Antiarrhythmic Effects of Vernakalant in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes from a Patient with Short QT Syndrome Type 1

Abstract

(1) Background: Short QT syndrome (SQTS) may result in sudden cardiac death. So far, no drugs, except quinidine, have been demonstrated to be effective in some patients with SQTS type 1 (SQTS1). This study was designed to examine the potential effectiveness of vernakalant for treating SQTS1 patients, using human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from a patient with SQTS1. (2) Methods: Patch clamp and calcium imaging techniques were used to examine the drug effects. (3) Results: Vernakalant prolonged the action potential duration (APD) in hiPSC-CMs from a SQTS1-patient (SQTS1-hiPSC-CMs). In spontaneously beating SQTS1-hiPSC-CMs, vernakalant reduced the arrhythmia-like events induced by carbachol plus epinephrine. Vernakalant failed to suppress the hERG channel currents but reduced the outward small-conductance calcium-activated potassium channel current. In addition, it enhanced Na/Ca exchanger currents and late sodium currents, in agreement with its APD-prolonging effect. (4) Conclusions: The results demonstrated that vernakalant can prolong APD and reduce arrhythmia-like events in SQTS1-hiPSC-CMs and may be a candidate drug for treating arrhythmias in SQTS1-patients.

Keywords: antiarrhythmic drugs; arrhythmias; human-induced pluripotent stem cell-derived cardiomyocytes; short QT syndrome; vernakalant.

Figure 1

Effects of vernakalant on action potentials in SQTS1-hiPSC-CMs. (A) Representative action potential traces in absence (Ctr) and presence of 3 µM, 10 µM and 30 µM vernakalant. (B) Averaged values of action potential duration at 50% repolarization (APD50). (C) Averaged values of action potential duration at 90% repolarization (APD90). (D) Averaged values of resting membrane potential (RMP). (E) Averaged values of action potential amplitude (APA). (F) Averaged values of maximal depolarization velocity (V_max). All the action potentials were recorded at 1 Hz. Data are shown as mean ± SEM from 21 cells. The statistical significance was examined by One Way Repeated Measures ANOVA followed by Holm–Sidak method.

Figure 2

Vernakalant prolonged APD at different frequencies. (A,B) Averaged values of APD50 and APD90 at 0.5 Hz, 1 Hz, and 3 Hz in absence (Ctr) and presence of 3 µM, 10 µM and 30 µM vernakalant from 21 cells. (C,D) Percent prolongation of APD50 and APD90 by vernakalant at 0.5 Hz, 1 Hz, and 3 Hz. The values were calculated from the data in A and B. Data are shown as mean ± SEM, the statistical significance was examined by One Way Repeated Measures ANOVA followed by Holm–Sidak method. * p < 0.05, ** p < 0.01.

Figure 3

Vernakalant reduced arrhythmia-associated events. Calcium transients were measured in spontaneously beating cells. Then carbachol (10 µM) plus epinephrine (10 µM) was applied to cells to trigger arrhythmia-associated events (AAEs). In cells showing AAEs, vernakalant (Ver, 10 µM) was applied to the cell in presence of carbachol and epinephrine. (A) Representative traces of calcium transients in a cell before challenging (Ctr). (B) Representative traces of calcium transients in the cell challenged by carbachol plus epinephrine (CCh+Epi). (C) Representative traces of calcium transients in the cell in the presence of carbachol plus epinephrine and vernakalant (CCh+Epi+Ver). (D) Averaged values of AAEs per minute. CCh+Epi slowed the beating but led to small and irregularly triggered beating. The AAEs were defined as transients that are larger than 10% but smaller than 80% of the normal regular transients. Data are shown as mean ± SEM from 18 cells. p values were determined by One Way ANOVA analysis followed by Holm-Sidak method.

Figure 4

Vernakalant had no effect on L-type calcium channel currents. The L-type Ca channel currents (I_Ca-L) were evoked by the protocol indicated in A. (A) The representative traces of I_Ca-L. (B) Current-voltage relationship (I-V) curves of I_Ca-L in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (C) Mean values of I_Ca-L at 0 mV in absence (Ctr) and presence of vernakalant (Ver, 10 µM). Data are shown as mean ± SEM from 15 cells. ns implies “not significant” determined by paired t-test.

Figure 5

Vernakalant enhanced Na/Ca exchanger and late Na channel currents. The Na/Ca exchanger currents (I_NCX) were evoked by the protocol indicated in A. I_NCX was analyzed as NiCl₂ (5 mM) -sensitive currents. Peak and late Na channel currents (late I_Na) were evoked by the protocol indicated in D and late I_Na was measured at 300 ms after initiation of the depolarization pulse. TTX (30 µM) -sensitive currents were analyzed as late I_Na. (A) Representative traces of I_NCX in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (B,C) Mean values of I_NCX at 60 mV and−100 mV in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (D) Representative traces of peak and late I_Na in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (E) Mean values of peak I_Na at −40 mV in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (F) Mean values of late I_Na at −40 mV in absence (Ctr) and presence of vernakalant (Ver, 10 µM). Data are shown as mean ± SEM. p values were determined by paired t-test.

Figure 6

Vernakalant failed to affect I_Kr and I_Ks. The currents (I_Kr and I_Ks) were evoked by the protocol indicated in A and C. I_Kr was measured as Cs⁺ currents. I_Ks was analyzed as Chromalol-293B (10 µM)-sensitive currents. (A) Representative traces of I_Kr in absence (Ctr) and presence of vernakalant (Ver, 30 µM). (B) I-V curves of I_Kr in absence (Ctr) and presence of vernakalant (Ver, 30 µM). (C) Representative traces of I_Ks in absence (Ctr) and presence of vernakalant (Ver, 30 µM). (D) I-V curves of I_Ks in absence (Ctr) and presence of vernakalant (Ver, 30 µM). Data are shown as mean ± SEM.

Figure 7

Vernakalant suppressed I_SK but not I_to and I_KATP. The currents (I_to, I_KATP and I_SK) were evoked by the protocol indicated in A, D and G. I_KATP was measured as glibenclamide (10 µM) -sensitive currents. I_to was analyzed as 4-AP (5 mM) -sensitive currents. I_SK was analyzed as apamin (100 nM) -sensitive currents. (A) Representative traces of I_to at +80 mV in absence (Ctr) and presence of 30 µM vernakalant (Ver) in hiPSC-CMs from SQTS patient. (B) I-V curves of I_to in absence (Ctr) and presence of vernakalant (Ver) in hiPSC-CMs from SQTS patient. (C) Mean values of I_to at +80 mV in absence (Ctr) and presence of vernakalant (Ver) in hiPSC-CMs from SQTS patient. (D) Representative traces of I_KATP in absence (Ctr) and presence of vernakalant (Ver, 30 µM) at −120 mV. (E) I-V curves of I_KATP in absence (Ctr) and presence of vernakalant (Ver, 30 µM). (F) Mean values of I_KATP at −120 mV in absence (Ctr) and presence of vernakalant (Ver, 30 µM). (G) Representative traces of I_SK at +40 mV in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (H) I-V curves of I_SK in absence (Ctr) and presence of vernakalant (Ver, 10 µM). (I) Mean values of I_SK at +40 mV in absence (Ctr) and presence of vernakalant (Ver, 10 µM). Data are shown as mean ± SEM. p values were determined by paired t-test, ns, not significant.