We investigated the effect of the calmodulin inhibitor and antipsychotic drug trifluoperazine on voltage-dependent K+ (Kv) channels. Ky currents were recorded by whole-cell configuration of patch clamp in freshly isolated rabbit coronary arterial smooth muscle cells. The amplitudes of Kv currents were reduced by trifluoperazine in a concentration-dependent manner, with an apparent IC50 value of 1.58 +/- 0.48 mu M. The rate constants of association and dissociation by trifluoperazine were 3.73 +/- 0.33 mu M-1 s(-1) and 5.84 +/- 1.41 s(-1), respectively. Application of trifluoperazine caused a positive shift in the activation curve but had no significant effect on the inactivation curve. Furthermore, trifluoperazine provoked use-dependent inhibition of the Kv current under train pulses (1 or 2 Hz). These findings suggest that trifluoperazine interacts with Kv current in a closed state and inhibits Kv current in the open state in a time- and use-dependent manner, regardless of its function as a calmodulin inhibitor and antipsychotic drug. (C) 2013 Elsevier Inc. All rights reserved.