Ethanol Increases Neuronal Firing by Regulating PI(4,5)P2 Sensitivity of M-Type K+ Channels

Abstract

Ethanol affects the physiological functions of the central nerve systems by changing signaling pathways through the plasma membrane or by altering the membrane electrical properties. It has been reported that ethanol regulates neuronal firing by changing the gating of ion channels, including GIRK, BK, CaV, NaV and M-type potassium channels. It has been known that the M-type KCNQ2/3 channels require the membrane phosphoinositide phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for their activation. Although various studies on the physiological effects of ethanol has been reported, molecular mechanisms of the ethanol regulation on KCNQ2/3 channel gating and neuronal activity have not been studied well. Here, we have examined the molecular mechanisms for ethanol regulation of M-type KCNQ2/3 current and membrane excitability in SCG neurons. First, our data show that 100 mM and 400 mM concentrations of ethanol inhibits M-current in SCG neurons by ∼20% and ∼65%, respectively. Similar responses are found in tsA201 cells expressing the KCNQ2/3 channels. We also found that the ethanol inhibition is decreased when the cells are co-transfected with the PI(4,5)P2 synthesizing kinase PIPKIγ (∼8% inhibition in 400 mM ethanol-treated cells). In addition, KCNQ2 or KCNQ3 homomeric channels show different ethanol sensitivity, where KCNQ2 and KCNQ3 homomeric currents were inhibited by ∼40% and ∼10%, respectively, upon 200 mM ethanol application. Those results suggest that membrane PI(4,5)P2 plays an important regulator in the ethanol suppression of M-channels. In consistent, ethanol application increased neuronal firing in all three classes of SCG neurons sorted by their firing patterns (phasic-1, phasic-2 and tonic neuron). Taken together, our results suggest that ethanol elevates neuronal firing in the sympathetic SCG neurons by suppressing the M-channel activity via the suppression of PI(4,5)P2 sensitivity of KCNQ channel proteins.