Tranexamic acid, a widely used antifibrinolytic agent, causes convulsions by a gamma-aminobutyric acid(A) receptor antagonistic effect.
Application of 4-(aminomethyl)cyclohexanecarboxylic acid (tranexamic acid; TAMCA) to the central nervous system (CNS) has been shown to result in hyperexcitability and convulsions. However, the mechanisms underlying this action are unknown. In the present study, we demonstrate that TAMCA binds to the gamma-aminobutyric acid (GABA) binding site of GABA(A) receptors in membranes from rat cerebral cortex and does not interfere with N-methyl-D-aspartate receptors. Patch-clamp studies using human embryonic kidney cells transiently transfected with recombinant GABA(A) receptors composed of alpha 1 beta 2 gamma 2 subunits showed that TAMCA did not activate these receptors but dose dependently blocked GABA-induced chloride ion flux with an IC(50) of 7.1 +/- 3.1 mM. Application of TAMCA to the lumbar spinal cord of rats resulted in dose-dependent hyperexcitability, which was completely blocked by coapplication of the GABA(A) receptor agonist muscimol. These results indicate that TAMCA may induce hyperexcitability by blocking GABA-driven inhibition of the CNS.
Furtmüller
Roman
R
Brain Research Institute, University of Vienna, Vienna, Austria.
Schlag
Michael G
MG
Berger
Michael
M
Hopf
Rudolf
R
Huck
Sigismund
S
Sieghart
Werner
W
Redl
Heinz
H
D000818:Animals; D000933:Antifibrinolytic Agents / Q000378:metabolism / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D002460:Cell Line; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D018755:GABA Agonists / Q000378:metabolism; D018756:GABA Antagonists / Q000378:metabolism / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists; D006614:Hindlimb / Q000502:physiology; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009118:Muscimol / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism; D012640:Seizures / Q000139:chemically induced*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism; D014148:Tranexamic Acid / Q000378:metabolism / Q000494:pharmacology*
D000933:Antifibrinolytic Agents; D018755:GABA Agonists; D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D009118:Muscimol; D016291:Dizocilpine Maleate; D014148:Tranexamic Acid