Korean J Physiol Pharmacol.  2017 Jan;21(1):75-82. 10.4196/kjpp.2017.21.1.75.

Acepromazine inhibits hERG potassium ion channels expressed in human embryonic kidney 293 cells

• Joo YS
• Lee HJ
• Choi JS
• Sung KW

• KMID: 2371070
• DOI: http://doi.org/10.4196/kjpp.2017.21.1.75

Abstract

The effects of acepromazine on human ether-à-go-go-related gene (hERG) potassium channels were investigated using whole-cell voltage-clamp technique in human embryonic kidney (HEK293) cells transfected with hERG. The hERG currents were recorded with or without acepromazine, and the steady-state and peak tail currents were analyzed for the evaluating the drug effects. Acepromazine inhibited the hERG currents in a concentration-dependent manner with an ICâ‚…â‚€ value of 1.5 µM and Hill coefficient of 1.1. Acepromazine blocked hERG currents in a voltage-dependent manner between -40 and +10 mV. Before and after application of acepromazine, the half activation potentials of hERG currents changed to hyperpolarizing direction. Acepromazine blocked both the steady-state hERG currents by depolarizing pulse and the peak tail currents by repolarizing pulse; however, the extent of blocking by acepromazine in the repolarizing pulse was more profound than that in the depolarizing pulse, indicating that acepromazine has a high affinity for the open state of the channels, with a relatively lower affinity for the closed state of hERG channels. A fast application of acepromazine during the tail currents inhibited the open state of hERG channels in a concentration-dependent. The steady-state inactivation of hERG currents shifted to the hyperpolarized direction by acepromazine. These results suggest that acepromazine inhibits the hERG channels probably by an open- and inactivated-channel blocking mechanism. Regarding to the fact that the hERG channels are the potential target of drug-induced long QT syndrome, our results suggest that acepromazine can possibly induce a cardiac arrhythmia through the inhibition of hERG channels.

Keyword

Acepromazine; hERG currents; Long QT syndrome; Patch-clamp technique; Potassium channel

MeSH Terms

Acepromazine*
Arrhythmias, Cardiac
Humans*
Kidney*
Long QT Syndrome
Patch-Clamp Techniques
Potassium Channels*
Potassium*
Tail
Acepromazine
Potassium
Potassium Channels

Figure

• 

  Fig. 1 Concentration-dependent inhibition of hERG currents by acepromazine.(A) hERG currents were elicited by a 4-sec depolarizing pulse to +20 mV from a holding potential of –80 mV and repolarization to –50 mV for 6 sec to measure the peak tail currents in the absence and presence of acepromazine. The dotted line marks zero current. (B) Normalized hERG tail currents (Itail) to the control were plotted as a function of acepromazine concentration. The experimental data were fitted with a Hill equation. Data were expressed as the means±S.E.M.

• 

  Fig. 2 Effect of acepromazine on current-voltage (I -V) relationships.(A) Whole-cell hERG currents were evoked by depolarizing pulses from –70 mV to +60 mV for 4 sec in steps of 10 mV every 15 sec from a holding potential of –80 mV and repolarization to –50 mV for 6 sec in the absence and presence of acepromazine (1 µM). (B) The I -V relationships of the steady-state (Iss) and peak tail (Itail) currents of the hERG channels under the control conditions (○) and after the application of acepromazine (●). The Iss and Itail at each voltage in the presence of acepromazine were normalized to those in the absence of acepromazine. Itail data were fitted to a Boltzmann function. (C) The voltage-dependent block of the Itail by acepromazine was expressed as a relative current (IAcepromazine/IControl). *Significant difference from data obtained at –10 mV when compared to –40 mV (p<0.01). Data are expressed as the means±S.E.M.

• 

  Fig. 3 Interaction of acepromazine with inactivated and open state of hERG channels. (A) The hERG currents were elicited by 5-sec depolarizing pulse to +60 mV from a holding potential of –80 mV, followed by a repolarizing pulse to –40 mV for 5 sec to induce peak tail currents. Acepromazine (1 µM) was rapidly applied during the depolarizing pulse and continued to the repolarizing pulse as indicated by the hatched bar. The currents were measured at the end of depolarization pulse (▲, Iss) and at the time of peak tail currents (▼, Itail), during the drug application. The dotted line marks zero current. (B) Averaged data showed that the inhibition of Iss and Itail by acepromazine. *p<0.001 when compared to control. **p<0.001 when compared between Iss and Itail. Data are expressed as the means±S.E.M.

• 

  Fig. 4 Concentration-dependent effect of acepromazine on open state hERG channels.(A) The hERG currents were elicited by a 1-sec depolarizing pulse to +60 mV from a holding potential of –80 mV, followed by a repolarizing pulse to –40 mV for 10 sec to evoke peak tail currents. 1 sec after the start of repolarizing pulse, acepromazine was rapidly applied for 5 sec and then removed during the repolarizing pulse by fast drug application system. The bar indicates the time for the application of acepromazine. (B) Graph showed a concentration-response relationship for an open channel block of the hERG current by acepromazine. The normalized currents at the end of the drug application (▲) were plotted for the concentrations of acepromazine. The data were fitted using a Hill equation. Data were expressed as the means±S.E.M.

• 

  Fig. 5 Effect of acepromazine on steady-state inactivation of hERG channels.(A) Representative current traces showed the steady-state inactivation under the control conditions and in the presence of 1 µM acepromazine, which were evoked by a double-pulse protocol with steps of inter-stimulus repolarizing pulses. After the first 200-msec depolarizing pulse of +60 mV inducing hERG channel inactivation, 10 msec inter-stimulus step pulses from –100 to +20 mV, with a 10 mV increment were applied, followed by a second depolarizing pulse of +60 mV. (B) Normalized steady-state inactivation curves under control conditions (○) and in the presence of 1 µM acepromazine (●). Solid lines represent fitting with Boltzmann function. Data are expressed as means±S.E.M.

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