Molecular basis of transient outward K<sup>+</sup> current diversity in mouse ventricular myocytes

Guo, Weinong; Xu, Haodong; London, Barry; Nerbonne, Jeanne M.

doi:10.1111/j.1469-7793.1999.00587.x

Cited by 195 publications

(247 citation statements)

References 37 publications

(97 reference statements)

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“…Similar correlations between Kv4.x genes and I to have been documented in humans (17,28,52) and other animal species (16,17,21,25,58,59). By contrast, no regional differences in Kv4.3 expression were observed.…”

Section: Discussionsupporting

confidence: 53%

“…mRNA and protein expression of Kv1.4 was higher in the RVW versus SEP. The significance of the current produced by these channels remains unclear, but recent studies (25,39,(58)(59)(60) have suggested that in rodents this channel encodes for the slow component of I to (see below). If correct, the relative contribution of Kv1.4 channels to the total amplitude of I to recorded at low rates of stimulation is relatively small in both the RVW and SEP even after MI.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,I_toK⁺currents, and [Ca²⁺]_itransients

Kaprielian

Sah

Nguyen

et al. 2002

American Journal of Physiology-Heart and Circulatory Physiology

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(Ito) has been shown to vary between different regions of the normal myocardium and to be reduced in heart disease. In this study, we measured regional changes in action potential duration (APD), I to, and intracellular Ca 2ϩ concentration ([Ca 2ϩ ]i) transients of ventricular myocytes derived from the right ventricular free wall (RVW) and interventricular septum (SEP) 8 wk after myocardial infarction (MI). At ϩ40 mV, I to density in sham-operated hearts was significantly higher (P Ͻ 0.01) in the RVW (15.0 Ϯ 0.8 pA/pF, n ϭ 47) compared with the SEP (7.0 Ϯ 1.1 pA/pF, n ϭ 18). After MI, I to density was not reduced in SEP myocytes but was reduced (P Ͻ 0.01) in RVW myocytes (8.7 Ϯ 1.0 pA/pF, n ϭ 26) to levels indistinguishable from post-MI SEP myocytes. These changes in I to density correlated with Kv4.2 (but not Kv4.3) protein expression. By contrast, Kv1.4 expression was significantly higher in the RVW compared with the SEP and increased significantly after MI in RVW. APD measured at 50% or 90% repolarization was prolonged, whereas peak [Ca 2ϩ ]i transients amplitude was higher in the SEP compared with the RVW in sham myocytes. These regional differences in APD and [Ca 2ϩ ]i transients were eliminated by MI. Our results demonstrate that the significant regional differences in I to density, APD, and [Ca 2ϩ ]i between RVW and SEP are linked to a variation in Kv4.2 expression, which largely disappears after MI. right ventricle; septum; heart disease; contraction THERE ARE MARKED DIFFERENCES in the action potential duration (APD) in different regions of the mammalian ventricle (4,15,18,39,58). This electrical heterogeneity in normal myocardium correlates with regional differences in the Ca 2ϩ -independent transient outward K ϩ current density (I to ) (5,15,18,34,35,43) as well as in gene expression of K ϩ channels (8,16,58). APD prolongation and reductions in I to density occur in rat heart after left anterior descending coronary artery ligation (2, 43, 58), aortic banding (5, 22, 55), as well as after treatment with either catecholamine (11) or monocrotaline (32, 33). Depending on the model, the extent of I to density changes in disease may not be uniform throughout the ventricle (2, 5, 11, 22, 55), thereby leading to possible losses of electrical heterogeneity and increased susceptibility to arrhythmias (3).Aside from electrical heterogeneity, regional differences in other myocardial properties also exist. For example, systolic intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) is higher in the endocardium than in the epicardium (19,54), consistent with the notion that the endocardium may play a more important role in contraction compared with the epicardium. The underlying basis for the regional differences in contraction is currently unknown but may be related to a heterogeneous transmural expression of Ca 2ϩ handling proteins (26, 31). Alternatively, APD might also play a key role because the action potential profile is an important determinant of the inotropic state of the heart in both normal (7,42,54) and hy...

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Section: Discussionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,I_toK⁺currents, and [Ca²⁺]_itransients

Kaprielian

Sah

Nguyen

et al. 2002

American Journal of Physiology-Heart and Circulatory Physiology

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“…Action potentials were obtained from myocytes from 6-to 12-week-old mice according to published techniques (3)(4)(5).…”

Section: Methodsmentioning

confidence: 99%

Reduced intercellular coupling leads to paradoxical propagation across the Purkinje-ventricular junction and aberrant myocardial activation

Morley

Danik

Bernstein

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Ventricular tachycardia is a common heart rhythm disorder and a frequent cause of sudden cardiac death. Aberrant cell-cell coupling through gap junction channels, a process termed gap junction remodeling, is observed in many of the major forms of human heart disease and is associated with increased arrhythmic risk in both humans and in animal models. Genetically engineered mice with cardiac-restricted knockout of Connexin43, the major cardiac gap junctional protein, uniformly develop sudden cardiac death, although a detailed electrophysiological understanding of their profound arrhythmic propensity is unclear. Using voltage-sensitive dyes and high resolution optical mapping techniques, we found that uncoupling of the ventricular myocardium results in ectopic sites of ventricular activation. Our data indicate that this behavior reflects alterations in source-sink relationships and paradoxical conduction across normally quiescent Purkinje-ventricular muscle junctions. The aberrant activation profiles are associated with wavefront collisions, which in the setting of slow conduction may account for the highly arrhythmogenic behavior of Connexin43-deficient hearts. Thus, the extent of gap junction remodeling in diseased myocardium is a critical determinant of cardiac excitation patterns and arrhythmia susceptibility.arrhythmia ͉ connexin43 ͉ Purkinje fiber ͉ transgenic ͉ optical mapping E lectrical uncoupling of the murine heart by cardiac-restricted inactivation of the Connexin43 (Cx43) gap junction channel gene results in slowing of ventricular conduction velocity (CV), spontaneous ventricular arrhythmias, and sudden cardiac death (1). However, the early mortality in these conditional knockout (CKO) mice complicated mechanistic studies of arrhythmia initiation and maintenance. Therefore, by selectively breeding longer-term survivors, we recently established a subline of conditional knockout mice, termed OCKO mice, in which the Cre-dependent inactivation of Cx43 in the myocardium was temporally delayed and death from ventricular arrhythmias, although still inevitable, was correspondingly delayed on average by about a month (2). ECGs in OCKO mice during the weeks preceding their demise demonstrated that all were in normal sinus rhythm (NSR), but, surprisingly, unlike control mice, they displayed a progressive reduction in the amplitude of the QRS complex, a time-and voltage-dependent signal indicative of myocardial depolarization (2). The aim of the current study was to investigate the mechanisms through which reductions in cell-cell coupling influence cardiac electrophysiological behavior and ultimately lead to the development of ventricular tachyarrhythmias. MethodsMice. Cardiac-restricted Cx43-mutant mice have been described, as have the derivative OCKO subline, obtained by selectively breeding longer-term survivors. The OCKO mice have progressive loss of Cx43 in the ventricular myocardium without compensatory changes in the abundance of either Cx45 or Cx40 (1, 2). Control mice did not carry the Cre recombinase tr...

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“…6). The variations in the APD -18mV and in the I to amplitudes may indicate the regional heterogeneity of repolarizing K + current reported in mouse heart cells [37,38].…”

Section: Properties Of the Isolated Heart Cellsmentioning

confidence: 99%

A Simple Technique for Isolating Healthy Heart Cells from Mouse Models

Shioya

2007

J. Physiol. Sci

126

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Single heart cells of mouse models provide powerful tools for heart research. However, their isolation is not easy, and it imposes a significant bottleneck on their use in cellular studies of the heart. Aiming to overcome this problem, this report introduces a novel technique that reproducibly isolates healthy heart cells from mouse models. Using simple devices that ensure easy handling and the rapid aortic cannulation of a small mouse heart, cell isolation was done under physiological conditions without using the "KB" medium or 2,3-butanedione monoxime (BDM). The isolated cells consistently had a healthy appearance and a high viability of 75 ± 5% (mean ± SD) in Tyrode solution containing 1.8 mM Ca 2+ . After 8 h of storage at 37°C, they still had a viability of 45 ± 12%. The cells showed normal contraction properties when field-stimulated, and they generated normal action potentials and membrane currents under the whole-cell clamp condition. The β-adrenergic signal transduction of the cells was also normal when it was examined with the isoproterenol enhancement of the L-type Ca 2+ current.Key words: mouse, cardiac myocyte, contraction, action potential, ionic current.Single heart cells of mouse models provide powerful tools for heart research. In these cells, one can take advantage of the versatility of recent genetic engineering technology [1] and also of the accuracy of single-cell measurement techniques such as patch-clamp and Ca 2+ imaging. So far, molecular mechanisms of fundamental heart functions, such as excitation-contraction coupling, action potential shaping, and β-adrenergic signaling, have been successfully unveiled by using single heart cells of mouse models [2][3][4][5][6][7]. Moreover, these cells also provide a convenient platform for analyzing pathogenic mechanisms and the pathophysiology of hereditary heart diseases in molecular detail [8,9].For such single-cell studies, healthy heart cells are absolutely necessary; however, their isolation from mouse models is not easy. Surgery and aortic cannulation of a small mouse heart are hard to do and require a long time, and during that time, the heart suffers from complete ischemia. Consequently, the cells isolated from these hearts show various signs of ischemic damages, such as bizarre appearance, low viability levels, and abnormalities in their excitation and contraction properties. Cells of these kinds are hard to use for the experiment, and the data they provide are often difficult to interpret. This issue imposes a significant bottleneck on the use of mouse heart cells and is especially problematic in genetically engineered mouse models that are usually available only in limited amounts.To solve this problem, two major work-arounds have been devised and used for heart cell isolation from mouse models. One is to incubate the cells in high-K + , Ca 2+ -free "KB" medium at 4°C [10,11], and the other is to administer 10-20 mM 2,3-butanedione monoxime (BDM) in the media for cell isolation and storage [12,13]. Both workarounds proved to be...

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Molecular basis of transient outward K⁺ current diversity in mouse ventricular myocytes

Cited by 195 publications

References 37 publications

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,I_toK⁺currents, and [Ca²⁺]_itransients

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,I_toK⁺currents, and [Ca²⁺]_itransients

Reduced intercellular coupling leads to paradoxical propagation across the Purkinje-ventricular junction and aberrant myocardial activation

A Simple Technique for Isolating Healthy Heart Cells from Mouse Models

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Molecular basis of transient outward K+ current diversity in mouse ventricular myocytes

Cited by 195 publications

References 37 publications

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,ItoK+currents, and [Ca2+]itransients

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,ItoK+currents, and [Ca2+]itransients

Reduced intercellular coupling leads to paradoxical propagation across the Purkinje-ventricular junction and aberrant myocardial activation

A Simple Technique for Isolating Healthy Heart Cells from Mouse Models

Contact Info

Product

Resources

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Molecular basis of transient outward K⁺ current diversity in mouse ventricular myocytes

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,I_toK⁺currents, and [Ca²⁺]_itransients

Myocardial infarction in rat eliminates regional heterogeneity of AP profiles,I_toK⁺currents, and [Ca²⁺]_itransients