Inhibition of voltage-gated calcium channels by fluoxetine in rat hippocampal pyramidal cells

Fluoxetine, an antidepressant which is used world-wide, is a prominent member of the class of selective serotonin re-uptake inhibitors. Recently, inhibition of voltage-gated Na + and K + channels by fluoxetine has also been reported. We examined the effect of fluoxetine on voltage-gated calcium channels using the patch-clamp technique in the whole-cell configuration. In hippocampal pyramidal cells, fluoxetine inhibited the low-voltage-activated (T-type) calcium current with an IC 50 of 6.8 μM. Fluoxetine decreased the high-voltage-activated (HVA) calcium current with an IC 50 between 1 and 2 μM. Nifedipine and ω-conotoxin GVIA inhibited the HVA current by 24% and 43%, respectively. Fluoxetine (3 μM), applied in addition to nifedipine or ω-conotoxin, further reduced the current. When fluoxetine (3 μM) was applied first neither nifedipine nor ω-conotoxin attenuated the remaining component of the HVA current. This observation indicates that fluoxetine inhibits both L- and N-type currents. In addition, fluoxetine inhibited the HVA calcium current in carotid body type I chemoreceptor cells and pyramidal neurons prepared from prefrontal cortex. In hippocampal pyramidal cells high K +-induced seizure-like activity was inhibited by 1 μM fluoxetine; the mean burst duration was shortened by an average of 44%. These results provide evidence for inhibition of T-, N- and L-type voltage-gated calcium channels by fluoxetine at therapeutically relevant concentrations.