Muscimol Directly Activates the TREK-2 Channel Expressed in GABAergic Neurons through Its N-Terminus.

The two-pore domain K (K) channel, which is involved in setting the resting membrane potential in neurons, is an essential target for receptor agonists. Activation of the γ-aminobutyric acid (GABA) receptors (GABAR and GABAR) reduces cellular excitability through Cl influx and K efflux in neurons. Relatively little is known about the link between GABAR and the K channel. The present study was performed to identify the effect of GABAR agonists on K channel expression and activity in the neuroblastic B35 cells that maintain glutamic acid decarboxylase (GAD) activity and express GABA. TASK and TREK/TRAAK mRNA were expressed in B35 cells with a high level of TREK-2 and TRAAK. In addition, TREK/TRAAK proteins were detected in the GABAergic neurons obtained from GABA transgenic mice. Furthermore, TREK-2 mRNA and protein expression levels were markedly upregulated in B35 cells by GABAR and GABAR agonists. In particular, muscimol, a GABAR agonist, significantly increased TREK-2 expression and activity, but the effect was reduced in the presence of the GABAR antagonist bicuculine or TREK-2 inhibitor norfluoxetine. In the whole-cell and single-channel patch configurations, muscimol increased TREK-2 activity, but the muscimol effect disappeared in the N-terminal deletion mutant. These results indicate that muscimol directly induces TREK-2 activation through the N-terminus and suggest that muscimol can reduce cellular excitability by activating the TREK-2 channel and by inducing Cl influx in GABAergic neurons.