Inhibition of K⁺ currents of outer hair cells in guinea pig cochlea by fluoxetine

The effects of fluoxetine (Prozac®), a widely used antidepressant drug, on K⁺ channel in outer hair cells isolated from guinea pig cochlea were studied using the whole-cell patch clamp technique. Fluoxetine potently inhibited leak K⁺ currents with an IC₅₀ of 0.78 μM. The inhibition was reversible and voltage-independent. At 45- to 103-fold higher concentrations than the plasma levels, fluoxetine reversibly blocked voltage-activated K⁺ currents. Kinetics of the current in the presence of fluoxetine resembled the control current, and the inhibition was not use-dependent. Neither the activation curve nor the reversal potential was affected by fluoxetine. This inhibition was voltage-dependent with an electric distance (δ value) of the binding site of at least 26% of the membrane field from the cytoplasmic side. Use-independent inhibition suggests that fluoxetine blocks the channel before its opening or instantly blocks the open channel. This is the first study of the action of this compound on K⁺ channel of outer hair cells of the mammalian inner ear. We conclude that the block of the leak K⁺ currents can occur at therapeutic levels of fluoxetine. Since the voltage-activated K⁺ currents are not potently blocked by fluoxetine, this action might not be related to its antidepressant action or adverse effects.