Selective serotonin reuptake inhibitors facilitate ANO6 (TMEM16F) current activation and phosphatidylserine exposure

Anoctamin 6 (ANO6) is a member of the recently identified TMEM16/anoctamin protein family comprising Ca(2+)-activated Cl(-) channels that generate outward-rectifying ionic currents in response to intracellular Ca(2+) increase. ANO6 is also essential for Ca(2+)-dependent phospholipid scrambling required for blood coagulation. Selective serotonin reuptake inhibitors (SSRIs)--fluoxetine, sertraline, and paroxetine-that are used for the treatment of major depressive disorders can increase the risk of upper gastrointestinal bleeding after chronic treatment. However, at the earlier stage of intake, which is 1-7 days after the treatment, the possibility of blood coagulation might also increase, but transiently. Therefore, in this study, we investigated whether therapeutic SSRI concentrations affected the Cl(-) current or phospholipid scrambling activity of ANO6 by assessing ANO6 currents (I ANO6), phosphatidylserine (PS) exposure, and platelet aggregation. In the whole-cell patch mode, SSRIs facilitated Ca(2+)-dependent activation of IANO6 in ANO6-transfected cells, as evidenced by a significant decrease in the delay of IANO6 generation. On the other hand, in the inside-out patch clamp configuration, SSRIs showed an inhibitory effect on ANO6 currents, suggesting that SSRIs activate ANO6 via an indirect mechanism in intact cells. SSRIs also facilitated Ca(2+)-dependent PS exposure and α-thrombin-induced platelet aggregation. These results indicate that SSRIs at clinically relevant concentrations promote Ca(2+)-dependent activation of ANO6, which may have potential clinical implications such as the underlying mechanism of SSRI-induced adverse drug reactions.