GABA(A) receptor modulation by terpenoids from Sideritis extracts.
Bottom Line: All effects measured were independent from the presence of the γ2 subunit.Following a prescreening on α1β2 GABAA receptors, a high-throughput method was used for identification of the most effective terpenoid substances on GABA-affinity of α1β2γ2 receptors expressed in transfected cell lines.We propose an allosteric modulation independent from the γ2 subunit and similar to the action of alcohols and anesthetics.
Affiliation: Department of Chemistry and Pharmacy, Food Chemistry Division, University of Erlangen-Nuernberg, Erlangen, Germany.Show MeSH
Related in: MedlinePlus
Mentions: These substances were tested for their potentiating effect on GABA-evoked currents in injected Xenopus oocytes and transfected HEK293 cells expressing α1β2 or α1β2γ2 GABAARs (Fig.2). The presence of the γ2 subunit was tested using a coapplication of Zn2+, which only inhibits α1β2 receptors (data not shown) 22, although recordings from both cell types yielded similar results arguing for an effect independent from the γ2 subunit. Application of compounds in the absence of GABA did not elicit any currents (data not shown). Pinenes had little or no modulatory effects; the current values using high concentrations (1mM) of either α-pinene or β-pinene showed only a small increase in the GABA-evoked responses of 0.35 ± 0.08 μA (compared to 0.25 ± 0.08 μA without α-pinene) and 0.35 ± 0.08 μA (compared to 0.24 ± 0.06 μA without β-pinene), in Xenopus oocytes and 1.37 ± 0.66 nA for α-pinene compared to 1.18 ±. 0.58 nA without modulator, and 0.52 ± 0.16 nA for β-pinene compared to 0.29 ± 0.07 nA for GABA alone in transfected HEK293 cells (Table1; see relative I-values of 1 μM GABA). Similarly, substances such as sabinene, α-phellandrene, and β-caryophyllene did not enhance responses (Fig.2B). A significant potentiation, however, was observed for 1-octen-3-ol, linalool, and carvacrol (Fig.2B). Therefore, carvacrol was tested in a dose-dependent manner using concentrations from 30 μM to 1 mM (Fig.2C). The relative current amplitudes compared to GABA alone showed that carvacrol at concentrations of 100 μM (1.8 fold potentiation) or greater significantly enhanced GABAergic currents (up to 4.5 fold, Fig.2D). Thus, carvacrol was among the substances identified from Sideritis, the most potent modulator on GABAARs comparable to linalool and 1-octen-3-ol (Fig.2B) 11.
Affiliation: Department of Chemistry and Pharmacy, Food Chemistry Division, University of Erlangen-Nuernberg, Erlangen, Germany.