Phlorotannin supplement (PS) is a natural hypnotic substrate that modulates γ-aminobutyric acid type A (GABAA)-benzodiazepine (BZD) receptors. However, there is a lack of functional data assessing the role of individual components of PS, such as Dieckol, as allosteric activators of GABAA receptors (GABAAR). Using the whole cell patch clamp technique, we demonstrated that PS functionally enhanced the activity of GABAA-BZD receptors in a heterologous system and in primary cultured neurons. Application of diazepam (DZP) or Dieckol (1) increased GABAAR-mediated inward current in HEK293T cells containing the α1 subunit in a dose-dependent manner, (2) which was blocked by co-treatment with the selective benzodiazepine site antagonist, flumazenil (FLZ); it also (3) increased the amplitude of GABAA-BZD receptors in primary cultured neurons, which was blocked by FLZ and (4) attenuated spontaneous activity in cultured neurons. These results indicate that PS and Dieckol act as positive allosteric activators of GABAA-BZD receptors, which might be the underlying mechanism of the sedative-hypnotic effect of PS. To our knowledge, this is the first study to directly link Dieckol-induced GABAAR activation via the BZD site binding and suppression of spontaneous neuronal activity in vitro.
Keywords: Dieckol; GABAA-benzodiazepine receptor; cultured neurons; insomnia; phlorotannin; polyphenol; sleep; therapeutic agent.