Open channel block of Kv1.5 currents by citalopram

Aim: To examine whether selective serotonin reuptake inhibitor citalopram interacts with Kv1.5, one of the cardiovascular-specific Kv channel isoforms. Methods: The interaction between citalopram and Kv1.5 expressed in Chinese hamster ovary cells was studied using the whole-cell patch-clamp technique. Results: Citalopram reduced Kv1.5 whole-cell currents in a reversible concentration-dependent manner, with an IC ₅₀ value and a Hill coefficient of 2.8±1.1 mol/L and 0.8±0.3, respectively. Citalopram-induced inhibition of Kv1.5 is associated with time-dependent development of block without modifying the kinetics of current activation. The inhibition increased steeply between 30 and 0 mV, which corresponded with the voltage range for channel opening. In the voltage range positive to 0 mV, inhibition displayed an additional voltage dependence, consistent with an electrical distance δof 0.19. Citalopram slowed the deactivation time course, resulting in a tail crossover phenomenon when the tail currents, recorded in the presence and absence of citalopram, were superimposed. Inhibition of Kv1.5 by citalopram was use-dependent. Conclusion: The present results suggest that citalopram acts on Kv1.5 currents as an open-channel blocker, and much caution about arrhythmogenic risk is required when using citalopram in the treatment with depressed patients.