, USA
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