Block by fluoxetine of volume-regulated anion channels

1 We have used the whole-cell patch clamp technique to study the effect of fluoxetine, a commonly used antidepressant drug, on the volume-regulated anion channel (VRAC) in calf pulmonary artery endothelial (CPAE) cells. We also examined its effects on other Cl- channels, i.e. the Ca2+-activated Cl- current (I-Cl . Ca,) and the cystic fibrosis transmembrane conductance regulator (CFTR) to assess the specificity of this compound for VRAC. 2 At pH 7.4 fluoxetine induced a East and reversible block of the volume-sensitive chloride current (I-Cl.swell), with a K-i value of 6.0 +/- 0.5 mu M (n = 6-9]. The blocking efficiency increased with increasing extracellular pH (K-i = 0.32 +/- 0.01 mu M at pH 8.8, n = 3-9), indicating that the blockade is mediated by the uncharged form of fluoxetine. 3 Fluoxetine inhibited Ca2+-activated Cl- currents, I-Cl . Ca activated by loading CPAE cells via the patch pipette with 1000 nM free Ca2+ (K-i = 10.7 +/- 1.6 mu M at pH 7.4, n = 3-5). The CFTR channel, transiently transfected in CPAE cells, was also inhibited with a K-i value of 26.9 +/- 9.4 mu M at pH 7.4 (n = 3). 4 This study describes for the first time the effects of fluoxetine on anion channels. Our data reveal a potent block of VRAC at fluoxetine concentrations close to plasma concentrations. The results suggest a hydrophobic interaction with high affinity between uncharged fluoxetine and volume-activated chloride channels. Ca2+-activated Cl- currents and CFTR are also blocked by fluoxetine, revealing a novel characteristic of the drug as a chloride channel modulator.