PT - JOURNAL ARTICLE AU - Achraf Traboulsie AU - Jean Chemin AU - Elodie Kupfer AU - Joël Nargeot AU - Philippe Lory TI - T-Type Calcium Channels Are Inhibited by Fluoxetine and Its Metabolite Norfluoxetine AID - 10.1124/mol.105.020842 DP - 2006 Jun 01 TA - Molecular Pharmacology PG - 1963--1968 VI - 69 IP - 6 4099 - http://molpharm.aspetjournals.org/content/69/6/1963.short 4100 - http://molpharm.aspetjournals.org/content/69/6/1963.full SO - Mol Pharmacol2006 Jun 01; 69 AB - Fluoxetine, a widely used antidepressant that primarily acts as a selective serotonin reuptake inhibitor, also inhibits various neuronal ion channels. Using the whole-cell patch-clamp technique, we have examined the effects of fluoxetine and norfluoxetine, its major active metabolite, on cloned low-voltage-activated T-type calcium channels (T channels) expressed in tsA 201 cells. Fluoxetine inhibited the three T channels CaV3.1, CaV3.2, and CaV3.3 in a concentration-dependent manner (IC50 = 14, 16, and 30 μM, respectively). Norfluoxetine was a more potent inhibitor than fluoxetine, especially on the CaV3.3 T current (IC50 = 5 μM). The fluoxetine block of T channels was voltage-dependent because it was significantly enhanced for T channels in the inactivated state. Fluoxetine caused a hyperpolarizing shift in steady-state inactivation, with a slower rate of recovery from the inactivated state. These results indicated a tighter binding of fluoxetine to the inactivated state than to the resting state of T channels, suggesting a more potent inhibition of T channels at physiological resting membrane potential. Indeed, fluoxetine and norfluoxetine at 1 μM strongly inhibited cloned T currents (∼50 and ∼75%, respectively) in action potential clamp experiments performed with firing activities of thalamocortical relay neurons. Altogether, these data demonstrate that clinically relevant concentrations of fluoxetine exert a voltage-dependent block of T channels that may contribute to this antidepressant's pharmacological effects.