scholarly journals Immediate and Delayed Response of Simulated Human Atrial Myocytes to Clinically-Relevant Hypokalemia

2021 ◽  
Vol 12 ◽  
Author(s):  
Michael Clerx ◽  
Gary R. Mirams ◽  
Albert J. Rogers ◽  
Sanjiv M. Narayan ◽  
Wayne R. Giles
Keyword(s):  
Renal Dialysis ◽  
Outward Current ◽  
Its Region ◽  
Resting Potential ◽  
Delayed Response ◽  
Electrolyte Balance ◽  
Atrial Myocytes ◽  
Electrophysiological Response ◽  
Human Atrial Myocytes ◽  
Plasma Electrolyte

Although plasma electrolyte levels are quickly and precisely regulated in the mammalian cardiovascular system, even small transient changes in K+, Na+, Ca2+, and/or Mg2+ can significantly alter physiological responses in the heart, blood vessels, and intrinsic (intracardiac) autonomic nervous system. We have used mathematical models of the human atrial action potential (AP) to explore the electrophysiological mechanisms that underlie changes in resting potential (Vr) and the AP following decreases in plasma K+, [K+]o, that were selected to mimic clinical hypokalemia. Such changes may be associated with arrhythmias and are commonly encountered in patients (i) in therapy for hypertension and heart failure; (ii) undergoing renal dialysis; (iii) with any disease with acid-base imbalance; or (iv) post-operatively. Our study emphasizes clinically-relevant hypokalemic conditions, corresponding to [K+]o reductions of approximately 1.5 mM from the normal value of 4 to 4.5 mM. We show how the resulting electrophysiological responses in human atrial myocytes progress within two distinct time frames:(i) Immediately after [K+]o is reduced, the K+-sensing mechanism of the background inward rectifier current (IK1) responds. Specifically, its highly non-linear current-voltage relationship changes significantly as judged by the voltage dependence of its region of outward current. This rapidly alters, and sometimes even depolarizes, Vr and can also markedly prolong the final repolarization phase of the AP, thus modulating excitability and refractoriness.(ii) A second much slower electrophysiological response (developing 5–10 minutes after [K+]o is reduced) results from alterations in the intracellular electrolyte balance. A progressive shift in intracellular [Na+]i causes a change in the outward electrogenic current generated by the Na+/K+ pump, thereby modifying Vr and AP repolarization and changing the human atrial electrophysiological substrate.In this study, these two effects were investigated quantitatively, using seven published models of the human atrial AP. This highlighted the important role of IK1 rectification when analyzing both the mechanisms by which [K+]o regulates Vr and how the AP waveform may contribute to “trigger” mechanisms within the proarrhythmic substrate. Our simulations complement and extend previous studies aimed at understanding key factors by which decreases in [K+]o can produce effects that are known to promote atrial arrhythmias in human hearts.

scholarly journals From ionic to cellular variability in human atrial myocytes: an integrative computational and experimental study

2018 ◽  
Vol 314 (5) ◽  
pp. H895-H916 ◽  
Author(s):  
Anna Muszkiewicz ◽  
Xing Liu ◽  
Alfonso Bueno-Orovio ◽  
Brodie A. J. Lawson ◽  
Kevin Burrage ◽  
...  
Keyword(s):  
Ion Channel ◽  
Phenotypic Variability ◽  
Right Atrial ◽  
Resting Potential ◽  
Generic Model ◽  
Atrial Myocytes ◽  
Human Atrial Myocytes ◽  
Human Cardiomyocytes ◽  
Atrial Electrophysiology ◽  
The Impact

Variability refers to differences in physiological function between individuals, which may translate into different disease susceptibility and treatment efficacy. Experiments in human cardiomyocytes face wide variability and restricted tissue access; under these conditions, computational models are a useful complementary tool. We conducted a computational and experimental investigation in cardiomyocytes isolated from samples of the right atrial appendage of patients undergoing cardiac surgery to evaluate the impact of variability in action potentials (APs) and subcellular ionic densities on Ca2+ transient dynamics. Results showed that 1) variability in APs and ionic densities is large, even within an apparently homogenous patient cohort, and translates into ±100% variation in ionic conductances; 2) experimentally calibrated populations of models with wide variations in ionic densities yield APs overlapping with those obtained experimentally, even if AP characteristics of the original generic model differed significantly from experimental APs; 3) model calibration with AP recordings restricts the variability in ionic densities affecting upstroke and resting potential, but redundancy in repolarization currents admits substantial variability in ionic densities; and 4) model populations constrained with experimental APs and ionic densities exhibit three Ca2+ transient phenotypes, differing in intracellular Ca2+ handling and Na+/Ca2+ membrane extrusion. These findings advance our understanding of the impact of variability in human atrial electrophysiology. NEW & NOTEWORTHY Variability in human atrial electrophysiology is investigated by integrating for the first time cellular-level and ion channel recordings in computational electrophysiological models. Ion channel calibration restricts current densities but not cellular phenotypic variability. Reduced Na+/Ca2+ exchanger is identified as a primary mechanism underlying diastolic Ca2+ fluctuations in human atrial myocytes.

Comparative mechanisms of 4-aminopyridine-resistant Ito in human and rabbit atrial myocytes

1995 ◽  
Vol 269 (2) ◽  
pp. H463-H472 ◽  
Author(s):  
G. R. Li ◽  
J. Feng ◽  
Z. Wang ◽  
B. Fermini ◽  
S. Nattel
Keyword(s):  
Outward Current ◽  
Pulse Frequency ◽  
Transient Outward Current ◽  
Tetraacetic Acid ◽  
Atrial Myocytes ◽  
Human Atrial Myocytes ◽  
Atrial Cells ◽  
Whole Cell Patch Clamp ◽  
Current Voltage ◽  
Rabbit Atrium

The cardiac transient outward current (Ito) has been shown in several species to consist of two components: 1) a 4-aminopyridine (4-AP)-sensitive component (Ito1) and 2) a 4-AP-resistant component (Ito2). In rabbits, Ito2 is a Ca(2+)-dependent Cl- current [ICl(Ca)]; similar mechanisms have been suggested to underlie Ito2 in human atrium. We used whole cell patch-clamp techniques to define the mechanism of Ito2 (defined as the component resistant to 5 mM 4-AP) in human atrial myocytes, with parallel experiments performed in rabbit atrial cells. In rabbit atrium, Ito2 activated more slowly than Ito1 and had a bell-shaped current-voltage of Ito with properties similar to Ito2 in the rabbit, and a similar component recorded with pipette K+ replaced by Cs+ was suppressed by the substitution of methanesulfonate for Cl- in the superfusate. In human cells, a 4-AP-resistant Ito2 was recorded at a depolarizing pulse frequency of 1 Hz, but not at 0.1 Hz. Ito2 activated rapidly and inactivated earlier than Ito1, whereas its I-V relation was linear like that of Ito1. Ryanodine had no effect on human atrial Ito. When K(+)-free pipette solutions were used, no Ito was recorded in 30 human atrial myocytes, and external Cl- replacement with methanesulfonate failed to reveal an Ito. In 13 human myocytes, isoproterenol increased ICa but failed to activate an Ito compatible with ICl(Ca). Whereas caffeine suppressed human atrial Ito, it also suppressed Ito1 [in the presence of 200 microM Cd2+ to block ICa and 5 mM intracellular ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to buffer intracellular Ca2+] in both human and rabbit atrium, indicating an action unrelated to Ca(2+)-triggered Ca2+ release. In conclusion, we were unable to demonstrate the presence of ICl(Ca) in human atrial myocytes, and the 4-AP-resistant component of Ito appeared to be due to 4-AP unblocking.

scholarly journals Patch-Clamp Recordings of Action Potentials From Human Atrial Myocytes: Optimization Through Dynamic Clamp

2021 ◽  
Vol 12 ◽  
Author(s):  
Arie O. Verkerk ◽  
Gerard A. Marchal ◽  
Jan G. Zegers ◽  
Makiri Kawasaki ◽  
Antoine H. G. Driessen ◽  
...  
Keyword(s):  
Patch Clamp ◽  
Outward Current ◽  
Current Injection ◽  
Constant Current ◽  
Resting Membrane Potential ◽  
Dynamic Clamp ◽  
Atrial Myocytes ◽  
Surgical Ablation ◽  
Human Atrial Myocytes ◽  
The Impact

Introduction: Atrial fibrillation (AF) is the most common cardiac arrhythmia. Consequently, novel therapies are being developed. Ultimately, the impact of compounds on the action potential (AP) needs to be tested in freshly isolated human atrial myocytes. However, the frequent depolarized state of these cells upon isolation seriously hampers reliable AP recordings.Purpose: We assessed whether AP recordings from single human atrial myocytes could be improved by providing these cells with a proper inward rectifier K+ current (IK1), and consequently with a regular, non-depolarized resting membrane potential (RMP), through “dynamic clamp”.Methods: Single myocytes were enzymatically isolated from left atrial appendage tissue obtained from patients with paroxysmal AF undergoing minimally invasive surgical ablation. APs were elicited at 1 Hz and measured using perforated patch-clamp methodology, injecting a synthetic IK1 to generate a regular RMP. The injected IK1 had strong or moderate rectification. For comparison, a regular RMP was forced through injection of a constant outward current. A wide variety of ion channel blockers was tested to assess their modulatory effects on AP characteristics.Results: Without any current injection, RMPs ranged from −9.6 to −86.2 mV in 58 cells. In depolarized cells (RMP positive to −60 mV), RMP could be set at −80 mV using IK1 or constant current injection and APs could be evoked upon stimulation. AP duration differed significantly between current injection methods (p < 0.05) and was shortest with constant current injection and longest with injection of IK1 with strong rectification. With moderate rectification, AP duration at 90% repolarization (APD90) was similar to myocytes with regular non-depolarized RMP, suggesting that a synthetic IK1 with moderate rectification is the most appropriate for human atrial myocytes. Importantly, APs evoked using each injection method were still sensitive to all drugs tested (lidocaine, nifedipine, E-4031, low dose 4-aminopyridine, barium, and apamin), suggesting that the major ionic currents of the atrial cells remained functional. However, certain drug effects were quantitatively dependent on the current injection approach used.Conclusion: Injection of a synthetic IK1 with moderate rectification facilitates detailed AP measurements in human atrial myocytes. Therefore, dynamic clamp represents a promising tool for testing novel antiarrhythmic drugs.

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