Inhibitory effects of the atypical antipsychotic, clozapine, on voltage-dependent K⁺ channels in rabbit coronary arterial smooth muscle cells

Figures

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  Fig. 1. Inhibitory effect of clozapine on voltage-dependent K+ (Kv) currents in rabbit coronary artery smooth muscle cells. Kv current traces were obtained in response to 600-ms step-depolarizing pulses from a holding potential of −80 mV in the (A) absence or (B) presence of 10 μM clozapine using the same cells. (C) The current–voltage (I–V) curves of the steady-state Kv currents in the absence (○) and presence (●) of 10 μM clozapine. n = 8. The “n” means the number of cells. Only one cell was used from a rabbit to reduce individual differences. Data are mean ± SEM. *p < 0.05 (control vs. clozapine, at each voltage).

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  Fig. 2. Concentration dependence of the effects of clozapine on voltage-dependent K+ (Kv) currents. Current recordings of Kv channels were elicited by 600-ms one-step depolarizing pulses of +60 mV from a holding potential of −80 mV. (A) Superimposed current traces of Kv currents with increasing concentration of clozapine. (B) Concentration dependence of the inhibitory effect of clozapine. The inhibition (%) of Kv currents measured at the end of pulses is plotted against the clozapine concentration. The smooth line shows the best fit with a Hill equation. n = 11. Data are mean ± SEM.

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  Fig. 3. Lack of effect of clozapine on voltage dependence of steady-state activation and inactivation curve. (A) Activation curves of the voltage-dependent K+ (Kv) currents in the absence (○) and presence (●) of 10 μM clozapine. The tail currents were evoked by a returning potential of −40 mV after 20–50 ms short depolarizing pulses at different voltages. n = 9. (B) Inactivation curves of the Kv currents in the absence (○) and presence (●) of 10 μM clozapine. The curves were elicited by a returning potential of +40 mV after 7-sec depolarizing pulses at different voltages. n = 9. Data are mean ± SEM.

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  Fig. 4. Use (state)-dependent inhibitory effect of clozapine on voltage-dependent K+ (Kv) channels. Twenty repetitive depolarizing pulses from −80 to +60 mV with a duration of 150 ms were applied at frequencies of (A) 1 Hz and (B) 2 Hz, in the absence (○) and presence (●) of 10 μM clozapine. The peak currents of the Kv channels were normalized relative to the maximal peak current generated by the first pulse, and then plotted against the pulse numbers. n = 11. Data are mean ± SEM. *p < 0.05 (control vs. clozapine, at each pulse number).

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  Fig. 5. Time course of recovery from clozapine-induced inhibition of voltage-dependent K+ (Kv) channels. The recovery time constants were measured by applying an identical twin pulse, as shown in the inset. A 150-ms depolarizing pre-pulse from −80 to +60 mV was followed by an identical second pulse with increasing intervals from 30 ms to 7 sec. Solid lines represent recovery of Kv currents in the absence (○) and presence (●) of 10 μM clozapine. n = 5. Data are mean ± SEM. *p < 0.05 (control vs. clozapine, at each time point).

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  Fig. 6. Inhibitory effects of clozapine on voltage-dependent K+ (Kv)1.5, Kv2.1, and Kv7 subtypes. The representative Kv currents were elicited by applying 600-ms one-step depolarizing pulses of +60 mV from a holding potential of −80 mV. (A) Kv currents under control conditions, in the presence of DPO-1, and DPO-1 + clozapine. (B) Summary of the effects of DPO-1 on the inhibitory effect of clozapine on Kv currents. n = 5. NS, not significant (DPO-1 vs. DPO-1 + clozapine). (C) Kv currents under control conditions, in the presence of guangxitoxin, and in the presence of guangxitoxin + clozapine. (D) Summary of the effects of guangxitoxin on the inhibitory effect of clozapine on Kv currents. n = 4. *p < 0.05 (guangxitoxin vs. guangxitoxin + clozapine). (E) Kv currents under control conditions, in the presence of linopirdine, and in the presence of linopirdine + clozapine. (F) Summary of the effects of linopirdine on the inhibitory effect of clozapine on Kv currents. n = 5. *p < 0.05 (linopirdine vs. linopirdine + clozapine). Data are mean ± SEM.