Effects of tranexamic acid on the activity of glutamate transporter EAAT3

Background: Tranexamic acid (TXA) is the most widely used hemostatic agent in surgical patients. However, when used in a high dose, it could cause a seizure in the postoperative period. The exact effector mechanism behind the seizure triggering remains unknown. Therefore, the authors investigated the effects of TXA on the activity of glutamate transporter type 3 (excitatory amino acid transporter 3; EAAT3), which is the main neuronal glutamate transporter type. Methods: EAAT3 was expressed in Xenopus laevis oocytes through mRNA injection. Oocytes were incubated with diluted tranexamic acid for 72 h. Two-electrode voltage clamping was used to measure membrane currents before, during, and after applying 30 M L-glutamate. Responses were quantified by integrating the current traces and reported in microcoulombs (C). Results were presented as mean  SEM.Results: TXA (30 to 1,000 M) significantly decreased EAAT3 activity. Our kinetic study showed that Vmax was significantly decreased in the TXA group compared with the control group (1.1  0.1 vs. 1.4  0.1 C, n = 18–23, P = 0.043), but the Km did not significantly change (12.7  3.9 M for TXA vs. 12.8  3.8 for control, n = 18–23, P = 0.986).Conclusions: Our results suggest that TXA attenuates EAAT3 activity, which may explain its proconvulsant effect.