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Purkinje Cells as Sources of Arrhythmias in Long QT Syndrome Type 3.

Iyer V, Roman-Campos D, Sampson KJ, Kang G, Fishman GI, Kass RS - Sci Rep (2015)

Bottom Line: Isolated ventricular myocytes (VMs) (EGFP(-)) and PCs (EGFP(+)) from wild type and ΔKPQ mutant hearts were compared using the whole-cell patch clamp technique and microfluorimetry of calcium transients.Marked prolongation of action potential duration of ΔKPQ-PCs was seen compared to ΔKPQ-VMs. ΔKPQ-PCs, but not ΔKPQ-VMs, exhibited frequent early afterdepolarizations, which corresponded to repetitive oscillations of intracellular calcium.We present the first direct experimental evidence that PCs are uniquely sensitive to LQT3 mutations, displaying electrophysiological behavior that is highly pro-arrhythmic.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Columbia University Medical Center, New York, NY.

ABSTRACT
Long QT syndrome (LQTS) is characterized by ventricular arrhythmias and sudden cardiac death. Purkinje cells (PC) within the specialized cardiac conduction system have unique electrophysiological properties that we hypothesize may produce the primary sources of arrhythmia in heritable LQTS. LQTS type 3 (LQT3) transgenic mice harboring the ΔKPQ(+/-) mutation were crossed with Contactin2-EGFP BAC transgenic mice, which express a fluorescent reporter gene within the Purkinje fiber network. Isolated ventricular myocytes (VMs) (EGFP(-)) and PCs (EGFP(+)) from wild type and ΔKPQ mutant hearts were compared using the whole-cell patch clamp technique and microfluorimetry of calcium transients. Increased late sodium current was seen in ΔKPQ-PCs and ΔKPQ-VMs, with larger density in ΔKPQ-PCs. Marked prolongation of action potential duration of ΔKPQ-PCs was seen compared to ΔKPQ-VMs. ΔKPQ-PCs, but not ΔKPQ-VMs, exhibited frequent early afterdepolarizations, which corresponded to repetitive oscillations of intracellular calcium. Abnormalities in cell repolarization were reversed with exposure to mexiletine. We present the first direct experimental evidence that PCs are uniquely sensitive to LQT3 mutations, displaying electrophysiological behavior that is highly pro-arrhythmic.

No MeSH data available.


Related in: MedlinePlus

Action potentials recorded from ΔKPQ-PCs (N = 20, 5 animals) show three different behaviors.Panel (A) Representative action potentials with essentially stable morphology and duration (N = 3 cells demonstrated this behavior). Panel (B) Representative action potentials with marked variation of morphology and duration from beat to beat (N = 9 cells demonstrated this behavior). Panel (C) Example action potentials with intermittent failure of repolarization before arrival of a subsequent stimulus (N = 8 cells demonstrated this behavior). APD: action potential duration.
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f3: Action potentials recorded from ΔKPQ-PCs (N = 20, 5 animals) show three different behaviors.Panel (A) Representative action potentials with essentially stable morphology and duration (N = 3 cells demonstrated this behavior). Panel (B) Representative action potentials with marked variation of morphology and duration from beat to beat (N = 9 cells demonstrated this behavior). Panel (C) Example action potentials with intermittent failure of repolarization before arrival of a subsequent stimulus (N = 8 cells demonstrated this behavior). APD: action potential duration.

Mentions: Only a minority of ΔKPQ-PCs showed stable AP morphology from sweep to sweep (Fig. 3A for representative stable APs). Instead, the characteristic behavior of ΔKPQ-PCs was profound beat-to-beat variability in AP duration and morphology (Fig. 3B). At least 10 consecutive sweeps per cell (and as many as 50, if the cell showed stable recordings) were used for each cell analyzed. We identified all cells that showed >50 ms difference in APD90 between the longest and shortest APs recorded during these sweeps. This degree of variation occurred in 17/20 ΔKPQ-PCs, compared with 0/12 ΔKPQ-VMs, 3/16 WT-PCs, and 0/16 WT-VMs (p < 0.01 for ΔKPQ-PC vs. all other groups; p = NS for WT-PC vs. both VM groups). In many cells, ΔKPQ-PCs intermittently failed to completely repolarize before the next stimulus, indicating an APD of at least 1000 ms (note second stimulus in Fig. 3C occurs during the extended plateau phase of first AP). This failure to repolarize occurred in 8/20 ΔKPQ-PCs, and was not seen in any other cell type.


Purkinje Cells as Sources of Arrhythmias in Long QT Syndrome Type 3.

Iyer V, Roman-Campos D, Sampson KJ, Kang G, Fishman GI, Kass RS - Sci Rep (2015)

Action potentials recorded from ΔKPQ-PCs (N = 20, 5 animals) show three different behaviors.Panel (A) Representative action potentials with essentially stable morphology and duration (N = 3 cells demonstrated this behavior). Panel (B) Representative action potentials with marked variation of morphology and duration from beat to beat (N = 9 cells demonstrated this behavior). Panel (C) Example action potentials with intermittent failure of repolarization before arrival of a subsequent stimulus (N = 8 cells demonstrated this behavior). APD: action potential duration.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4542521&req=5

f3: Action potentials recorded from ΔKPQ-PCs (N = 20, 5 animals) show three different behaviors.Panel (A) Representative action potentials with essentially stable morphology and duration (N = 3 cells demonstrated this behavior). Panel (B) Representative action potentials with marked variation of morphology and duration from beat to beat (N = 9 cells demonstrated this behavior). Panel (C) Example action potentials with intermittent failure of repolarization before arrival of a subsequent stimulus (N = 8 cells demonstrated this behavior). APD: action potential duration.
Mentions: Only a minority of ΔKPQ-PCs showed stable AP morphology from sweep to sweep (Fig. 3A for representative stable APs). Instead, the characteristic behavior of ΔKPQ-PCs was profound beat-to-beat variability in AP duration and morphology (Fig. 3B). At least 10 consecutive sweeps per cell (and as many as 50, if the cell showed stable recordings) were used for each cell analyzed. We identified all cells that showed >50 ms difference in APD90 between the longest and shortest APs recorded during these sweeps. This degree of variation occurred in 17/20 ΔKPQ-PCs, compared with 0/12 ΔKPQ-VMs, 3/16 WT-PCs, and 0/16 WT-VMs (p < 0.01 for ΔKPQ-PC vs. all other groups; p = NS for WT-PC vs. both VM groups). In many cells, ΔKPQ-PCs intermittently failed to completely repolarize before the next stimulus, indicating an APD of at least 1000 ms (note second stimulus in Fig. 3C occurs during the extended plateau phase of first AP). This failure to repolarize occurred in 8/20 ΔKPQ-PCs, and was not seen in any other cell type.

Bottom Line: Isolated ventricular myocytes (VMs) (EGFP(-)) and PCs (EGFP(+)) from wild type and ΔKPQ mutant hearts were compared using the whole-cell patch clamp technique and microfluorimetry of calcium transients.Marked prolongation of action potential duration of ΔKPQ-PCs was seen compared to ΔKPQ-VMs. ΔKPQ-PCs, but not ΔKPQ-VMs, exhibited frequent early afterdepolarizations, which corresponded to repetitive oscillations of intracellular calcium.We present the first direct experimental evidence that PCs are uniquely sensitive to LQT3 mutations, displaying electrophysiological behavior that is highly pro-arrhythmic.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Columbia University Medical Center, New York, NY.

ABSTRACT
Long QT syndrome (LQTS) is characterized by ventricular arrhythmias and sudden cardiac death. Purkinje cells (PC) within the specialized cardiac conduction system have unique electrophysiological properties that we hypothesize may produce the primary sources of arrhythmia in heritable LQTS. LQTS type 3 (LQT3) transgenic mice harboring the ΔKPQ(+/-) mutation were crossed with Contactin2-EGFP BAC transgenic mice, which express a fluorescent reporter gene within the Purkinje fiber network. Isolated ventricular myocytes (VMs) (EGFP(-)) and PCs (EGFP(+)) from wild type and ΔKPQ mutant hearts were compared using the whole-cell patch clamp technique and microfluorimetry of calcium transients. Increased late sodium current was seen in ΔKPQ-PCs and ΔKPQ-VMs, with larger density in ΔKPQ-PCs. Marked prolongation of action potential duration of ΔKPQ-PCs was seen compared to ΔKPQ-VMs. ΔKPQ-PCs, but not ΔKPQ-VMs, exhibited frequent early afterdepolarizations, which corresponded to repetitive oscillations of intracellular calcium. Abnormalities in cell repolarization were reversed with exposure to mexiletine. We present the first direct experimental evidence that PCs are uniquely sensitive to LQT3 mutations, displaying electrophysiological behavior that is highly pro-arrhythmic.

No MeSH data available.


Related in: MedlinePlus