Effects of bepridil versus E-4031 on transmural ventricular repolarization and inducibility of ventricular tachyarrhythmias in the dog

Bepridil, a class IV antiarrhythmic agent, can block the TREK-1 potassium channel

Background

The TWIK-related potassium channel (TREK-1) can be regulated by different stimuli. However, it is not clear whether some antiarrhythmics affect the activity of TREK-1. In the present study, the effect of bepridil on the TREK-1 currents is investigated.

Methods

In a TREK-1 stably-expressed HEK-293 cell line (HEK-TREK-1), U251MG cells, and isolated mouse ventricular myocytes, the TREK-1 current and action potentials were recorded by the patch-clamp technique. The standard voltage protocol was a 200 ms constant potential at 20 mV, followed bya 500 ms ramp from –90 to +20 mV (HEK-TREK-1) or +80 mV (U251MG cells and myocytes) every 10 s. The currents at +20 mV or +80 mV were used for analysis. The docking study of bepridil’s binding model in the TREK-1 channel was performed using the Swissdock web service.

Results

In HEK-TREK-1 cells, BL1249 induced a significantly large outwardly rectifying current with similar baseline TREK-1 current characteristic, with a reversal potential (−70 mV). The concentration of half-maximal activation (EC₅₀) of BL1249 was 3.45 µM. However, bepridil decreased the baseline TREK-1 currents, with a concentration of half-maximal inhibition (IC₅₀) 0.59 µM and a Hill coefficient of 1.1. Also, bepridil inhibited BL1249-activated TREK-1 currents, with an IC₅₀ 4.08 µM and a Hill coefficient of 3.22. The outside-out patch-clamp confirmed bepridil inhibited BL1249-activated TREK-1 currents. In U251MG cells and myocytes, BL1249 activated outwardly rectifying endogenous TREK-1 currents, which could be inhibited by bepridil. BL1249 (10 µM) could decrease the peak value and reduce the duration of the action potential. Bepridil (10 µM) prolonged the duration of action potential of myocytes. The docking study revealed that bepridil might affect the K⁺ pore domain and the M4 modulator pocket.

Conclusions

Bepridil may be a blocker for the TREK-1K⁺channel at a clinically therapeutic concentration, providing a new mechanism of TREK-1 regulation and bepridil's antiarrhythmic effect.

Bepridil Inhibits Premature Ventricular Complexes Induced by Cardio-Sympathetic Nerve Stimulation in a Canine Experimental Model

Sympathetic nerve activity has arrhythmogenic potential for ventricular arrhythmias associated with structural heart diseases. However, a sufficient amount of beta-blockers occasionally cannot be prescribed in some patients.An experimental study was performed to clarify the therapeutic effects of bepridil, a multiple ionic current inhibitor that does not affect beta-adrenergic receptors, for premature beats occurring during enhanced sympathetic nerve activity. Cardio-sympathetic nerve activity was augmented via stellate-ganglion (SG) stimulation in a canine model (n = 8), and the arrhythmogenic potential and anti-arrhythmic effects of bepridil (2 and 4 mg/kg intravenously) were assessed. For safe use, vagal-stimulation-induced slow HR and programmed electrical stimulation were applied to evaluate possible pro-arrhythmic effects of the drug. Heart rate variability (HRV) indexes were used to estimate cardio-autonomic nerve activity.Either side of the SG-stimulation increased BP and HR. Premature beats were induced in 10/16 SG-stimulations and it was more frequent in left (8/8) rather than right stimulation (2/8). Following 2 mg/kg drug administration, premature beats were still inducible in 8/16 stimulations (7/8 in left and 1/8 in right), but burden of the premature beats decreased from 87.1 ± 46.8 to 62.1 ± 42.6 beats. After 4 mg/kg administration, premature beats were inducible in one SG-stimulation. Proarrhythmic effects were not observed in all experiments. Steady-state HRV indexes and percent increases in SG-stimulation-induced BP-elevation and HR-acceleration were similar among the 3 periods (before, 2 and 4 mg/kg of the drug).Bepridil may be an option for ventricular arrhythmias developed during enhanced cardio-sympathetic nerve activity with minimal effect on autonomic nerve responses.

In silico assessment of the effects of quinidine, disopyramide and E-4031 on short QT syndrome variant 1 in the human ventricles

Aims

Short QT syndrome (SQTS) is an inherited disorder associated with abnormally abbreviated QT intervals and an increased incidence of atrial and ventricular arrhythmias. SQT1 variant (linked to the rapid delayed rectifier potassium channel current, I_Kr) of SQTS, results from an inactivation-attenuated, gain-of-function mutation (N588K) in the KCNH2-encoded potassium channels. Pro-arrhythmogenic effects of SQT1 have been well characterized, but less is known about the possible pharmacological antiarrhythmic treatment of SQT1. Therefore, this study aimed to assess the potential effects of E-4031, disopyramide and quinidine on SQT1 using a mathematical model of human ventricular electrophysiology.

Methods

The ten Tusscher et al. biophysically detailed model of the human ventricular action potential (AP) was modified to incorporate I_Kr Markov chain (MC) formulations based on experimental data of the kinetics of the N588K mutation of the KCNH2-encoded subunit of the I_Kr channels. The modified ventricular cell model was then integrated into one-dimensional (1D) strand, 2D regular and realistic tissues with transmural heterogeneities. The channel-blocking effect of the drugs on ion currents in healthy and SQT1 cells was modeled using half-maximal inhibitory concentration (IC₅₀) and Hill coefficient (nH) values from literatures. Effects of drugs on cell AP duration (APD), effective refractory period (ERP) and pseudo-ECG traces were calculated. Effects of drugs on the ventricular temporal and spatial vulnerability to re-entrant excitation waves were measured. Re-entry was simulated in both 2D regular and realistic ventricular tissue.

Results

At the single cell level, the drugs E-4031 and disopyramide had hardly noticeable effects on the ventricular cell APD at 90% repolarization (APD₉₀), whereas quinidine caused a significant prolongation of APD₉₀. Quinidine prolonged and decreased the maximal transmural AP heterogeneity (δV); this led to the decreased transmural heterogeneity of APD across the 1D strand. Quinidine caused QT prolongation and a decrease in the T-wave amplitude, and increased ERP and decreased temporal susceptibility of the tissue to the initiation of re-entry and increased the minimum substrate size necessary to prevent re-entry in the 2D regular model, and further terminated re-entrant waves in the 2D realistic model. Quinidine exhibited significantly better therapeutic effects on SQT1 than E-4031 and disopyramide.

Conclusions

The simulated pharmacological actions of quinidine exhibited antiarrhythmic effects on SQT1. This study substantiates a causal link between quinidine and QT interval prolongation in SQT1 and suggests that quinidine may be a potential pharmacological agent for treating SQT1 patients.