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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

Response of △KPQ-PCs to mexiletine for a cell with wide variability of action potential morphology and duration (panel (A)), and a cell with near failure to repolarize (panel (B)). Data shown representative of N = 8 cells from 3 animals, as summarized in text.
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f4: Response of △KPQ-PCs to mexiletine for a cell with wide variability of action potential morphology and duration (panel (A)), and a cell with near failure to repolarize (panel (B)). Data shown representative of N = 8 cells from 3 animals, as summarized in text.

Mentions: Given the increased INaL, marked APD prolongation, beat-to-beat variability of repolarization, and intermittent failure to repolarize in ΔKPQ-PCs, we analyzed the response of these cells to 20 μM mexiletine. Figure 4 shows the response of ΔKPQ-PC APs to mexiletine at 1 Hz, revealing marked shortening of APD90 by 149.4 +/− 42.5 ms (p < 0.01, values in Supplement Table). Indeed, post-mexiletine ΔKPQ-PC APD90 was not different from WT-PC values (p = NS for comparison). Mexiletine also almost completely eliminated APD variability in ΔKPQ-PCs (8/8 cells with at least 50 ms APD variability before mexiletine, 1/8 cells post-mexiletine, p < 0.01). As expected, mexiletine also reduced INaL at 1 Hz in ΔKPQ-PCs by 66% (−2.12 +/− 0.20 pA/pF to −0.72 +/− 0.10 pA/pF) and in ΔKPQ-VMs by 66% (−0.79 +/− 0.11 pA/pF to −0.27 +/− 0.04 pA/pF).


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)

Response of △KPQ-PCs to mexiletine for a cell with wide variability of action potential morphology and duration (panel (A)), and a cell with near failure to repolarize (panel (B)). Data shown representative of N = 8 cells from 3 animals, as summarized in text.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Response of △KPQ-PCs to mexiletine for a cell with wide variability of action potential morphology and duration (panel (A)), and a cell with near failure to repolarize (panel (B)). Data shown representative of N = 8 cells from 3 animals, as summarized in text.
Mentions: Given the increased INaL, marked APD prolongation, beat-to-beat variability of repolarization, and intermittent failure to repolarize in ΔKPQ-PCs, we analyzed the response of these cells to 20 μM mexiletine. Figure 4 shows the response of ΔKPQ-PC APs to mexiletine at 1 Hz, revealing marked shortening of APD90 by 149.4 +/− 42.5 ms (p < 0.01, values in Supplement Table). Indeed, post-mexiletine ΔKPQ-PC APD90 was not different from WT-PC values (p = NS for comparison). Mexiletine also almost completely eliminated APD variability in ΔKPQ-PCs (8/8 cells with at least 50 ms APD variability before mexiletine, 1/8 cells post-mexiletine, p < 0.01). As expected, mexiletine also reduced INaL at 1 Hz in ΔKPQ-PCs by 66% (−2.12 +/− 0.20 pA/pF to −0.72 +/− 0.10 pA/pF) and in ΔKPQ-VMs by 66% (−0.79 +/− 0.11 pA/pF to −0.27 +/− 0.04 pA/pF).

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