1
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Regulation of aldosterone production by ion channels: From basal secretion to primary aldosteronism. Biochim Biophys Acta Mol Basis Dis 2018; 1864:871-881. [DOI: 10.1016/j.bbadis.2017.12.034] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2017] [Revised: 12/05/2017] [Accepted: 12/23/2017] [Indexed: 01/07/2023]
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2
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Scholl UI, Stölting G, Nelson-Williams C, Vichot AA, Choi M, Loring E, Prasad ML, Goh G, Carling T, Juhlin CC, Quack I, Rump LC, Thiel A, Lande M, Frazier BG, Rasoulpour M, Bowlin DL, Sethna CB, Trachtman H, Fahlke C, Lifton RP. Recurrent gain of function mutation in calcium channel CACNA1H causes early-onset hypertension with primary aldosteronism. eLife 2015; 4:e06315. [PMID: 25907736 PMCID: PMC4408447 DOI: 10.7554/elife.06315] [Citation(s) in RCA: 221] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 03/25/2015] [Indexed: 01/05/2023] Open
Abstract
Many Mendelian traits are likely unrecognized owing to absence of traditional segregation patterns in families due to causation by de novo mutations, incomplete penetrance, and/or variable expressivity. Genome-level sequencing can overcome these complications. Extreme childhood phenotypes are promising candidates for new Mendelian traits. One example is early onset hypertension, a rare form of a global cause of morbidity and mortality. We performed exome sequencing of 40 unrelated subjects with hypertension due to primary aldosteronism by age 10. Five subjects (12.5%) shared the identical, previously unidentified, heterozygous CACNA1HM1549V mutation. Two mutations were demonstrated to be de novo events, and all mutations occurred independently. CACNA1H encodes a voltage-gated calcium channel (CaV3.2) expressed in adrenal glomerulosa. CACNA1HM1549V showed drastically impaired channel inactivation and activation at more hyperpolarized potentials, producing increased intracellular Ca2+, the signal for aldosterone production. This mutation explains disease pathogenesis and provides new insight into mechanisms mediating aldosterone production and hypertension. DOI:http://dx.doi.org/10.7554/eLife.06315.001 The consequence of mutations to the large majority of human genes is unknown. Most mutations that are currently known were discovered by tracing their effects through families. This allows the locations of mutations to be pinpointed on chromosomes—the structures that genetic material is packaged into. Other mutations are harder to trace because individuals with these mutations may develop very different signs and symptoms, or not develop clinical abnormalities at all. Alternatively, a trait may appear sporadically in a family because the mutation arises anew in the affected subject. Recently developed technologies that allow scientists to rapidly sequence all the gene-encoding regions of an individual's DNA—their genome—offer a new way to identify harmful genetic variants. Comparing the genomes of individuals with rare disorders can reveal if the individuals share any genetic mutations in common that could cause their symptoms. Scholl et al. used this strategy to sequence the genomes of 40 individuals with a rare type of hypertension—a condition that causes high blood pressure, and increases the risk of strokes, kidney failure and heart attacks—that develops early in childhood. In this form of the disease, high blood pressure is caused by the adrenal glands above the kidneys producing too much of a hormone called aldosterone. Some genetic causes of this form of the disease have already been identified. Now, Scholl et al. have found a new genetic mutation present in five families with this condition. Two of the individuals were the first in their families to develop this mutation, while three others inherited it. Some of the family members with this mutation had hypertension and some did not. The mutation is in a gene that encodes a type of calcium channel—a protein found in the membrane that surrounds cells, and which can open and close to control the amount of calcium in the cell. This particular calcium channel is abundant in the cells of the adrenal gland. Scholl et al. found that the mutation causes the calcium channels to be more likely to open and take longer to close. This increases the number of calcium ions that move into the cell, which causes the adrenal gland to produce more aldosterone. These new insights have provided a new way of diagnosing early-onset hypertension, and suggest that targeting calcium channels could help to develop new treatments for this disease. DOI:http://dx.doi.org/10.7554/eLife.06315.002
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Affiliation(s)
- Ute I Scholl
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
| | - Gabriel Stölting
- Institute of Complex Systems, Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany
| | - Carol Nelson-Williams
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
| | - Alfred A Vichot
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
| | - Murim Choi
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
| | - Erin Loring
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
| | - Manju L Prasad
- Department of Pathology, Yale University School of Medicine, New Haven, United States
| | - Gerald Goh
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
| | - Tobias Carling
- Yale Endocrine Neoplasia Laboratory, Yale School of Medicine, New Haven, United States
| | - C Christofer Juhlin
- Yale Endocrine Neoplasia Laboratory, Yale School of Medicine, New Haven, United States
| | - Ivo Quack
- Division of Nephrology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Lars C Rump
- Division of Nephrology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Anne Thiel
- Division of Nephrology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Marc Lande
- Division of Pediatric Nephrology, University of Rochester Medical Center, Rochester, United States
| | | | | | | | - Christine B Sethna
- Department of Pediatrics, Cohen Children's Medical Center of New York, New Hyde Park, United States
| | - Howard Trachtman
- Department of Pediatrics, NYU Langone Medical Center, New York, United States
| | - Christoph Fahlke
- Institute of Complex Systems, Zelluläre Biophysik, Forschungszentrum Jülich, Jülich, Germany
| | - Richard P Lifton
- Department of Genetics, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, United States
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3
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Ranzato E, Martinotti S, Magnelli V, Murer B, Biffo S, Mutti L, Burlando B. Epigallocatechin-3-gallate induces mesothelioma cell death via H2 O2 -dependent T-type Ca2+ channel opening. J Cell Mol Med 2014; 16:2667-78. [PMID: 22564432 PMCID: PMC4118235 DOI: 10.1111/j.1582-4934.2012.01584.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Malignant mesothelioma (MMe) is a highly aggressive, lethal tumour requiring the development of more effective therapies. The green tea polyphenol epigallocathechin-3-gallate (EGCG) inhibits the growth of many types of cancer cells. We found that EGCG is selectively cytotoxic to MMe cells with respect to normal mesothelial cells. MMe cell viability was inhibited by predominant induction of apoptosis at lower doses and necrosis at higher doses. EGCG elicited H2O2 release in cell cultures, and exogenous catalase (CAT) abrogated EGCG-induced cytotoxicity, apoptosis and necrosis. Confocal imaging of fluo 3-loaded, EGCG-exposed MMe cells showed significant [Ca2+]i rise, prevented by CAT, dithiothreitol or the T-type Ca2+ channel blockers mibefradil and NiCl2. Cell loading with dihydrorhodamine 123 revealed EGCG-induced ROS production, prevented by CAT, mibefradil or the Ca2+ chelator BAPTA-AM. Direct exposure of cells to H2O2 produced similar effects on Ca2+ and ROS, and these effects were prevented by the same inhibitors. Sensitivity of REN cells to EGCG was correlated with higher expression of Cav3.2 T-type Ca2+ channels in these cells, compared to normal mesothelium. Also, Cav3.2 siRNA on MMe cells reduced in vitro EGCG cytotoxicity and abated apoptosis and necrosis. Intriguingly, Cav3.2 expression was observed in malignant pleural mesothelioma biopsies from patients, but not in normal pleura. In conclusion, data showed the expression of T-type Ca2+ channels in MMe tissue and their role in EGCG selective cytotoxicity to MMe cells, suggesting the possible use of these channels as a novel MMe pharmacological target.
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Affiliation(s)
- Elia Ranzato
- Dipartimento di Scienze e Innovazione Tecnologica, DiSIT, University of Piemonte Orientale "Amedeo Avogadro", Alessandria, Italy.
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4
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Hong DH, Yang D, Choi IW, Son YK, Jung WK, Kim DJ, Han J, Na SH, Park WS. The T-type Ca2+ Channel Inhibitor Mibefradil Inhibits Voltage-Dependent K+ Channels in Rabbit Coronary Arterial Smooth Muscle Cells. J Pharmacol Sci 2012; 120:196-205. [DOI: 10.1254/jphs.12104fp] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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5
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Yan X, Gao S, Tang M, Xi J, Gao L, Zhu M, Luo H, Hu X, Zheng Y, Hescheler J, Liang H. Adenylyl cyclase/cAMP-PKA-mediated phosphorylation of basal L-type Ca(2+) channels in mouse embryonic ventricular myocytes. Cell Calcium 2011; 50:433-43. [PMID: 21824653 DOI: 10.1016/j.ceca.2011.07.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2011] [Revised: 06/16/2011] [Accepted: 07/12/2011] [Indexed: 10/17/2022]
Abstract
In fetal mammalian heart, constitutive adenylyl cyclase/cyclic AMP-dependent protein kinase A (cAMP-PKA)-mediated phosphorylation, independent of β-adrenergic receptor stimulation, could under such circumstances play an important role in sustaining the L-type calcium channel current (I(Ca,L)) and regulating other PKA dependent phosphorylation targets. In this study, we investigated the regulation of L-type Ca(2+) channel (LTCC) in murine embryonic ventricles. The data indicated a higher phosphorylation state of LTCC at early developmental stage (EDS, E9.5-E11.5) than late developmental stage (LDS, E16.5-E18.5). An intrinsic adenylyl cyclase (AC) activity, PKA activity and basal cAMP concentration were obviously higher at EDS than LDS. The cAMP increase in the presence of isobutylmethylxanthine (IBMX, nonselective phosphodiesterase inhibitor) was further augmented at LDS but not at EDS by chelation of intracellular Ca(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester (BAPTA-AM). Furthermore, I(Ca,L) increased with time after patch rupture in LDS cardiomyocytes dialyzed with pipette solution containing BAPTA whereas not at EDS. Thus we conclude that the high basal level of LTCC phosphorylation is due to the high intrinsic PKA activity and the high intrinsic AC activity at EDS. The latter is possibly owing to the little or no effect of Ca(2+) influx via LTCCs on AC activity, leading to the inability to inhibit AC.
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Affiliation(s)
- Xisheng Yan
- Department of Physiology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
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6
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Bartels P, Behnke K, Michels G, Groner F, Schneider T, Henry M, Barrett PQ, Kang HW, Lee JH, Wiesen MHJ, Matthes J, Herzig S. Structural and biophysical determinants of single Ca(V)3.1 and Ca(V)3.2 T-type calcium channel inhibition by N(2)O. Cell Calcium 2009; 46:293-302. [PMID: 19783046 DOI: 10.1016/j.ceca.2009.09.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2009] [Revised: 09/02/2009] [Accepted: 09/04/2009] [Indexed: 10/20/2022]
Abstract
We investigated the biophysical mechanism of inhibition of recombinant T-type calcium channels Ca(V)3.1 and Ca(V)3.2 by nitrous oxide (N(2)O). To identify functionally important channel structures, chimeras with reciprocal exchange of the N-terminal domains I and II and C-terminal domains III and IV were examined. In whole-cell recordings N(2)O significantly inhibited Ca(V)3.2, and - less pronounced - Ca(V)3.1. A Ca(V)3.2-prevalent inhibition of peak currents was also detected in cell-attached multi-channel patches. In cell-attached patches containing < or = 3 channels N(2)O reduced average peak current of Ca(V)3.2 by decreasing open probability and open time duration. Effects on Ca(V)3.1 were smaller and mediated by a reduced fraction of sweeps containing channel activity. Without drug, single Ca(V)3.1 channels were significantly less active than Ca(V)3.2. Chimeras revealed that domains III and IV control basal gating properties. Domains I and II, in particular a histidine residue within Ca(V)3.2 (H191), are responsible for the subtype-prevalent N(2)O inhibition. Our study demonstrates the biophysical (open times, open probability) and structural (domains I and II) basis of action of N(2)O on Ca(V)3.2. Such a fingerprint of single channels can help identifying the molecular nature of native channels. This is exemplified by a characterization of single channels expressed in human hMTC cells as functional homologues of recombinant Ca(V)3.1.
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Affiliation(s)
- Peter Bartels
- Department of Pharmacology, University of Cologne, 50931 Koeln, Germany
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7
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Michels G, Khan IF, Endres-Becker J, Rottlaender D, Herzig S, Ruhparwar A, Wahlers T, Hoppe UC. Regulation of the Human Cardiac Mitochondrial Ca
2+
Uptake by 2 Different Voltage-Gated Ca
2+
Channels. Circulation 2009; 119:2435-43. [DOI: 10.1161/circulationaha.108.835389] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Background—
Impairment of intracellular Ca
2+
homeostasis and mitochondrial function has been implicated in the development of cardiomyopathy. Mitochondrial Ca
2+
uptake is thought to be mediated by the Ca
2+
uniporter (MCU) and a thus far speculative non-MCU pathway. However, the identity and properties of these pathways are a matter of intense debate, and possible functional alterations in diseased states have remained elusive.
Methods and Results—
By patch clamping the inner membrane of mitochondria from nonfailing and failing human hearts, we have identified 2 previously unknown Ca
2+
-selective channels, referred to as mCa1 and mCa2. Both channels are voltage dependent but differ significantly in gating parameters. Compared with mCa2 channels, mCa1 channels exhibit a higher single-channel amplitude, shorter openings, a lower open probability, and 3 to 5 subconductance states. Similar to the MCU, mCa1 is inhibited by 200 nmol/L ruthenium 360, whereas mCa2 is insensitive to 200 nmol/L ruthenium 360 and reduced only by very high concentrations (10 μmol/L). Both mitochondrial Ca
2+
channels are unaffected by blockers of other possibly Ca
2+
-conducting mitochondrial pores but were activated by spermine (1 mmol/L). Notably, activity of mCa1 and mCa2 channels is decreased in failing compared with nonfailing heart conditions, making them less effective for Ca
2+
uptake and likely Ca
2+
-induced metabolism.
Conclusions—
Thus, we conclude that the human mitochondrial Ca
2+
uptake is mediated by these 2 distinct Ca
2+
channels, which are functionally impaired in heart failure. Current properties reveal that the mCa1 channel underlies the human MCU and that the mCa2 channel is responsible for the ruthenium red–insensitive/low-sensitivity non-MCU–type mitochondrial Ca
2+
uptake.
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Affiliation(s)
- Guido Michels
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Ismail F. Khan
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Jeannette Endres-Becker
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Dennis Rottlaender
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Stefan Herzig
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Arjang Ruhparwar
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Thorsten Wahlers
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
| | - Uta C. Hoppe
- From the Department of Internal Medicine III (G.M., I.F.K., J.E.-B., D.R., U.C.H.), Center for Molecular Medicine (S.H., U.C.H.), Institute of Pharmacology (S.H.), and Department of Cardiothoracic Surgery (T.W.), University of Cologne, Cologne, and Department of Cardiac Surgery, University of Heidelberg, Heidelberg (A.R.), Germany
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8
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Perez-Reyes E, Van Deusen AL, Vitko I. Molecular pharmacology of human Cav3.2 T-type Ca2+ channels: block by antihypertensives, antiarrhythmics, and their analogs. J Pharmacol Exp Ther 2008; 328:621-7. [PMID: 18974361 DOI: 10.1124/jpet.108.145672] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Antihypertensive drugs of the "calcium channel blocker" or "calcium antagonist" class have been used to establish the physiological role of L-type Ca(2+) channels in vascular smooth muscle. In contrast, there has been limited progress on the pharmacology T-type Ca(2+) channels. T-type channels play a role in cardiac pacemaking, aldosterone secretion, and renal hemodynamics, leading to the hypothesis that mixed T- and L-type blockers may have therapeutic advantages over selective L-type blockers. The goal of this study was to identify compounds that block the Ca(v)3.2 T-type channel with high affinity, focusing on two classes of compounds: phenylalkylamines (e.g., mibefradil) and dihydropyridines (e.g., efonidipine). Compounds were tested using a validated Ca(2+) influx assay into a cell line expressing recombinant Ca(v)3.2 channels. This study identified four clinically approved antihypertensive drugs (efonidipine, felodipine, isradipine, and nitrendipine) as potent T-channel blockers (IC(50) < 3 microM). In contrast, other widely prescribed dihydropyridines, such as amlodipine and nifedipine, were 10-fold less potent, making them a more appropriate choice in research studies on the role of L-type currents. In summary, the present results support the notion that many available antihypertensive drugs block a substantial fraction of T-current at therapeutically relevant concentrations, contributing to their mechanism of action.
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Affiliation(s)
- Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia, USA.
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9
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Lin Z, Witschas K, Garcia T, Chen RS, Hansen JP, Sellers ZM, Kuzmenkina E, Herzig S, Best PM. A critical GxxxA motif in the gamma6 calcium channel subunit mediates its inhibitory effect on Cav3.1 calcium current. J Physiol 2008; 586:5349-66. [PMID: 18818244 DOI: 10.1113/jphysiol.2008.159111] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The eight members of the calcium channel gamma subunit family are integral membrane proteins that regulate the expression and behaviour of voltage and ligand gated ion channels. While a subgroup consisting of gamma(2), gamma(3), gamma(4) and gamma(8) (the TARPs) modulate AMPA receptor localization and function, the gamma(1) and gamma(6) subunits conform to the original description of these proteins as regulators of voltage gated calcium channels. We have previously shown that the gamma(6) subunit is highly expressed in atrial myocytes and that it is capable of acting as a negative modulator of low voltage activated calcium current. In this study we extend our understanding of gamma(6) subunit modulation of low voltage activated calcium current. Using engineered chimeric constructs, we demonstrate that the first transmembrane domain (TM1) of gamma(6) is necessary for its inhibitory effect on Cav3.1 current. Mutational analysis is then used to identify a unique GxxxA motif within TM1 that is required for the function of the subunit strongly suggesting the involvement of helix-helix interactions in its effects. Results from co-immunoprecipitation experiments confirm a physical association of gamma(6) with the Cav3.1 channel in both HEK cells and atrial myocytes. Single channel analysis reveals that binding of gamma(6) reduces channel availability for activation. Taken together, the results of this study provide both a molecular and a mechanistic framework for understanding the unique ability of the gamma(6) calcium channel subunit to modulate low voltage activated (Cav3.1) calcium current density.
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Affiliation(s)
- Zuojun Lin
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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10
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Michels G, Er F, Khan IF, Endres-Becker J, Brandt MC, Gassanov N, Johns DC, Hoppe UC. K+ channel regulator KCR1 suppresses heart rhythm by modulating the pacemaker current If. PLoS One 2008; 3:e1511. [PMID: 18231597 PMCID: PMC2204056 DOI: 10.1371/journal.pone.0001511] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2007] [Accepted: 12/22/2007] [Indexed: 01/20/2023] Open
Abstract
Hyperpolarization-activated, cyclic nucleotide sensitive (HCN) channels underlie the pacemaker current I(f), which plays an essential role in spontaneous cardiac activity. HCN channel subunits (HCN1-4) are believed to be modulated by additional regulatory proteins, which still have to be identified. Using biochemistry, molecularbiology and electrophysiology methods we demonstrate a protein-protein interaction between HCN2 and the K(+) channel regulator protein 1, named KCR1. In coimmunoprecipitation experiments we show that KCR1 and HCN2 proteins are able to associate. Heterologously expressed HCN2 whole-cell current density was significantly decreased by KCR1. KCR1 profoundly suppressed I(HCN2) single-channel activity, indicating a functional interaction between KCR1 and the HCN2 channel subunit. Endogenous KCR1 expression could be detected in adult and neonatal rat ventriculocytes. Adenoviral-mediated overexpression of KCR1 in rat cardiomyocytes (i) reduced I(f) whole-cell currents, (ii) suppressed most single-channel gating parameters, (iii) altered the activation kinetics, (iv) suppressed spontaneous action potential activity, and (v) the beating rate. More importantly, siRNA-based knock-down of endogenous KCR1 increased the native I(f) current size and single-channel activity and accelerated spontaneous beating rate, supporting an inhibitory action of endogenous KCR1 on native I(f). Our observations demonstrate for the first time that KCR1 modulates I(HCN2)/I(f) channel gating and indicate that KCR1 serves as a regulator of cardiac automaticity.
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Affiliation(s)
- Guido Michels
- Department of Internal Medicine III, University of Cologne, Cologne, Germany
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11
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Herzig S, Khan IFY, Gründemann D, Matthes J, Ludwig A, Michels G, Hoppe UC, Chaudhuri D, Schwartz A, Yue DT, Hullin R. Mechanism of Ca(v)1.2 channel modulation by the amino terminus of cardiac beta2-subunits. FASEB J 2007; 21:1527-38. [PMID: 17289923 DOI: 10.1096/fj.06-7377com] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
L-type calcium channels are composed of a pore, alpha1c (Ca(V)1.2), and accessory beta- and alpha2delta-subunits. The beta-subunit core structure was recently resolved at high resolution, providing important information on many functional aspects of channel modulation. In this study we reveal differential novel effects of five beta2-subunits isoforms expressed in human heart (beta(2a-e)) on the single L-type calcium channel current. These splice variants differ only by amino-terminal length and amino acid composition. Single-channel modulation by beta2-subunit isoforms was investigated in HEK293 cells expressing the recombinant L-type ion conducting pore. All beta2-subunits increased open probability, availability, and peak current with a highly consistent rank order (beta2a approximately = beta2b > beta2e approximately = beta2c > beta2d). We show graded modulation of some transition rates within and between deep-closed and inactivated states. The extent of modulation correlates strongly with the length of amino-terminal domains. Two mutant beta2-subunits that imitate the natural span related to length confirm this conclusion. The data show that the length of amino termini is a relevant physiological mechanism for channel closure and inactivation, and that natural alternative splicing exploits this principle for modulation of the gating properties of calcium channels.
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Affiliation(s)
- Stefan Herzig
- Department of Pharmacology, University of Cologne, Gleueler Strasse 24, 50931 Köln, Germany.
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12
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Gautam SH, Otsuguro KI, Ito S, Saito T, Habara Y. T-type Ca2+ channels mediate propagation of odor-induced Ca2+ transients in rat olfactory receptor neurons. Neuroscience 2006; 144:702-13. [PMID: 17110049 DOI: 10.1016/j.neuroscience.2006.10.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2006] [Revised: 10/07/2006] [Accepted: 10/09/2006] [Indexed: 11/26/2022]
Abstract
Propagation of odor-induced Ca(2+) transients from the cilia/knob to the soma in mammalian olfactory receptor neurons (ORNs) is thought to be mediated exclusively by high-voltage-activated Ca(2+) channels. However, using confocal Ca(2+) imaging and immunocytochemistry we identified functional T-type Ca(2+) channels in rat ORNs. Here we show that T-type Ca(2+) channels in ORNs also mediate propagation of odor-induced Ca(2+) transients from the knob to the soma. In the presence of the selective inhibitor of T-type Ca(2+) channels mibefradil (10-15 microM) or Ni(2+) (100 microM), odor- and forskolin/3-isobutyl-1-methyl-xanthine (IBMX)-induced Ca(2+) transients in the soma and dendrite were either strongly inhibited or abolished. The percentage of inhibition of the Ca(2+) transients in the knob, however, was 40-50% less than that in the soma. Ca(2+) transients induced by 30 mM K(+) were partially inhibited by mibefradil, but without a significant difference in the extent of inhibition between the knob and soma. Furthermore, an increase of as little as 2.5 mM in the extracellular K(+) concentration (7.5 mM K(+)) was found to induce Ca(2+) transients in ORNs, and such responses were completely inhibited by mibefradil or Ni(2+). Total replacement of extracellular Na(+) with N-methyl-d-glutamate inhibited none of the odor-, forskolin/IBMX- or 7.5 mM K(+)-induced Ca(2+) transients. Positive immunoreactivity to the Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3 subunits of the T-type Ca(2+) channel was observed throughout the soma, dendrite and knob. These data suggest that involvement of T-type Ca(2+) channels in the propagation of odor-induced Ca(2+) transients in ORNs may contribute to signal transduction and odor sensitivity.
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Affiliation(s)
- S H Gautam
- Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
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13
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Michels G, Er F, Eicks M, Herzig S, Hoppe UC. Long-term and immediate effect of testosterone on single T-type calcium channel in neonatal rat cardiomyocytes. Endocrinology 2006; 147:5160-9. [PMID: 16873532 DOI: 10.1210/en.2006-0186] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In the cardiovascular system, T-type calcium channels play an important role for the intracellular calcium homeostasis and spontaneous pacemaker activity and are involved in the progression of structural heart diseases. Androgens influence the cardiovascular physiology and pathophysiology. However, their effect on native T-type calcium currents (I(Ca,T)) remains unclear. To test the chronic effect of testosterone on the cardiac I(Ca,T), cultured neonatal rat ventricular cardiomyocytes were treated with testosterone (1 nM-10 microM) for 24-30 h. Current measurements were performed after testosterone washout to exclude any acute testosterone effects. Testosterone (100 nm) pretreatment significantly increased whole-cell I(Ca,T) density from 1.26 +/- 0.48 pA/pF (n = 8) to 5.06 +/- 1.75 pA/pF (n = 7; P < 0.05) and accelerated beating rate. This was attributed to both increased expression levels of the pore-forming subunits Ca(v)3.1 and Ca(v)3.2 and increased T-type single-channel activity. On single-channel level, the increase of the ensemble average current by testosterone vs. time-matched controls was due to an increased availability (58.1 +/- 4.2 vs. 21.5 +/- 4.0%, P < 0.01) and open probability (2.78 +/- 0.29 vs. 0.85 +/- 0.23%, P < 0.01). Cotreatment with the selective testosterone receptor antagonist flutamide (10 mum) prevented these chronic testosterone-induced effects. Conversely, acute application of testosterone (10 microM) decreased T-type single-channel activity in testosterone pretreated cells by reducing the open probability (0.78 +/- 0.13 vs. 2.91 +/- 0.38%, P < 0.01), availability (23.6 +/- 3.3 vs. 57.6 +/- 4.5%, P < 0.01), and peak current (-20 +/- 4 vs. -58 +/- 4 fA, P < 0.01). Flutamide (10 microM) did not abolish the testosterone-induced acute block of T-type calcium channels. Our results indicate that long-term testosterone treatment increases, whereas acute testosterone decreases neonatal rat T-type calcium currents. These effects seem to be mediated by a genomic chronic stimulation and a nongenomic acute inhibitory action.
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Affiliation(s)
- Guido Michels
- Department of Internal Medicine III, University of Cologne, Kerpener Strasse 62, 50937 Cologne, Germany
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14
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Gautam SH, Otsuguro KI, Ito S, Saito T, Habara Y. T-type Ca2+ channels contribute to IBMX/forskolin- and K(+)-induced Ca(2+) transients in porcine olfactory receptor neurons. Neurosci Res 2006; 57:129-39. [PMID: 17074407 DOI: 10.1016/j.neures.2006.09.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 09/15/2006] [Accepted: 09/25/2006] [Indexed: 01/08/2023]
Abstract
T-type Ca(2+) channels are low-voltage-activated Ca(2+) channels that control Ca(2+) entry in excitable cells during small depolarization above resting potentials. Using Ca(2+) imaging with a laser scanning confocal microscope we investigated the involvement of T-type Ca(2+) channels in IBMX/forskolin- and sparingly elevated extracellular K(+)-induced Ca(2+) transients in freshly isolated porcine olfactory receptor neurons (ORNs). In the presence of mibefradil (10microM) or Ni(2+) (100microM), the selective T-type Ca(2+) channel inhibitors, IBMX/forskolin-induced Ca(2+) transients in the soma were either strongly (>60%) inhibited or abolished completely. However, the Ca(2+) transients in the knob were only partially (<60%) inhibited. Ca(2+) transients induced by 30mM K(+) were also partially ( approximately 60%) inhibited at both the knob and soma. Furthermore, ORNs responded to as little as a 2.5mM increase in the extracellular K(+) concentration (7.5mM K(+)), and such responses were completely inhibited by mibefradil or Ni(2+). These results reveal functional expression of T-type Ca(2+) channels in porcine ORNs, and suggest a role for these channels in the spread Ca(2+) transients from the knob to the soma during activation of the cAMP cascade following odorant binding to G-protein-coupled receptors on the cilia/knob of ORNs.
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Affiliation(s)
- Shree Hari Gautam
- Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
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15
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Emerick MC, Stein R, Kunze R, McNulty MM, Regan MR, Hanck DA, Agnew WS. Profiling the array of Ca(v)3.1 variants from the human T-type calcium channel gene CACNA1G: alternative structures, developmental expression, and biophysical variations. Proteins 2006; 64:320-42. [PMID: 16671074 DOI: 10.1002/prot.20877] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We describe the regulated transcriptome of CACNA1G, a human gene for T-type Ca(v)3.1 calcium channels that is subject to extensive alternative RNA splicing. Fifteen sites of transcript variation include 2 alternative 5'-UTR promoter sites, 2 alternative 3'-UTR polyadenylation sites, and 11 sites of alternative splicing within the open reading frame. A survey of 1580 fetal and adult human brain full-length complementary DNAs reveals a family of 30 distinct transcripts, including multiple functional forms that vary in expression with development. Statistical analyses of fetal and adult transcript populations reveal patterns of linkages among intramolecular splice site configurations that change dramatically with development. A shift from nearly independent, biased splicing in fetal transcripts to strongly concerted splicing in adult transcripts suggests progressive activation of multiple "programs" of splicing regulation that reorganize molecular structures in differentiating cells. Patch-clamp studies of nine selected variants help relate splicing regulation to permutations of the gating parameters most likely to modify T-channel physiology in expressing neurons. Gating behavior reflects combinatorial interactions between variable domains so that molecular phenotype depends on ensembles of coselected domains, consistent with the observed emergence of concerted splicing during development. We conclude that the structural gene and networks of splicing regulatory factors define an integrated system for the phenotypic variation of Ca(v)3.1 biophysics during nervous system development.
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Affiliation(s)
- Mark C Emerick
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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16
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Michels G, Er F, Khan I, Südkamp M, Herzig S, Hoppe UC. Single-Channel Properties Support a Potential Contribution of Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels and
I
f
to Cardiac Arrhythmias. Circulation 2005; 111:399-404. [PMID: 15687126 DOI: 10.1161/01.cir.0000153799.65783.3a] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background—
The pacemaker current
I
f
is present in atrial and ventricular myocytes. However, it remains controversial whether
I
f
overexpression in diseased states might play a role for arrhythmogenesis, because first
I
f
activation in whole-cell recordings hardly overlapped the diastolic voltage of working myocardium.
Methods and Results—
To obtain further insight into
I
HCN
and
I
f
properties, we provide for the first time detailed single-channel analysis of heterologously expressed hyperpolarization-activated cyclic nucleotide-gated (HCN) isoforms and native human
I
f
. HCN subtypes differed significantly in single-channel amplitude, conductance, and activation kinetics. Interestingly, threshold potentials of HCN isoforms were more positive than would have been expected from whole-cell measurements. Single-channel properties of cells cotransfected with HCN2 and HCN4 were distinct from cells expressing HCN2 or HCN4 alone, demonstrating that different HCN isoforms can influence current properties of a single HCN channel complex, thus providing direct functional evidence for HCN heteromerization. Pooled data of homomeric and heteromeric HCN channels and of native
I
f
extrapolated from maximum likelihood fits indicated a multistate gating scheme comprising 5 closed- and 4 open-channel states. Single-channel characteristics of
I
f
in human atrial myocytes closely resembled those of HCN4 or HCN2+HCN4, supporting the hypothesis that native
I
f
channels in atrial myocardium are heteromeric complexes composed of HCN4 and/or HCN2. Most interestingly, half-maximal activation of single-channel atrial
I
f
(−68.3±4.9 mV; k=−9.9±1.5; n=8) was well within the diastolic voltage range of human atrial myocardium.
Conclusions—
These observations support a potential contribution of HCN/
I
f
to the arrhythmogenesis of working myocardium under pathological conditions.
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Affiliation(s)
- Guido Michels
- Department of Internal Medicine III, University of Cologne, Cologne, Germany
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17
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Abstract
Mibefradil is a T-type Ca2+ channel antagonist with reported cross-reactivity with other classes of ion channels, including K+, Cl-, and Na+ channels. Using whole-cell voltage clamp, we examined mibefradil block of four Na+ channel isoforms expressed in human embryonic kidney cells: Nav1.5 (cardiac), Nav1.4 (skeletal muscle), Nav1.2 (brain), and Nav1.7 (peripheral nerve). Mibefradil blocked Nav1.5 in a use/frequency-dependent manner, indicating preferential binding to states visited during depolarization. Mibefradil blocked currents of all Na+ channel isoforms with similar affinity and a dependence on holding potential, and drug off-rate was slowed at depolarized potentials (k(off) was 0.024/s at -130 mV and 0.007/s at -100 mV for Nav1.5). We further probed the interaction of mibefradil with inactivated Nav1.5 channels. Neither the degree nor the time course of block was dependent on the stimulus duration, which dramatically changed the residency time of channels in the fast-inactivated state. In addition, inhibiting the binding of the fast inactivation lid (Nav1.5 ICM + MTSET) did not alter mibefradil block, confirming that the drug does not preferentially interact with the fast-inactivated state. We also tested whether mibefradil interacted with slow-inactivated state(s). When selectively applied to channels after inducing slow inactivation with a 60-s pulse to -10 mV, mibefradil (1 microM) produced 45% fractional block in Nav1.5 and greater block (88%) in an isoform (Nav1.4) that slow-inactivates more completely. Our results suggest that mibefradil blocks Na+ channels in a state-dependent manner that does not depend on fast inactivation but probably involves interaction with one or more slow-inactivated state(s).
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Affiliation(s)
- Megan M McNulty
- Department of Neurobiology, University of Chicago, Illinois, USA
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18
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Brueggemann LI, Martin BL, Barakat J, Byron KL, Cribbs LL. Low voltage-activated calcium channels in vascular smooth muscle: T-type channels and AVP-stimulated calcium spiking. Am J Physiol Heart Circ Physiol 2004; 288:H923-35. [PMID: 15498818 DOI: 10.1152/ajpheart.01126.2003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An important path of extracellular calcium influx in vascular smooth muscle (VSM) cells is through voltage-activated Ca2+ channels of the plasma membrane. Both high (HVA)- and low (LVA)-voltage-activated Ca2+ currents are present in VSM cells, yet little is known about the relevance of the LVA T-type channels. In this report, we provide molecular evidence for T-type Ca2+ channels in rat arterial VSM and characterize endogenous LVA Ca2+ currents in the aortic smooth muscle-derived cell line A7r5. AVP is a vasoconstrictor hormone that, at physiological concentrations, stimulates Ca2+ oscillations (spiking) in monolayer cultures of A7r5 cells. The present study investigated the role of T-type Ca2+ channels in this response with a combination of pharmacological and molecular approaches. We demonstrate that AVP-stimulated Ca2+ spiking can be abolished by mibefradil at low concentrations (<1 microM) that should not inhibit L-type currents. Infection of A7r5 cells with an adenovirus containing the Cav3.2 T-type channel resulted in robust LVA Ca2+ currents but did not alter the AVP-stimulated Ca2+ spiking response. Together these data suggest that T-type Ca2+ channels are necessary for the onset of AVP-stimulated calcium oscillations; however, LVA Ca2+ entry through these channels is not limiting for repetitive Ca2+ spiking observed in A7r5 cells.
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Affiliation(s)
- Lioubov I Brueggemann
- Department of Medicine, Cardiovascular Institute, Loyola University Medical Center, Maywood, Illinois 60153, USA
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19
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Triggle DJ. Drug targets in the voltage-gated calcium channel family: why some are and some are not. Assay Drug Dev Technol 2004; 1:719-33. [PMID: 15090244 DOI: 10.1089/154065803770381075] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The L-type calcium channel antagonists have been, and continue to be, a very successful group of therapeutic agents targeted at cardiovascular disorders, notably angina and hypertension. The discovery that the voltage-gated calcium channels are a large and widely distributed family with important roles in both the peripheral and central nervous systems has initiated a major search for drugs active at other calcium channel types directed at disorders of the central nervous system, including pain, epilepsy, and stroke. These efforts have not been therapeutically successful thus far, and small molecule equivalents of the L-type blockers nifedipine, diltiazem, and verapamil directed at non-L-type channels have not been found. The underlying reasons for this are discussed together with suggestions for new directions, including fertility control, oxygen-sensitive channels, and calcium channel activators.
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Affiliation(s)
- David J Triggle
- School of Pharmacy and Pharmaceutical Sciences, SUNY at Buffalo, Buffalo, NY 14260, USA.
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20
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Foerster K, Kaeferstein T, Groner F, Engelhardt S, Matthes J, Koch WJ, Lohse MJ, Herzig S. Calcium channel function and regulation in beta 1- and beta 2-adrenoceptor transgenic mice. Naunyn Schmiedebergs Arch Pharmacol 2004; 369:490-5. [PMID: 15083268 DOI: 10.1007/s00210-004-0928-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2003] [Accepted: 03/22/2004] [Indexed: 12/13/2022]
Abstract
Cardiac effects of catecholamines on the L-type calcium channel depend on beta-adrenoceptor subtype (beta(1)- vs. beta(2)-adrenoceptor). Chronic overexpression of these receptors leads to hypertrophy and early death at moderate (beta(1)) or excessive (beta(2)) levels of overexpression respectively. In order to examine the role of L-type calcium channels in altered cardiomyocyte calcium homeostasis found with beta(1)-adrenoceptor overexpression, and to understand the quantitative differences between beta-adrenoceptor subtypes regarding calcium channel regulation, we examined single channels in myocytes obtained from beta(1)- and beta(2)-adrenoceptor transgenic mice. The effects of the agonist isoproterenol were investigated and compared with acute receptor stimulation in the respective non-transgenic littermates. Channels from beta(1)-adrenoceptor transgenic mice have normal baseline activity, and channel number is not reduced. This contrasts to previous findings with beta(2)-adrenoceptor transgenic mice, where channel activity is depressed. Isoproterenol is unable to stimulate channel activity in both transgenic models. In conclusion, the L-type calcium channel is not likely to be involved in alterations of calcium handling of beta(1)-adrenoceptor transgenic myocytes. Furthermore, chronic beta(1)-adrenoceptor overexpression does not depress channel activity, giving another example of the difference between beta(1)- and beta(2)-adrenoceptor signal transduction.
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MESH Headings
- Adrenergic beta-Agonists/pharmacology
- Animals
- Calcium Channel Blockers/metabolism
- Calcium Channels/drug effects
- Calcium Channels/physiology
- Isoproterenol/pharmacology
- Isradipine/metabolism
- Mice
- Mice, Transgenic
- Myocytes, Cardiac
- Receptors, Adrenergic, beta-1/drug effects
- Receptors, Adrenergic, beta-1/physiology
- Receptors, Adrenergic, beta-2/drug effects
- Receptors, Adrenergic, beta-2/physiology
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Affiliation(s)
- Katharina Foerster
- Department of Pharmacology, University of Cologne, Gleueler Strasse 24, 50931 Cologne, Germany
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21
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Groner F, Rubio M, Schulte-Euler P, Matthes J, Khan IFY, Bodi I, Koch SE, Schwartz A, Herzig S. Single-channel gating and regulation of human L-type calcium channels in cardiomyocytes of transgenic mice. Biochem Biophys Res Commun 2004; 314:878-84. [PMID: 14741718 DOI: 10.1016/j.bbrc.2003.12.174] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Overexpression of human cardiac L-type Ca(2+) channel pores (hCa(v)1.2) in mice causes heart failure. Earlier studies showed Ca(v)1.2-mRNA increase by 2.8-fold, but whole-cell current density enhancement by </=1.5-fold only. Three possible explanations were examined: (1) poor translation of hCa(v)1.2 and of its accessory subunits, (2) altered sarcolemmal insertion of functional channels, and (3) lower single-channel activity of overexpressed channels. Western blots revealed a 2.7-fold increase of Ca(v)1.2 protein in transgenic myocytes, but less enhanced expression of beta(1a) and beta(1b) subunits. beta(2) and alpha(2)/delta were significantly lowered. Density of functional channels was increased by 3.0-fold. Single-channel gating was impaired in transgenic cardiomyocytes: open probability and ensemble average currents were reduced by 60%. Furthermore, channels of transgenic myocytes were not stimulated by 8-Br-cAMP, in contrast to wild-types. Expression of malcomposed, dysfunctional L-type Ca(2+) channels in murine cardiomyocytes overexpressing hCa(v)1.2 explains the moderate enhancement of whole-cell currents and illustrates compensatory mechanisms in a transgenic disease model.
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Affiliation(s)
- Ferdi Groner
- Department of Pharmacology, University of Cologne, 50931, Köln, Germany
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22
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Foerster K, Groner F, Matthes J, Koch WJ, Birnbaumer L, Herzig S. Cardioprotection specific for the G protein Gi2 in chronic adrenergic signaling through beta 2-adrenoceptors. Proc Natl Acad Sci U S A 2003; 100:14475-80. [PMID: 14612574 PMCID: PMC283616 DOI: 10.1073/pnas.1936026100] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Two subtypes of beta-adrenoceptors, beta 1 and beta 2, mediate cardiac catecholamine effects. These two types differ qualitatively, e.g., regarding G protein coupling and calcium channel stimulation. Transgenic mice overexpressing human beta 2-adrenoceptors survive high-expression levels, unlike mice overexpressing beta 1-adrenoceptors. We examined the role of inhibitory Gi proteins, known to be activated by beta 2- but not beta 1-adrenoceptors, on the chronic effects of human beta 2-adrenoreceptor overexpression in transgenic mice. These mice were crossbred with mice where G alpha i2, a functionally important cardiac Gi alpha-subunit, was inactivated by targeted gene deletion. Survival of beta 2-adrenoreceptor transgenic mice was reduced by heterozygous inactivation of G alpha i2. Homozygous knockout/beta 2-adrenoreceptor transgenic mice died within 4 days after birth. Heterozygous knockout/beta 2-adrenoreceptor transgenic mice developed more pronounced cardiac hypertrophy and earlier heart failure compared with beta 2-adrenoreceptor transgenic mice. Single calcium-channel activity was strongly suppressed in heterozygous knockout/beta 2-adrenoreceptor transgenic mice. In cardiomyocytes from these mice, pertussis toxin treatment in vitro fully restored channel activity and enhanced channel activity in cells from homozygous G alpha i2 knockout animals. Cardiac G alpha i3 protein was increased in all G alpha i2 knockout mouse strains. Our results demonstrate that G alpha i2 takes an essential protective part in chronic signaling of overexpressed beta 2-adrenoceptors, leading to prolonged survival and delayed cardiac pathology. However, reduction of calcium-channel activity by beta 2-adrenoreceptor overexpression is due to a different pertussis-toxin-sensitive pathway, most likely by G alpha i3. This result indicates that subtype-specific signaling of beta 2-adrenoreceptor functionally bifurcates at the level of Gi, leading to different effects depending on the G alpha isoform.
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MESH Headings
- Animals
- Base Sequence
- Calcium Channels/metabolism
- DNA/genetics
- GTP-Binding Protein alpha Subunit, Gi2
- GTP-Binding Protein alpha Subunits, Gi-Go/deficiency
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Proteins/genetics
- GTP-Binding Proteins/metabolism
- Gene Expression
- Humans
- Ion Channel Gating/drug effects
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Mice, Transgenic
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Pertussis Toxin/toxicity
- Proto-Oncogene Proteins/deficiency
- Proto-Oncogene Proteins/genetics
- Proto-Oncogene Proteins/metabolism
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Signal Transduction
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Affiliation(s)
- Katharina Foerster
- Department of Pharmacology, University of Cologne, Gleueler Strasse 24, 50931 Cologne, Germany
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23
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Pinato G, Midtgaard J. Regulation of granule cell excitability by a low-threshold calcium spike in turtle olfactory bulb. J Neurophysiol 2003; 90:3341-51. [PMID: 12867531 DOI: 10.1152/jn.00560.2003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Granule cells excitability in the turtle olfactory bulb was analyzed using whole cell recordings in current- and voltage-clamp mode. Low-threshold spikes (LTSs) were evoked at potentials that are subthreshold for Na spikes in normal medium. The LTSs were evoked from rest, but hyperpolarization of the cell usually increased their amplitude so that they more easily boosted Na spike initiation. The LTS persisted in the presence of TTX but was antagonized by blockers of T-type calcium channels. The voltage dependence, kinetics, and inactivation properties of the LTS were characteristic of a low-threshold calcium spike. The threshold of the LTS was slightly above the resting potential but well below the Na spike threshold, and the LTS was often evoked in isolation in normal medium. Tetraethylammonium (TEA) and 4-aminopyridine (4-AP) had only minimal effects on the LTS but revealed the presence of a high-threshold Ca2+ spike (HTS), which was antagonized by Cd2+. The LTS displayed paired-pulse attenuation, with a timescale for recovery from inactivation of about 2 s at resting membrane potential. The LTS strongly boosted Na spike initiation; with repetitive stimulation, the long recovery of the LTS governed Na spike initiation. Thus the olfactory granule cells possess an LTS, with intrinsic kinetics that contribute to sub- and suprathreshold responses on a timescale of seconds. This adds a new mechanism to the early processing of olfactory input.
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Affiliation(s)
- Giulietta Pinato
- Department of Medical Physiology, University of Copenhagen, DK-2200 N Copenhagen, Denmark
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24
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Abstract
T-type Ca2+ channels were originally called low-voltage-activated (LVA) channels because they can be activated by small depolarizations of the plasma membrane. In many neurons Ca2+ influx through LVA channels triggers low-threshold spikes, which in turn triggers a burst of action potentials mediated by Na+ channels. Burst firing is thought to play an important role in the synchronized activity of the thalamus observed in absence epilepsy, but may also underlie a wider range of thalamocortical dysrhythmias. In addition to a pacemaker role, Ca2+ entry via T-type channels can directly regulate intracellular Ca2+ concentrations, which is an important second messenger for a variety of cellular processes. Molecular cloning revealed the existence of three T-type channel genes. The deduced amino acid sequence shows a similar four-repeat structure to that found in high-voltage-activated (HVA) Ca2+ channels, and Na+ channels, indicating that they are evolutionarily related. Hence, the alpha1-subunits of T-type channels are now designated Cav3. Although mRNAs for all three Cav3 subtypes are expressed in brain, they vary in terms of their peripheral expression, with Cav3.2 showing the widest expression. The electrophysiological activities of recombinant Cav3 channels are very similar to native T-type currents and can be differentiated from HVA channels by their activation at lower voltages, faster inactivation, slower deactivation, and smaller conductance of Ba2+. The Cav3 subtypes can be differentiated by their kinetics and sensitivity to block by Ni2+. The goal of this review is to provide a comprehensive description of T-type currents, their distribution, regulation, pharmacology, and cloning.
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Affiliation(s)
- Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908-0735, USA.
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