GABAA receptors meet all the pharmacological criteria required to be considered important general anaesthetic targets. In the following study, the modulatory effects of various commercially available and novel cyclohexanols were investigated on recombinant human γ-aminobutyric acid (GABAA, α1β2γ2s) receptors expressed in Xenopus oocytes, and compared to the modulatory effects on GABA currents observed with exposures to the intravenous anaesthetic agent, propofol. Submaximal EC20 GABA currents were typically enhanced by co-applications of 3–300 μM cyclohexanols. For instance, at 30 μM 2,6-diisopropylcyclohexanol (a novel compound) GABA responses were increased ~ 3-fold (although similar enhancements were achieved at 3 μM propofol). As regards rank order for modulation by the cyclohexanol analogues at 30 μM, the % enhancements for 2,6-dimethylcyclohexanol ~ 2,6-diethylcyclohexanol ~ 2,6-diisopropylcyclohexanol ~ 2,6-di-sec-butylcyclohexanol ≫2,6-di-tert-butylcyclohexanol ~ 4-tert-butylcyclohexanol > cyclohexanol ~ cyclopentanol ~ 2-methylcyclohexanol.
We further tested the potencies of the cyclohexanol analogues as general anaesthetics using a tadpole in vivo assay. Both 2,6-diisopropylcyclohexanol and 2,6-dimethylcyclohexanol were effective as anaesthetics with EC50s of 14.0 μM and 13.1 μM respectively, while other cyclohexanols with bulkier side chains were less potent. In conclusion, our data indicate that cyclohexanols are both positive modulators of GABAA receptors currents and anaesthetics. The positioning and size of the alkyl groups at the 2 and 6 positions on the cyclohexanol ring were critical determinants of activity. |
