Open channel block of Kv1.4 potassium channels by aripiprazole

Figures

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  Fig. 1. Concentration-dependent inhibition of the Kv1.4 current by aripiprazole. (A) Representative Kv1.4 currents following the application of aripiprazole. Kv1.4 currents were evoked by 500-ms depolarizing pulses to +40 mV from a holding potential of –80 mV every 20 sec. The effects of 1, 3, 10, and 30 μM of aripiprazole are shown. The dotted line represents zero current. The inset shows first 60 ms of the traces with expanded time scale. (B) Normalized integrals of Kv1.4 currents during depolarization are plotted as a function of aripiprazole concentrations (n = 8). Data were fitted with the Hill equation (solid line). The chemical structure of aripiprazole is shown in the upper panel. (C) Inactivation kinetics (n = 8). The fast and slow components of time constants were obtained by biexponential curve fitting. (D) Time-to-peak of Kv1.4 currents (n = 8). Time constants and time-to-peak values as a function of aripiprazole concentration are shown. Data are expressed as the mean ± standard error. *p < 0.05 compared with the control.

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  Fig. 2. Voltage-dependent inhibition of Kv1.4 by aripiprazole. (A) Kv1.4 currents were evoked by a series of 500-ms depolarizing pulses between –70 and +60 mV from a holding potential of –80 mV in the absence and in the presence of 10 μM aripiprazole. The inset shows first 60 ms of the traces with expanded time scale. (B) Plots of normalized conductance (G/Gmax) versus tested membrane potentials (n = 8). Conductance (G) was calculated by dividing the peak amplitude of Kv1.4 at the test potential by assuming a reversal potential of –85 mV under the ionic conditions of our experiment. The maximal conductance (Gmax) was obtained by fitting the normalized data using a Boltzmann equation. (C) Integral currents of Kv1.4 in the presence of aripiprazole were normalized to those of the control at each voltage (n = 8). Dashed line represents the activation curve of Kv1.4 under control condition. Voltage dependence was fitted to Woodhull’s equation (see Methods): δ = 0.17 ± 0.05 (n = 8). The solid line represents the linear fit. *p < 0.05 compared with the value obtained at –30 mV.

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  Fig. 3. The effect of aripiprazole on the recovery from inactivation of Kv1.4 current. (A) Representative current traces of Kv1.4 were recorded using two-pulse protocols with varying inter-pulse intervals in the absence and presence of 10 μM aripiprazole. (B) Time course of recovery from inactivation of Kv1.4 was fitted with a single exponential function (n = 7). The peak amplitudes of the test pulse were normalized to those of pre-pulse and plotted against the inter-pulse intervals.

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  Fig. 4. Use-dependent inhibition of Kv1.4 by aripiprazole. (A) Ten repetitive 20- or 200-ms depolarizing pulses were applied to +40 mV from a holding potential of –80 mV at a frequency of 0.25 Hz under control conditions and after the application of 10 μM aripiprazole. (B) The peak amplitudes of the current at each pulse were normalized to those of the current obtained at the first pulse and then plotted as a function of the pulse number (n = 6).

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  Fig. 5. Concentration-dependent inhibition of the Kv4.3 current by aripiprazole. (A) Kv4.3 currents were evoked by a 500-ms depolarizing pulse to +40 mV from a holding potential of –80 mV every 10 sec. The effects of 1, 3, 10, and 30 μM aripiprazole are shown. The dotted line represents zero current. The inset shows first 60 ms of the traces with expanded time scale. (B) Normalized integrals of Kv4.3 currents during depolarization are plotted as a function of aripiprazole concentrations (n = 5). Data were fitted with the Hill equation (solid line).

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  Fig. 6. The effect of dehydroaripiprazole, an aripiprazole metabolite, on the Kv1.4 current. (A) Kv1.4 currents were evoked by a 500-ms depolarizing pulse to +40 mV from a holding potential of –80 mV every 20 sec in the absence and presence of dehydroaripiprazole (1–30 μM). The dotted line represents zero current. The inset shows the Kv1.4 currents on an expanded time scale for the first 60 ms of the traces. (B) Normalized integrals of Kv1.4 currents during depolarization are plotted as a function of dehydroaripiprazole concentrations (n = 5). Data were fitted with the Hill equation (solid line). The chemical structure of aripiprazole is shown in the upper panel.