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Wang R, Wang M, Zhou J, Dai Z, Sun G, Sun X. Calenduloside E suppresses calcium overload by promoting the interaction between L-type calcium channels and Bcl2-associated athanogene 3 to alleviate myocardial ischemia/reperfusion injury. J Adv Res 2020; 34:173-186. [PMID: 35024189 PMCID: PMC8655133 DOI: 10.1016/j.jare.2020.10.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 10/22/2020] [Accepted: 10/26/2020] [Indexed: 01/12/2023] Open
Abstract
Introduction Intracellular calcium overload is an important contributor to myocardial ischemia/reperfusion (MI/R) injury. Total saponins of the traditional Chinese medicinal plant Aralia elata (Miq.) Seem. (AS) are beneficial for treating MI/R injury, and Calenduloside E (CE) is the main active ingredient of AS. Objectives This study aimed to investigate the effects of CE on MI/R injury and determine its specific regulatory mechanisms. Methods To verify whether CE mediated cardiac protection in vivo and in vitro, we performed MI/R surgery in SD rats and subjected neonatal rat ventricular myocytes (NRVMs) to hypoxia-reoxygenation (HR). CE’s cardioprotective against MI/R injury was detected by Evans blue/TTC staining, echocardiography, HE staining, myocardial enzyme levels. Impedance and field potential recording, and patch-clamp techniques of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were used to detect the function of L-type calcium channels (LTCC). The mechanisms underlying between CE and LTCC was studied through western blot, immunofluorescence, and immunohistochemistry. Drug affinity responsive target stability (DARTS) and co-immunoprecipitation (co-IP) used to further clarify the effect of CE on LTCC and BAG3. Results We found that CE protected against MI/R injury by inhibiting calcium overload. Furthermore, CE improved contraction and field potential signals of hiPSC-CMs and restored sarcomere contraction and calcium transient of adult rat ventricular myocytes (ARVMs). Moreover, patch-clamp data showed that CE suppressed increased L-type calcium current (ICa,L) caused by LTCC agonist, proving that CE could regulate calcium homeostasis through LTCC. Importantly, we found that CE promoted the interaction between LTCC and Bcl2-associated athanogene 3 (BAG3) by co-IP and DARTS. Conclusion Our results demonstrate that CE enhanced LTCC-BAG3 interaction to reduce MI/R induced-calcium overload, exerting a cardioprotective effect.
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Affiliation(s)
- Ruiying Wang
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.,Beijing Key Laboratory of Innovative Drug Discovery of Traditional Chinese Medicine (Natural Medicine) and Translational Medicine, Institute of Medicinal Plant Development, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing 100193, China.,Key Laboratory of New Drug Discovery Based on Classic Chinese Medicine Prescription, Chinese Academy of Medical Sciences, Beijing 100193, China
| | - Min Wang
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.,Beijing Key Laboratory of Innovative Drug Discovery of Traditional Chinese Medicine (Natural Medicine) and Translational Medicine, Institute of Medicinal Plant Development, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing 100193, China.,Key Laboratory of New Drug Discovery Based on Classic Chinese Medicine Prescription, Chinese Academy of Medical Sciences, Beijing 100193, China
| | - Jiahui Zhou
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.,Beijing Key Laboratory of Innovative Drug Discovery of Traditional Chinese Medicine (Natural Medicine) and Translational Medicine, Institute of Medicinal Plant Development, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing 100193, China.,Key Laboratory of New Drug Discovery Based on Classic Chinese Medicine Prescription, Chinese Academy of Medical Sciences, Beijing 100193, China
| | - Ziru Dai
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.,Beijing Key Laboratory of Innovative Drug Discovery of Traditional Chinese Medicine (Natural Medicine) and Translational Medicine, Institute of Medicinal Plant Development, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing 100193, China.,Key Laboratory of New Drug Discovery Based on Classic Chinese Medicine Prescription, Chinese Academy of Medical Sciences, Beijing 100193, China
| | - Guibo Sun
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.,Beijing Key Laboratory of Innovative Drug Discovery of Traditional Chinese Medicine (Natural Medicine) and Translational Medicine, Institute of Medicinal Plant Development, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing 100193, China.,Key Laboratory of New Drug Discovery Based on Classic Chinese Medicine Prescription, Chinese Academy of Medical Sciences, Beijing 100193, China
| | - Xiaobo Sun
- Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.,Beijing Key Laboratory of Innovative Drug Discovery of Traditional Chinese Medicine (Natural Medicine) and Translational Medicine, Institute of Medicinal Plant Development, Peking Union Medical College & Chinese Academy of Medical Sciences, Beijing 100193, China.,Key Laboratory of New Drug Discovery Based on Classic Chinese Medicine Prescription, Chinese Academy of Medical Sciences, Beijing 100193, China
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Dick IE, Joshi-Mukherjee R, Yang W, Yue DT. Arrhythmogenesis in Timothy Syndrome is associated with defects in Ca(2+)-dependent inactivation. Nat Commun 2016; 7:10370. [PMID: 26822303 PMCID: PMC4740114 DOI: 10.1038/ncomms10370] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Accepted: 12/03/2015] [Indexed: 12/18/2022] Open
Abstract
Timothy Syndrome (TS) is a multisystem disorder, prominently featuring cardiac action potential prolongation with paroxysms of life-threatening arrhythmias. The underlying defect is a single de novo missense mutation in CaV1.2 channels, either G406R or G402S. Notably, these mutations are often viewed as equivalent, as they produce comparable defects in voltage-dependent inactivation and cause similar manifestations in patients. Yet, their effects on calcium-dependent inactivation (CDI) have remained uncertain. Here, we find a significant defect in CDI in TS channels, and uncover a remarkable divergence in the underlying mechanism for G406R versus G402S variants. Moreover, expression of these TS channels in cultured adult guinea pig myocytes, combined with a quantitative ventricular myocyte model, reveals a threshold behaviour in the induction of arrhythmias due to TS channel expression, suggesting an important therapeutic principle: a small shift in the complement of mutant versus wild-type channels may confer significant clinical improvement. Timothy Syndrome (TS) is a multisystem disorder caused by two mutations leading to dysfunction of the CaV1.2 channel. Here, Dick et al. uncover a major and mechanistically divergent effect of both mutations on Ca2+/calmodulin-dependent inactivation of CaV1.2 channels, suggesting genetic variant-tailored therapy for TS treatment.
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Affiliation(s)
- Ivy E Dick
- Calcium Signals Laboratory, Departments of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Ross Building, Room 713, 720 Rutland Avenue, Baltimore, Maryland 21205, USA
| | - Rosy Joshi-Mukherjee
- Calcium Signals Laboratory, Departments of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Ross Building, Room 713, 720 Rutland Avenue, Baltimore, Maryland 21205, USA
| | - Wanjun Yang
- Calcium Signals Laboratory, Departments of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Ross Building, Room 713, 720 Rutland Avenue, Baltimore, Maryland 21205, USA
| | - David T Yue
- Calcium Signals Laboratory, Departments of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Ross Building, Room 713, 720 Rutland Avenue, Baltimore, Maryland 21205, USA
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Sharma N, Bhattarai JP, Hwang PH, Han SK. Nitric oxide suppresses L-type calcium currents in basilar artery smooth muscle cells in rabbits. Neurol Res 2013; 35:424-8. [PMID: 23540411 DOI: 10.1179/1743132812y.0000000129] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
OBJECTIVES Nitric oxide (NO) is well known to be a vasodilator, and NO donor compounds are currently used for treating vasospasm following subarachnoid hemorrhage. However, the action mechanism of cerebral vascular relaxation is not yet clear. L-type calcium channels have been determined to play an essential role in smooth muscle contraction. To investigate the role of L-type calcium channels in NO-induced relaxation of basilar smooth muscle cells, we examined the effect of the NO donor, sodium nitroprusside (SNP) on calcium (Ca2+) currents using smooth muscle cells isolated from a rabbit basilar artery. METHOD The smooth muscle cells were isolated from rabbit basilar artery by enzyme treatment. To identify L-type Ca2+ currents, we used cesium chloride, a potassium channel blocker and Bay K8644, an activator of L-type Ca2+ channel. RESULTS The L-type calcium currents (91±13.0 pA; n = 11) were significantly reduced by SNP (32±5 pA; n = 11; P<0.05). 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one, a 3',5'-cyclic guanosine monophosphate inhibitor, blocked the effect of SNP on L-type Ca2+ currents, and similar results were obtained after the application of 7-nitroindazole, a specific NO synthase inhibitor. Furthermore, inward currents were enhanced by Bay K8644 (170±22 pA; n = 5) and were suppressed by SNP (54±13 pA; n = 5; P<0.05). DISCUSSION These results demonstrate that NO suppresses the L-type Ca2+ currents in rabbit basilar smooth muscle cells, and suggest that L-type Ca2+ channels may play a pivotal role in NO-induced vascular relaxation.
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Affiliation(s)
- Naveen Sharma
- Department of Pediatrics & Research Institute of Clinical Medicine, School of Medicine, Chonbuk National University, Jeonju, Korea
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4
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Abstract
We have developed a model for the rat phrenic motor neuron (PMN) that robustly replicates many experimentally observed behaviors of PMNs in response to pharmacological, ionic, and electrical perturbations using a single set of parameters. Our model suggests that the after-depolarization (ADP) response seen in action potentials is a result of the slow deactivation of the fast sodium channel in the range of the ADP coupled with the activation of the L-type calcium channel (I(CaL)). This current and its interactions with the small and large conductance calcium-activated potassium currents (I(KCaSK) and I(KCaBK), respectively) is also important in the generation of spike frequency adaptation in the repetitive firing mode of activity. Other aspects of the model conform very well to experimental observations in both the action potential and repetitive firing mode of activity, including the role of I(KCaSK) in the medium after-hyperpolarization (AHP) and the role of I(KCaBK) in the fast AHP. We have made a number of predictions using the model, including the characterization of two putative sodium currents (fast and persistent), as well as functional roles for the N- and T-type calcium currents.
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Affiliation(s)
- Behrang Amini
- Department of Neurobiology and Anatomy, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
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5
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Abstract
We endeavor to show that the metabolism of the nonbeating heart can vary over an extreme range: from values approximating those measured in the beating heart to values of only a small fraction of normal--perhaps mimicking the situation of nonflow arrest during cardiac bypass surgery. We discuss some of the technical issues that make it difficult to establish the magnitude of basal metabolism in vivo. We consider some of the likely contributors to its magnitude and point out that the biochemical reasons for a sizable fraction of the heart's basal ATP usage remain unresolved. We consider many of the physiological factors that can alter the basal metabolic rate, stressing the importance of substrate supply. We point out that the protective effect of hypothermia may be less than is commonly assumed in the literature and suggest that hypoxia and ischemia may be able to regulate basal metabolic rate, thus making an important contribution to the phenomenon of cardiac hibernation.
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Affiliation(s)
- C L Gibbs
- Department of Physiology, Faculty of Medicine, Nursing and Health Sciences, Monash University, PO Box 13F, Monash University, Victoria 3800, Australia.
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6
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Li B, Chik CL, Ho AK, Karpinski E. L-type Ca(2+) channel regulation by pituitary adenylate cyclase-activating polypeptide in vascular myocytes from spontaneously hypertensive rats. Endocrinology 2001; 142:2865-73. [PMID: 11416005 DOI: 10.1210/endo.142.7.8229] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP), a vasoactive peptide, modulates the L-type Ca(2+) channel current (L channel current) in vascular smooth muscle cells (VSMC) through activation and integration of two intracellular pathways, protein kinase A and protein kinase C (PKC). In the present study we compared the effects of PACAP on the L channel current in VSMC from the spontaneously hypertensive rats (SHR) and normotensive controls, Wistar Kyoto rats (WKY). We found that compared with WKY, VSMC from SHR had a higher L channel current density. Stimulation by PACAP (10 nM) caused an increase in the amplitude of the whole cell current and prolonged open time in VSMC from SHR and WKY, with the increase greater in SHR. These effects of PACAP on the L channel current was mimicked by an activator of PKC. In contrast, PACAP caused a smaller increase in cAMP accumulation in VSMC from SHR than WKY, and there was no difference in the inhibitory effect of 8-bromo-cAMP on the L channel current from both type of cells. The greater increase in amplitude of the L channel current by PACAP in VSMC from SHR persisted in the presence of adenosine cyclic 3',5'-monophosphothioate, Rp-isomer, a cAMP antagonist, but not calphostin C, a PKC inhibitor. Taken together, our results show an increase in L channel current density and an enhanced PACAP effect on the L channel current in VSMC from SHR compared with WKY. This difference in PACAP response appears to be predominately secondary to an increased PKC sensitivity.
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MESH Headings
- Animals
- Arteries
- Calcium Channels, L-Type/drug effects
- Calcium Channels, L-Type/physiology
- Cyclic AMP-Dependent Protein Kinases/physiology
- Electric Conductivity
- Hypertension/physiopathology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Muscle, Smooth, Vascular/pathology
- Neuropeptides/pharmacology
- Neuropeptides/physiology
- Pituitary Adenylate Cyclase-Activating Polypeptide
- Protein Kinase C/physiology
- Rats
- Rats, Inbred SHR/physiology
- Rats, Inbred WKY
- Reference Values
- Tail/blood supply
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Affiliation(s)
- B Li
- Departments of Physiology and Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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7
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Nakayama S, Klugbauer N, Kabeya Y, Smith LM, Hofmann F, Kuzuya M. The alpha 1-subunit of smooth muscle Ca(2+) channel preserves multiple open states induced by depolarization. J Physiol 2000; 526 Pt 1:47-56. [PMID: 10878098 PMCID: PMC2270004 DOI: 10.1111/j.1469-7793.2000.00047.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The cloned alpha 1-subunits of the smooth muscle Ca(2+) channel (alpha (1C-b)) from rabbit lung were expressed in Chinese hamster ovary cells. The effect of large depolarizations was examined using cell-attached patch clamp techniques. After large, long-duration depolarizations (to +80 mV, 4 s), the cloned smooth muscle Ca(2+) channels were still open, and also showed slow channel closure upon repolarization. The sum of unitary channel currents revealed that the tail current seen after large conditioning depolarizations had a slower deactivation time constant compared to that seen when the cell membrane was depolarized briefly with a test step (to +40 mV), suggesting that large depolarizations transform the conformation of the Ca(2+) channels to a second open state. The decay time course of the tail current induced by large conditioning depolarizations was prolonged by reducing the negativity of the repolarization step, and vice versa. Using the slow deactivating characteristic, the current-voltage relationship was directly measured by applying a ramp pulse after a large depolarization. Its slope conductance was approximately 26 pS. Since the patch pipettes contained Ca(2+) agonists, the transition of the Ca(2+) channel conformation to the second, long open state during a large depolarization was distinct from that caused by Ca(2+) agonists, suggesting that the cloned alpha 1-subunits of smooth muscle Ca(2+) channels preserve the characteristic features seen in native smooth muscle Ca(2+) channels. In addition, when skeletal muscle beta-subunits were coexpressed with the alpha 1-subunits, the long channel openings after large, long-duration depolarizations were frequently suppressed. This phenomenon could be explained if the skeletal muscle beta-subunits increased the inactivation rate during the preconditioning depolarization.
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Affiliation(s)
- S Nakayama
- Department of Physiology, School of Medicine, Nagoya University, Nagoya 466, Japan.
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8
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Abstract
Hormones and neurotransmitters have both short-term and long-term modulatory effects on the activity of voltage-gated Ca2+ channels. Although much is known about the signal transduction underlying short-term modulation, there is far less information on mechanisms that produce long-term effects. Here, the molecular basis of long-lasting suppression of Ca2+ channel current in pituitary melanotropes by chronic dopamine exposure is examined. Experiments involving in vivo and in vitro treatments with the dopaminergic drugs haloperidol, bromocriptine, and quinpirole show that D2 receptors persistently decrease alpha1D L-type Ca2+ channel mRNA and L-type Ca2+ channel current without altering channel gating properties. In contrast, another L-channel (alpha1C) mRNA and P/Q-channel (alpha1A) mRNA are unaffected. The downregulation of alpha1D mRNA does not require decreases in cAMP levels or P/Q-channel activity. However, it is mimicked and occluded by inhibition of L-type channels. Thus, interruption of the positive feedback between L-type Ca2+ channel activity and alpha1D gene expression can account for the long-lasting regulation of L-current produced by chronic activation of D2 dopamine receptors.
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9
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Fass DM, Takimoto K, Mains RE, Levitan ES. Tonic dopamine inhibition of L-type Ca2+ channel activity reduces alpha1D Ca2+ channel gene expression. J Neurosci 1999; 19:3345-52. [PMID: 10212294 PMCID: PMC6782228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/1998] [Revised: 02/11/1999] [Accepted: 02/12/1999] [Indexed: 02/12/2023] Open
Abstract
Hormones and neurotransmitters have both short-term and long-term modulatory effects on the activity of voltage-gated Ca2+ channels. Although much is known about the signal transduction underlying short-term modulation, there is far less information on mechanisms that produce long-term effects. Here, the molecular basis of long-lasting suppression of Ca2+ channel current in pituitary melanotropes by chronic dopamine exposure is examined. Experiments involving in vivo and in vitro treatments with the dopaminergic drugs haloperidol, bromocriptine, and quinpirole show that D2 receptors persistently decrease alpha1D L-type Ca2+ channel mRNA and L-type Ca2+ channel current without altering channel gating properties. In contrast, another L-channel (alpha1C) mRNA and P/Q-channel (alpha1A) mRNA are unaffected. The downregulation of alpha1D mRNA does not require decreases in cAMP levels or P/Q-channel activity. However, it is mimicked and occluded by inhibition of L-type channels. Thus, interruption of the positive feedback between L-type Ca2+ channel activity and alpha1D gene expression can account for the long-lasting regulation of L-current produced by chronic activation of D2 dopamine receptors.
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Affiliation(s)
- D M Fass
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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10
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Nikonorov IM, Blanck TJ, Recio-Pinto E. The effects of halothane on single human neuronal L-type calcium channels. Anesth Analg 1998; 86:885-95. [PMID: 9539620 DOI: 10.1097/00000539-199804000-00038] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
UNLABELLED We investigated halothane's effects on the function of L-type Ca2+ channels in a human neuronal cell line, SH-SY5Y, by using the cell-attached patch voltage clamp configuration and Ba2+ as the charge carrier. In multiple-channel patches, halothane decreased the peak and persistent Ba2+ currents, accelerated the rate of inactivation, and slowed the rate of activation. Single-channel analysis showed that halothane (0.14-1.26 mM) increased the latency time for the first channel opening, increased the lifetime of nonconducting events, increased the proportion of short-lived open events, decreased the lifetime of the two open populations, and increased the percentage of current traces without channel activity. All of the observed halothane effects contribute to the halothane-induced decrease in macroscopic Ba2+ currents. The halothane concentration producing 50% reduction (IC50) of the peak Ba2+ current was 0.80 mM (approximately 1.9 hypothetical minimum alveolar anesthetic concentration [H-MAC] at 28 degrees C) and of the persistent Ba2+ current was 0.69 mM (approximately 1.7 H-MAC). The halothane effects did not always occur together, and the Hill slope of 1.6 suggested the presence of more than one interaction site or of more than one population of L-type Ca2+ channels. Halothane reduces L-type Ca2+ channel currents in human neuronal cells primarily through the stabilization of nonconducting states such as closed (before and after channel opening) and inactivated states. IMPLICATIONS Calcium is a signaling molecule in neurons. We measured the effect of halothane on Ba2+ (a Ca2+ surrogate) movement into a human neuron-like cell electronically. Ba2+ entry through the L-type channel was depressed. Halothane decreased the likelihood of the channel opening and enhanced the rate at which the channel closed and inactivated. These actions of halothane are probably related to its anesthetic action.
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Affiliation(s)
- I M Nikonorov
- Department of Anesthesiology, The Hospital for Special Surgery, New York, New York 10021, USA
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Nikonorov IM, Blanck TJJ, Recio-Pinto E. The Effects of Halothane on Single Human Neuronal L-Type Calcium Channels. Anesth Analg 1998. [DOI: 10.1213/00000539-199804000-00038] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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12
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Gómez AM, Valdivia HH, Cheng H, Lederer MR, Santana LF, Cannell MB, McCune SA, Altschuld RA, Lederer WJ. Defective excitation-contraction coupling in experimental cardiac hypertrophy and heart failure. Science 1997; 276:800-6. [PMID: 9115206 DOI: 10.1126/science.276.5313.800] [Citation(s) in RCA: 546] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Cardiac hypertrophy and heart failure caused by high blood pressure were studied in single myocytes taken from hypertensive rats (Dahl SS/Jr) and SH-HF rats in heart failure. Confocal microscopy and patch-clamp methods were used to examine excitation-contraction (EC) coupling, and the relation between the plasma membrane calcium current (ICa) and evoked calcium release from the sarcoplasmic reticulum (SR), which was visualized as "calcium sparks." The ability of ICa to trigger calcium release from the SR in both hypertrophied and failing hearts was reduced. Because ICa density and SR calcium-release channels were normal, the defect appears to reside in a change in the relation between SR calcium-release channels and sarcolemmal calcium channels. beta-Adrenergic stimulation largely overcame the defect in hypertrophic but not failing heart cells. Thus, the same defect in EC coupling that develops during hypertrophy may contribute to heart failure when compensatory mechanisms fail.
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Affiliation(s)
- A M Gómez
- Department of Physiology and the Medical Biotechnology Center, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA. Universit
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Fass DM, Levitan ES. L-type Ca2+ channels access multiple open states to produce two components of Bay K 8644-dependent current in GH3 cells. J Gen Physiol 1996; 108:13-26. [PMID: 8817381 PMCID: PMC2229299 DOI: 10.1085/jgp.108.1.13] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
To determine the number of L-channel populations responsible for producing the two components of whole-cell L-type Ca2+ channel current revealed by Bay K 8644 (Fass, D.M., and E.S. Levitan. 1996. J. Gen. Physiol. 108:1-11), L-type Ca2+ channel activity was recorded in cell-attached patches. Ensemble tail currents from most (six out of nine) single-channel patches had double-exponential time courses, with time constants that were similar to whole-cell tail current decay values. Also, in single-channel patches subjected to two different levels of depolarization, ensemble tail currents exactly reproduced the voltage dependence of activation of the two whole-cell components: The slow component is activated at more negative potentials than the fast component. In addition, deactivation of Bay K 8644-modified whole-cell L-current was slower after long (100-ms) depolarizations than after short (20-ms) depolarizations, and this phenomenon was also evident in ensemble tail currents from single L-channels. Thus, a single population of L-channels can produce the two components of macroscopic L-current deactivation. To determine how individual L-channels produce multiple macroscopic tail current components, we constructed ensemble tail currents from traces that contained a single opening upon repolarization and no reopenings. These ensemble tails were biexponential. This type of analysis also revealed that reopenings do not contribute to the slowing of tail current deactivation after long depolarizations. Thus, individual L-channels must have access to several open states to produce multiple macroscopic current components. We also obtained evidence that access to these open states can vary over time. Use of several open states may give L-channels the flexibility to participate in many cell functions.
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Affiliation(s)
- D M Fass
- Department of Neuroscience, University of Pittsburgh, Pennsylvania 15261, USA
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