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Hegyi B, Horváth B, Váczi K, Gönczi M, Kistamás K, Ruzsnavszky F, Veress R, Izu LT, Chen-Izu Y, Bányász T, Magyar J, Csernoch L, Nánási PP, Szentandrássy N. Ca 2+-activated Cl - current is antiarrhythmic by reducing both spatial and temporal heterogeneity of cardiac repolarization. J Mol Cell Cardiol 2017; 109:27-37. [PMID: 28668303 DOI: 10.1016/j.yjmcc.2017.06.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 06/26/2017] [Accepted: 06/28/2017] [Indexed: 01/26/2023]
Abstract
The role of Ca2+-activated Cl- current (ICl(Ca)) in cardiac arrhythmias is still controversial. It can generate delayed afterdepolarizations in Ca2+-overloaded cells while in other studies incidence of early afterdepolarization (EAD) was reduced by ICl(Ca). Therefore our goal was to examine the role of ICl(Ca) in spatial and temporal heterogeneity of cardiac repolarization and EAD formation. Experiments were performed on isolated canine cardiomyocytes originating from various regions of the left ventricle; subepicardial, midmyocardial and subendocardial cells, as well as apical and basal cells of the midmyocardium. ICl(Ca) was blocked by 0.5mmol/L 9-anthracene carboxylic acid (9-AC). Action potential (AP) changes were tested with sharp microelectrode recording. Whole-cell 9-AC-sensitive current was measured with either square pulse voltage-clamp or AP voltage-clamp (APVC). Protein expression of TMEM16A and Bestrophin-3, ion channel proteins mediating ICl(Ca), was detected by Western blot. 9-AC reduced phase-1 repolarization in every tested cell. 9-AC also increased AP duration in a reverse rate-dependent manner in all cell types except for subepicardial cells. Neither ICl(Ca) density recorded with square pulses nor the normalized expressions of TMEM16A and Bestrophin-3 proteins differed significantly among the examined groups of cells. The early outward component of ICl(Ca) was significantly larger in subepicardial than in subendocardial cells in APVC setting. Applying a typical subepicardial AP as a command pulse resulted in a significantly larger early outward component in both subepicardial and subendocardial cells, compared to experiments when a typical subendocardial AP was applied. Inhibiting ICl(Ca) by 9-AC generated EADs at low stimulation rates and their incidence increased upon beta-adrenergic stimulation. 9-AC increased the short-term variability of repolarization also. We suggest a protective role for ICl(Ca) against risk of arrhythmias by reducing spatial and temporal heterogeneity of cardiac repolarization and EAD formation.
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Affiliation(s)
- Bence Hegyi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Pharmacology, Genome and Biomedical Science Facility, University of California, Davis, 451 Health Sciences Drive, Rm 3503, Davis, CA 95616, USA
| | - Balázs Horváth
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Faculty of Pharmacy, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Krisztina Váczi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Mónika Gönczi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; MTA-DE Momentum, Laboratory of Protein Dynamics, Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Kornél Kistamás
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Ferenc Ruzsnavszky
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Roland Veress
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Leighton T Izu
- Faculty of Pharmacy, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Ye Chen-Izu
- Faculty of Pharmacy, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Biomedical Engineering, Genome and Biomedical Science Facility, University of California, Davis, 451 Health Sciences Drive, Rm 2303, Davis, CA 95616, USA; Department of Internal Medicine, Division of Cardiology, Genome and Biomedical Science Facility, University of California, Davis, 451 Health Sciences Drive, Rm 6315, Davis, CA 95616, USA
| | - Tamás Bányász
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - János Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Division of Sport Physiology, Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - László Csernoch
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
| | - Péter P Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary.
| | - Norbert Szentandrássy
- Department of Physiology, Faculty of Medicine, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary; Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Nagyerdei krt 98, P.O. Box 22, H-4012 Debrecen, Hungary
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9-Anthracene carboxylic acid is more suitable than DIDS for characterization of calcium-activated chloride current during canine ventricular action potential. Naunyn Schmiedebergs Arch Pharmacol 2014; 388:87-100. [PMID: 25344201 DOI: 10.1007/s00210-014-1050-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/21/2014] [Indexed: 12/16/2022]
Abstract
Understanding the role of ionic currents in shaping the cardiac action potential (AP) has great importance as channel malfunctions can lead to sudden cardiac death by inducing arrhythmias. Therefore, researchers frequently use inhibitors to selectively block a certain ion channel like 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and 9-anthracene carboxylic acid (9-AC) for calcium-activated chloride current (ICl(Ca)). This study aims to explore which blocker is preferable to study ICl(Ca). Whole-cell voltage-clamp technique was used to record ICa,L, IKs, IKr and IK1, while action potentials were measured using sharp microelectrodes. DIDS- (0.2 mM) and 9-AC-sensitive (0.5 mM) currents were identical in voltage-clamp conditions, regardless of intracellular Ca(2+) buffering. DIDS-sensitive current amplitude was larger with the increase of stimulation rate and correlated well with the rate-induced increase of calcium transients. Both drugs increased action potential duration (APD) to the same extent, but the elevation of the plateau potential was more pronounced with 9-AC at fast stimulation rates. On the contrary, 9-AC did not influence either the AP amplitude or the maximal rate of depolarization (V max), but DIDS caused marked reduction of V max. Both inhibitors reduced the magnitude of phase-1, but, at slow stimulation rates, this effect of DIDS was larger. All of these actions on APs were reversible upon washout of the drugs. Increasing concentrations of 9-AC between 0.1 and 0.5 mM in a cumulative manner gradually reduced phase-1 and increased APD. 9-AC at 1 mM had no additional actions upon perfusion after 0.5 mM. The half-effective concentration of 9-AC was approximately 160 μM with a Hill coefficient of 2. The amplitudes of ICa,L, IKs, IKr and IK1 were not changed by 0.5 mM 9-AC. These results suggest that DIDS is equally useful to study ICl(Ca) during voltage-clamp but 9-AC is superior in AP measurements for studying the physiological role of ICl(Ca) due to the lack of sodium channel inhibition. 9-AC has also no action on other ion currents (ICa,L, IKr, IKs, IK1); however, ICa,L tracings can be contaminated with ICl(Ca) when measured in voltage-clamp condition.
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Saegusa N, Garg V, Spitzer KW. Modulation of ventricular transient outward K⁺ current by acidosis and its effects on excitation-contraction coupling. Am J Physiol Heart Circ Physiol 2013; 304:H1680-96. [PMID: 23585132 DOI: 10.1152/ajpheart.00070.2013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The contribution of transient outward current (Ito) to changes in ventricular action potential (AP) repolarization induced by acidosis is unresolved, as is the indirect effect of these changes on calcium handling. To address this issue we measured intracellular pH (pHi), Ito, L-type calcium current (ICa,L), and calcium transients (CaTs) in rabbit ventricular myocytes. Intracellular acidosis [pHi 6.75 with extracellular pH (pHo) 7.4] reduced Ito by ~50% in myocytes with both high (epicardial) and low (papillary muscle) Ito densities, with little effect on steady-state inactivation and activation. Of the two candidate α-subunits underlying Ito, human (h)Kv4.3 and hKv1.4, only hKv4.3 current was reduced by intracellular acidosis. Extracellular acidosis (pHo 6.5) shifted Ito inactivation toward less negative potentials but had negligible effect on peak current at +60 mV when initiated from -80 mV. The effects of low pHi-induced inhibition of Ito on AP repolarization were much greater in epicardial than papillary muscle myocytes and included slowing of phase 1, attenuation of the notch, and elevation of the plateau. Low pHi increased AP duration in both cell types, with the greatest lengthening occurring in epicardial myocytes. The changes in epicardial AP repolarization induced by intracellular acidosis reduced peak ICa,L, increased net calcium influx via ICa,L, and increased CaT amplitude. In summary, in contrast to low pHo, intracellular acidosis has a marked inhibitory effect on ventricular Ito, perhaps mediated by Kv4.3. By altering the trajectory of the AP repolarization, low pHi has a significant indirect effect on calcium handling, especially evident in epicardial cells.
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Affiliation(s)
- Noriko Saegusa
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA
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Saegusa N, Moorhouse E, Vaughan-Jones RD, Spitzer KW. Influence of pH on Ca²⁺ current and its control of electrical and Ca²⁺ signaling in ventricular myocytes. ACTA ACUST UNITED AC 2012; 138:537-59. [PMID: 22042988 PMCID: PMC3206307 DOI: 10.1085/jgp.201110658] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Modulation of L-type Ca(2+) current (I(Ca,L)) by H(+) ions in cardiac myocytes is controversial, with widely discrepant responses reported. The pH sensitivity of I(Ca,L) was investigated (whole cell voltage clamp) while measuring intracellular Ca(2+) (Ca(2+)(i)) or pH(i) (epifluorescence microscopy) in rabbit and guinea pig ventricular myocytes. Selectively reducing extracellular or intracellular pH (pH(o) 6.5 and pH(i) 6.7) had opposite effects on I(Ca,L) gating, shifting the steady-state activation and inactivation curves to the right and left, respectively, along the voltage axis. At low pH(o), this decreased I(Ca,L), whereas at low pH(i), it increased I(Ca,L) at clamp potentials negative to 0 mV, although the current decreased at more positive potentials. When Ca(2+)(i) was buffered with BAPTA, the stimulatory effect of low pH(i) was even more marked, with essentially no inhibition. We conclude that extracellular H(+) ions inhibit whereas intracellular H(+) ions can stimulate I(Ca,L). Low pH(i) and pH(o) effects on I(Ca,L) were additive, tending to cancel when appropriately combined. They persisted after inhibition of calmodulin kinase II (with KN-93). Effects are consistent with H(+) ion screening of fixed negative charge at the sarcolemma, with additional channel block by H(+)(o) and Ca(2+)(i). Action potential duration (APD) was also strongly H(+) sensitive, being shortened by low pH(o), but lengthened by low pH(i), caused mainly by H(+)-induced changes in late Ca(2+) entry through the L-type Ca(2+) channel. Kinetic analyses of pH-sensitive channel gating, when combined with whole cell modeling, successfully predicted the APD changes, plus many of the accompanying changes in Ca(2+) signaling. We conclude that the pH(i)-versus-pH(o) control of I(Ca,L) will exert a major influence on electrical and Ca(2+)-dependent signaling during acid-base disturbances in the heart.
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Affiliation(s)
- Noriko Saegusa
- Department of Physiology, Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA
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Park SJ, Choi WW, Kwon OS, Chung JH, Eun HC, Earm YE, Kim SJ. Acidic pH-activated Cl Current and Intracellular Ca Response in Human Keratinocytes. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2008; 12:177-83. [PMID: 19967053 DOI: 10.4196/kjpp.2008.12.4.177] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The layers of keratinocytes form an acid mantle on the surface of the skin. Herein, we investigated the effects of acidic pH on the membrane current and [Ca(2+)](c) of human primary keratinocytes from foreskins and human keratinocyte cell line (HaCaT). Acidic extracellular pH (pH(e)</= 5.5) activated outwardly rectifying Cl(-) current (I(Cl,pH)) with slow kinetics of voltage-dependent activation. I(Cl,pH) was potently inhibited by an anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS, 73.5% inhibition at 1 microM). I(Cl,pH) became more sensitive to pH(e) by raising temperature from 24 to 37. HaCaT cells also expressed Ca(2+)-activated Cl(-) current (I(Cl,Ca)), and the amplitude of I(Cl,Ca) was increased by relatively weak acidic pH(e) (7.0 and 6.8). Interestingly, the acidic pH(e) (5.0) also induced a sharp increase in the intracellular [Ca(2+)] (Delta[Ca(2+)](acid)) of HaCaT cells. The Delta[Ca(2+)](acid) was independent of extracellular Ca(2+), and was abolished by the pretreatment with PLC inhibitor, U73122. In primary human keratinocytes, 5 out of 28 tested cells showed Delta[Ca(2+)](acid). In summary, we found I(Cl,pH) and Delta[Ca(2+)](acid) in human keratinocytes, and these ionic signals might have implication in pathophysiological responses and differentiation of epidermal keratinocytes.
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Affiliation(s)
- Su Jung Park
- Department of Physiology, Seoul National University College of Medicine, Seoul 110-799, Korea
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Yamamoto S, Ehara T. Acidic extracellular pH-activated outwardly rectifying chloride current in mammalian cardiac myocytes. Am J Physiol Heart Circ Physiol 2005; 290:H1905-14. [PMID: 16339831 DOI: 10.1152/ajpheart.00965.2005] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Extracellular acidic pH was found to induce an outwardly rectifying Cl- current (I(Cl,acid)) in mouse ventricular cells, with a half-maximal activation at pH 5.9. The current showed the permeability sequence for anions to be SCN- > Br- > I- > Cl- > F- > aspartate, while it exhibited a time-dependent activation at large positive potentials. Similar currents were also observed in mouse atrial cells and in atrial and ventricular cells from guinea pig. Some Cl- channel blockers (DIDS, niflumic acid, and glibenclamide) inhibited ICl,acid, whereas tamoxifen had little effect on it. Unlike volume-regulated Cl- current (ICl,vol) and CFTR Cl- current (ICl,CFTR), ICl,acid was independent of the presence of intracellular ATP. Activation of ICl,acid appeared to be also independent of intracellular Ca2+ and G protein. ICl,acid and ICl,vol could develop in an additive fashion in acidic hypotonic solutions. Isoprenaline-induced ICl,CFTR was inhibited by acidification in a pH-dependent manner in guinea pig ventricular cells. Our results support the view that ICl,acid and ICl,vol stem from two distinct populations of anion channels and that the ICl,acid channels are present in cardiac cells. ICl,acid may play a role in the control of action potential duration or cell volume under pathological conditions, such as ischemia-related cardiac acidosis.
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Affiliation(s)
- Shintaro Yamamoto
- Department of Physiology, Saga University Faculty of Medicine, Saga, Japan.
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Verkerk AO, Tan HL, Ravesloot JH. Ca2+-activated Cl- current reduces transmural electrical heterogeneity within the rabbit left ventricle. ACTA ACUST UNITED AC 2004; 180:239-47. [PMID: 14962005 DOI: 10.1111/j.0001-6772.2003.01252.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Various cationic membrane channels contribute to the heterogeneity of action potential configuration between the transmural layers of the left ventricle. The role of anionic membrane channels is less intensively studied. We investigated the role of the Ca2+-activated Cl- current, ICl(Ca), in transmural electrical heterogeneity. METHODS AND RESULTS We determined the density of ICl(Ca) and its physiological role in subepicardial and subendocardial ventricular myocytes of rabbit using the patch-clamp technique. ICl(Ca) was measured as the 4,4'diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) sensitive current. The current-voltage relationships and the densities of ICl(Ca) were similar in subepicardial and subendocardial myocytes. However, the functional role of ICl(Ca) exhibited striking differences. In subendocardial myocytes, blockade of ICl(Ca) by DIDS increased action potential duration (APD) significantly at all measured stimulus frequencies (3.33-0.2 Hz). In subepicardial myocytes, ICl(Ca) blockade increased APD only at 3.33 Hz, but not at the lower stimulus frequencies. At 1 Hz, ICl(Ca) blockade in subepicardial myocytes only caused an APD increase when the transient outward K+ current, Ito1, was blocked. CONCLUSIONS The densities and gating properties of ICl(Ca) are similar in subepicardial and subendocardial myocytes. ICl(Ca) contributes to APD shortening in subendocardial, but not in subepicardial myocytes except at 3.33 Hz. These differences in functional expression of ICl(Ca) reduce the electrical heterogeneity in rabbit left ventricle.
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Affiliation(s)
- A O Verkerk
- Department of Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
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Verkerk AO, Tan HL, Kirkels JH, Ravesloot JH. Role of Ca2+-activated Cl- current during proarrhythmic early afterdepolarizations in sheep and human ventricular myocytes. ACTA ACUST UNITED AC 2004; 179:143-8. [PMID: 14510777 DOI: 10.1046/j.1365-201x.2003.01190.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
OBJECTIVES The proarrhythmic early afterdepolarizations (EADs) during phase-2 of the cardiac action potential (phase-2 EADs) are associated with secondary Ca2+-release of the sarcoplasmic reticulum. This makes it probable that the Ca2+-activated Cl- current [ICl(Ca)] is present during phase-2 EADs. Activation of ICl(Ca) during phase-2 of the action potential will result in an outwardly directed, repolarizing current and may thus be expected to prevent excessive depolarization of phase-2 EADs. The present study was designed to test this hypothesis. METHODS AND RESULTS The contribution of ICl(Ca) during phase-2 EADs was studied in enzymatically isolated sheep and human ventricular myocytes using the patch-clamp methodology. EADs were induced by a combination of a low stimulus frequency (0.5 Hz) and exposure to 1 microm noradrenaline. In sheep myocytes, the ICl(Ca) blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 0.5 mm) abolished phase-1 repolarization of the action potential in all myocytes tested. This indicates that ICl(Ca) is present in all sheep myocytes. However, DIDS had no effect on phase-2 EAD characteristics. In human myocytes, DIDS neither affected phase-1 repolarization nor phase-2 EAD characteristics. CONCLUSION In sheep ventricular myocytes, but not in human ventricular myocytes, ICl(Ca) contributes to phase-1 repolarization of the action potential. In both sheep and human myocytes, ICl(Ca) plays a limited role during phase-2 EADs.
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Affiliation(s)
- A O Verkerk
- Department of Physiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
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