Permeability characteristics of monovalent cations in atrial myocytes of the rat heart

Youm, Jae Boum; Ho, Won‐Kyung; Earm, Yung E.

doi:10.1017/s0958067000019515

Cited by 3 publications

(5 citation statements)

References 23 publications

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“…Therefore, Cl Ϫ flux was not involved in the Cs ϩ current recordings. In rat atrial myocytes, it has been reported that under isotonic Cs ϩ (140 mM) conditions a current through the nonselective cation channels existed in the presence of 5 M E-4031 and 1 M nicardipine (52). In the present study, the Cs ϩ current from rabbit ventricular myocytes was completely abolished by 1 M astemizole, 5 M cisapride, or 30 M E-4031.…”

Section: Discussionsupporting

confidence: 51%

“…The major K ϩ currents in rabbit ventricular myocytes include I to , I K1 , I Kr , and I Ks (7,8,33). Because the permeability of Cs ϩ through most voltage-gated K ϩ channels seems to be negligible (15), high Cs ϩ permeability through hERG/I Kr (39,51,52,54) provides a unique way to isolate I Kr from other currents.…”

Section: Discussionmentioning

confidence: 99%

“…Cs ϩ permeability in rat atrial myocytes has been thought to be due to the Cs ϩ permeation through I Kr (52). The mechanism underlying the high Cs ϩ permeability in hERG/I Kr channels is not known.…”

Section: Discussionmentioning

confidence: 99%

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Isolation and characterization of I_Kr in cardiac myocytes by Cs⁺ permeation

Zhang¹

2006

American Journal of Physiology-Heart and Circulatory Physiology

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Isolation of the rapidly activating delayed rectifier potassium current (I(Kr)) from other cardiac currents has been a difficult task for quantitative study of this current. The present study was designed to separate I(Kr) using Cs+ in cardiac myocytes. Cs+ have been known to block a variety of K+ channels, including many of those involved in the cardiac action potential such as inward rectifier potassium current I(K1) and the transient outward potassium current I(to). However, under isotonic Cs+ conditions (135 mM Cs+), a significant membrane current was recorded in isolated rabbit ventricular myocytes. This current displayed the voltage-dependent onset of and recovery from inactivation that are characteristic to I(Kr). Consistently, the current was selectively inhibited by the specific I(Kr) blockers. The biophysical and pharmacological properties of the Cs+-carried human ether-a-go-go-related gene (hERG) current were very similar to those of the Cs+-carried I(Kr) in ventricular myocytes. The primary sequence of the selectivity filter in hERG was in part responsible for the Cs+ permeability, which was lost when the sequence was changed from GFG to GYG, characteristic of other, Cs+-impermeable K+ channels. Thus the unique high Cs+ permeability in I(Kr) channels provides an effective way to isolate I(Kr) current. Although the biophysical and pharmacological properties of the Cs+-carried I(Kr) are different from those of the K+-carried I(Kr), such an assay enables I(Kr) current to be recorded at a level that is large enough and sufficiently robust to evaluate any I(Kr) alterations in native tissues in response to physiological or pathological changes. It is particularly useful for exploring the role of reduction of I(Kr) in arrhythmias associated with heart failure and long QT syndrome due to the reduced hERG channel membrane expression.

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Section: Discussionsupporting

confidence: 51%

Section: Discussionmentioning

confidence: 99%

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Isolation and characterization of I_Kr in cardiac myocytes by Cs⁺ permeation

Zhang¹

2006

American Journal of Physiology-Heart and Circulatory Physiology

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“…This also points to the contamination of the whole cell currents by endogenously expressed other currents, which can be activated in parallel with the TRPM7-like current, and may have an impact on E rev . Despite Cs + -based internal and external solutions helped for various K + channels elimination, nevertheless, at least one of them, such as rapid delayed rectifying K + channel, is permeable to Cs + [23], and this could be the reason for such negative E rev under experimental conditions used. The averaged current density of both type records at positive and negative potentials is presented in Figure 1C and D (plane white and grey columns on the left), respectively.…”

Section: Resultsmentioning

confidence: 99%

Characterization of Mg2+-regulated TRPM7-like current in human atrial myocytes

et al. 2012

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BackgroundTRPM7 (Transient Receptor Potential of the Melastatin subfamily) proteins are highly expressed in the heart, however, electrophysiological studies, demonstrating and characterizing these channels in human cardiomyocytes, are missing.MethodsWe have used the patch clamp technique to characterize the biophysical properties of TRPM7 channel in human myocytes isolated from right atria small chunks obtained from 116 patients in sinus rhythm during coronary artery and valvular surgery. Under whole-cell voltage-clamp, with Ca2+ and K+ channels blocked, currents were generated by symmetrical voltage ramp commands to potentials between -120 and +80 mV, from a holding potential of -80 mV.ResultsWe demonstrate that activated native current has dual control by intracellular Mg2+ (free-Mg2+ or ATP-bound form), and shows up- or down-regulation by its low or high levels, respectively, displaying outward rectification in physiological extracellular medium. High extracellular Mg2+ and Ca2+ block the outward current, while Gd3+, SpM4+, 2-APB, and carvacrol inhibit both (inward and outward) currents. Besides, divalents also permeate the channel, and the efficacy sequence, at 20 mM, was Mg2+>Ni2+>Ca2+>Ba2+>Cd2+ for decreasing outward and Ni2+>Mg2+>Ba2+≥Ca2+>Cd2+ for increasing inward currents. The defined current bears many characteristics of heterologously expressed or native TRPM7 current, and allowed us to propose that current under study is TRPM7-like. However, the time of beginning and time to peak as well steady state magnitude (range from 1.21 to 11.63 pA/pF, ncells/patients = 136/77) of induced TRPM7-like current in atrial myocytes from different patients showed a large variability, while from the same sample of human atria all these parameters were very homogenous. We present new information that TRPM7-like current in human myocytes is less sensitive to Mg2+. In addition, in some myocytes (from 24 out of 77 patients) that current was already up-regulated at membrane rupture.ConclusionsThis study provides the first electrophysiological description of TRPM7-like current in native human atrial myocytes. Less sensitivity to intracellular Mg2+ suggests for channel operation under physiological conditions. The TRPM7-like current up-regulation indicates the pathophysiological evidence of that current in human heart.

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“…Pipette and bath solutions containing equimolar Cs + in patch-clamp experiments have been used before in HEK-hERG cells ( Zhang et al, 2003 ; Zhang, 2006 ), rabbit ventricular cardiomyocytes ( Zhang, 2006 ), neonatal rat ventricular myocytes ( Dennis et al, 2012 ), canine ventricular myocytes ( Nalos et al, 2011 ), and iPSC-CM ( Goversen et al, 2019 ). The important advantage of Cs + over K + is that cesium blocks most other ion channels in the heart ( Youm et al, 2000 ). This allows the recording of relatively pure hERG channel-specific currents.…”

Section: Introductionmentioning

confidence: 99%

Recording ten-fold larger IKr conductances with automated patch clamping using equimolar Cs+ solutions

Bloothooft,

Verbruggen,

Seibertz

et al. 2024

Front. Physiol.

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Background: The rapid delayed rectifier potassium current (IKr) is important for cardiac repolarization and is most often involved in drug-induced arrhythmias. However, accurately measuring this current can be challenging in human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes because of its small current density. Interestingly, the ion channel conducting IKr, hERG channel, is not only permeable to K+ ions but also to Cs+ ions when present in equimolar concentrations inside and outside of the cell.Methods: In this study, IhERG was measured from Chinese hamster ovary (CHO)-hERG cells and hiPSC-CM using either Cs+ or K+ as the charge carrier. Equimolar Cs+ has been used in the literature in manual patch-clamp experiments, and here, we apply this approach using automated patch-clamp systems. Four different (pre)clinical drugs were tested to compare their effects on Cs+- and K+-based currents.Results: Using equimolar Cs+ solutions gave rise to approximately ten-fold larger hERG conductances. Comparison of Cs+- and K+-mediated currents upon application of dofetilide, desipramine, moxifloxacin, or LUF7244 revealed many similarities in inhibition or activation properties of the drugs studied. Using equimolar Cs+ solutions gave rise to approximately ten-fold larger hERG conductances. In hiPSC-CM, the Cs+-based conductance is larger compared to the known K+-based conductance, and the Cs+ hERG conductance can be inhibited similarly to the K+-based conductance.Conclusion: Using equimolar Cs+ instead of K+ for IhERG measurements in an automated patch-clamp system gives rise to a new method by which, for example, quick scans can be performed on effects of drugs on hERG currents. This application is specifically relevant when such experiments are performed using cells which express small IKr current densities in combination with small membrane capacitances.

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Permeability characteristics of monovalent cations in atrial myocytes of the rat heart

Cited by 3 publications

References 23 publications

Isolation and characterization of I_Kr in cardiac myocytes by Cs⁺ permeation

Isolation and characterization of I_Kr in cardiac myocytes by Cs⁺ permeation

Characterization of Mg2+-regulated TRPM7-like current in human atrial myocytes

Recording ten-fold larger IKr conductances with automated patch clamping using equimolar Cs+ solutions

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Permeability characteristics of monovalent cations in atrial myocytes of the rat heart

Cited by 3 publications

References 23 publications

Isolation and characterization of IKr in cardiac myocytes by Cs+ permeation

Isolation and characterization of IKr in cardiac myocytes by Cs+ permeation

Characterization of Mg2+-regulated TRPM7-like current in human atrial myocytes

Recording ten-fold larger IKr conductances with automated patch clamping using equimolar Cs+ solutions

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Isolation and characterization of I_Kr in cardiac myocytes by Cs⁺ permeation

Isolation and characterization of I_Kr in cardiac myocytes by Cs⁺ permeation