Human ether-a-go-go related gene (HERG) potassium channels (IC50 = 1.0 μmol/L in HEK cells; IC50 = 42.3 μmol/L in Xenopus oocytes). [2]

Human embryonic kidney (HEK) cells expressing wild-type and mutant HERG channels were used in electrophysiological investigations, as were Xenopus laevis oocytes (two-electrode voltage clamp). With an IC50 of 1.0μM in HEK cells and 42.3μM in Xenopus oocytes, ajmaline inhibits HERG current [2].

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Ajmaline blocked HERG currents in HEK cells with an IC50 of 1.04 ± 0.1 μmol/L (Hill coefficient nH = 0.81). In Xenopus oocytes, the IC50 was 42.3 ± 11.9 μmol/L (nH = 0.95). Block onset was fast with mean time constant tau = 44.7 ± 7.5 s, reaching steady-state after 180 s; wash-out was complete but slower (tau = 307.5 ± 45.0 s). In HERG mutant channels Y652A and F656A (lacking aromatic residues in S6 domain), the inhibitory effect of 300 μmol/L ajmaline was completely abolished (relative currents 117.8±11.7% and 117.7±3.8% respectively, compared to 10.7±3.0% in wild-type). Ajmaline induced a small shift in HERG current half-maximal activation voltage from -12.6±1.7 mV (control) to -18.6±1.9 mV (p=0.02). It did not markedly affect HERG inactivation: steady-state inactivation half-maximal voltage was -67.7±2.4 mV (control) vs -70.4±2.8 mV (ajmaline, p=0.14); time constants of inactivation at -60 mV were reduced from 13.7±1.3 ms to 8.8±1.8 ms (p=0.01) and at -40 mV from 12.5±1.3 ms to 10.4±1.5 ms (p=0.04). Ajmaline block was not voltage-dependent (relative block 52.6% at -40 mV, 34.6% at 0 mV, 41.5% at +40 mV, 47.9% at +80 mV; p>0.05). Block exhibited positive frequency dependence: remaining relative currents 52.5±9.5% at 0.1 Hz, 50.9±7.6% at 1 Hz, 44.8±5.9% at 2 Hz, and 36.1±6.4% at 3 Hz (3 Hz significantly stronger than 0.1 Hz and 1 Hz, p=0.04 and p=0.03 respectively). Ajmaline blocked HERG channels in the open but not in the closed states: activating currents at 0 mV had time constant 221.3±10.5 ms, and block developed with time constant 222.7±4.3 ms. In inactivation-deficient HERG S620T mutant channels, sensitivity to ajmaline was markedly reduced: 300 μmol/L ajmaline inhibited HERG S620T currents to 76.3±4.0% vs wild-type to 10.7±3.0% (p=4.6×10^{-7}). [2]

Whole-cell patch clamp electrophysiology was performed on HEK cells stably expressing HERG channels. The bath solution contained (in mmol/L): NaCl 140, KCl 5.0, MgCl2 1.0, CaCl2 1.8, HEPES 10, glucose 10, pH adjusted to 7.4 with NaOH. The pipette solution contained: K-aspartate 100, KCl 20, MgCl2 2.0, CaCl2 1.0, EGTA 10, HEPES 10, glucose 40, pH adjusted to 7.4 with KOH. Measurements were carried out at room temperature (20-22°C). A two-step voltage protocol was used: from a holding potential of -80 mV, first step to potentials ranging from -60 mV to +80 mV in 20 mV increments (400 ms), then a return step to -120 mV (400 ms) to elicit inward tail currents. Pulse frequency was 1 Hz. Peak inward tail currents following test pulse to +40 mV were measured.
Two-microelectrode voltage clamp recordings were performed on Xenopus laevis oocytes expressing HERG channels. The low K+ solution contained (in mmol/L): KCl 5, NaCl 100, CaCl2 1.5, MgCl2 2, HEPES 10, pH adjusted to 7.4 with NaOH. Current and voltage electrodes were filled with 3 mol/L KCl solution. Tip resistance ranged from 1 to 5 MOhm. Data were low-pass filtered at 1-2 kHz (-3 dB four-pole Bessel filter) before digitalisation at 5-10 kHz. The voltage protocol: holding potential -80 mV, first pulse to potentials from -80 mV to +80 mV in 10 mV increments (400 ms), return pulse to -60 mV (400 ms) to elicit outward tail currents. For concentration-response curves, data were fitted with the Hill equation: I/I0 = 1/(1+(X/IC50)^nH). Activation and inactivation curves were fitted with Boltzmann function: Y = {1+exp[(V1/2-V)/k]}^{-1}. [2]

HEK 293 cells stably expressing HERG channels were seeded on glass cover slips 24-72 hours before use. Cells were held at -80 mV. A modified two-step voltage protocol was applied: from holding potential -80 mV, first step to potentials ranging from -60 mV to +80 mV in 20 mV increments (400 ms), then return step to -120 mV (400 ms) to elicit large inward tail currents. Peak inward tail currents after the test pulse to +40 mV were measured to quantify block. For run-up control, HERG currents increased to 124.2±6.8% within 8 min of perfusion with bath solution alone.
Xenopus oocytes (stage V and VI defolliculated) were injected with 50 nl of HERG cRNA solution (500-2000 ng/μl) using an automatic injector. Measurements were made 2-5 days after injection. Oocytes were held at -80 mV. A two-step protocol: first step to +40 mV (400 ms) to activate currents, then return step to -60 mV (400 ms) to elicit tail currents. For inactivation studies, a holding potential of +20 mV was used, with short voltage steps to potentials from -120 mV to +30 mV in 10 mV increments (15 ms), then return to +20 mV to evoke inactivating currents. For time course of inactivation: holding -80 mV, first pulse to +40 mV (900 ms), second pulse to -100 mV (16 ms), third pulse to potentials from -60 mV to +40 mV in 20 mV increments (150 ms). For closed-state inactivation experiments: long first step (3500 ms) to +40, +80 or +100 mV, then second step to 0 mV (3500 ms) to induce recovery from inactivation. For open channel block: a single long test pulse to 0 mV (3500 ms) from holding -80 mV. [2]

Therapeutic unbound plasma concentrations of ajmaline are reported to be 0.3–1.5 μmol/L. Anti-arrhythmic efficacy is optimal at plasma levels of 0.4–2.0 μg/L. [2]

Ajmaline induces cardiac output (QT) prolongation. Several cases of ajmaline-induced torsade de pointes (TdP) ventricular tachycardia have been described. Arrhythmic complications as a consequence of ajmaline overdose have been reported. Plasma protein binding of ajmaline was found to be 76 ± 9%. The free plasma concentration calculated from total therapeutic levels is 0.3–1.5 μmol/L. Ajmaline has negative inotropic effects limiting its use in patients with heart failure. Pro-arrhythmic potential due to HERG channel blockade may lead to TdP. [2]

[1]. Liquid chromatographic assay with fluorescence detection to determine ajmaline in serum from patients with suspected Brugada syndrome. J Chromatogr B Analyt Technol Biomed Life Sci. 2010;878(23):2168-2172.

[2]. Class Ia anti-arrhythmic drug ajmaline blocks HERG potassium channels: mode of action. Naunyn Schmiedebergs Arch Pharmacol. 2004;370(6):423-435.

Aymarin is an alkaloid found in the roots of Rauwolfia serpentina and other plant sources. It is a class Ia antiarrhythmic drug, its mechanism of action primarily involving altering the waveform and threshold of myocardial action potentials. Aymarin possesses potent sodium channel blocking activity and a very short half-life, making it well-suited for acute intravenous treatment. In some countries, aymarin is widely used to treat atrial fibrillation patients with Wolff-Parkinson-White syndrome and well-tolerated monomorphic ventricular tachycardia. Furthermore, it has been used for many years to treat bundle branch block and syncope to enhance cardiac conduction function. In these cases, abnormally prolonged HV intervals are considered evidence of subhistorical His bundle block, suggesting the need for a permanent pacemaker. Aymarin has been reported in Rauvolfia yunnanensis, Rauvolfia cubana, and other organisms with relevant data. Aymarin is an alkaloid found in the roots of Rauvolfia sperpentina and other plant sources. It is a class IA antiarrhythmic drug, and its mechanism of action appears to be through altering the waveform and threshold of the myocardial action potential. Drug Indications Used as an antiarrhythmic drug. Mechanism of Action Class I antiarrhythmic drugs interfere with sodium channels. Class IA drugs prolong the action potential (right shift), thereby improving abnormal heart rhythms. This drug has a high affinity for Nav1.5 sodium channels.

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Ajmaline can only be applied intravenously, usually by short infusion. Its chemical structure contains an aromatic group and two basic nitrogen atoms. The molecular mechanism of HERG blockade involves binding to the channel pore cavity at aromatic residues Tyr-652 and Phe-656, with hydrophobic feature (aromatic group for π-stacking with Phe-656) and basic nitrogen for π-cation interaction with Tyr-652. Ajmaline is a class Ia anti-arrhythmic drug that also blocks sodium currents (IC50 6.6–8.2 μmol/L from other studies, but not investigated in this paper). In guinea pig ventricular myocytes, ajmaline prolongs action potential duration and inhibits calcium currents (ICa), inwardly rectifying potassium current (IK1), and delayed rectifier potassium current (IK) at approximately 10 μmol/L (as reported from other studies). This study demonstrates that HERG blockade by ajmaline at therapeutic concentrations may contribute to both its high anti-arrhythmic efficacy and its pro-arrhythmic potential. [2]

C20H26N2O2

326.44

326.199

4360-12-7

4410-48-4 (HCl);4360-12-7;

6100671

White to off-white solid powder

1.373g/cm3

519.406ºC at 760 mmHg

189ºC

285.155ºC

1.701

1.557

2

4

1

24

570

9

CC[C@H]1[C@@H]2C[C@H]3[C@H]4[C@@]5(C[C@@H]([C@H]2[C@H]5O)N3[C@@H]1O)C6=CC=CC=C6N4C

CJDRUOGAGYHKKD-KBPCXUENSA-N

InChI=1S/C20H26N2O2/c1-3-10-11-8-14-17-20(12-6-4-5-7-13(12)21(17)2)9-15(16(11)18(20)23)22(14)19(10)24/h4-7,10-11,14-19,23-24H,3,8-9H2,1-2H3/t10-,11-,14-,15-,16-,17-,18+,19-,20+/m0/s1

(5aR,6S,8S,9S,10R,11S,11aS,12aR,13R)-9-ethyl-5-methyl-5a,6,8,9,10,11,11a,12-octahydro-5H-6,10

TachmalinSiddiqui Takycor CardiorythmineNSC 15627 Rauwolfin (+)-Ajmaline Raugalline Rauwolfine Ritmos Gilurytmal Merabitol Ignazin Rhytmaton Rytmalin

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ≥ 100 mg/mL (~306.34 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (7.66 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (7.66 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (7.66 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)