In addition to G proteins, GIRK channels are activated by alcohols16–18. In order to address whether this property is retained in the purified protein, we examined the effect of directly applying ethanol to GIRK2-containing liposomes with brain PIP2. Ethanol, added at increasing concentrations, produced a dose-dependent increase in the relative rate of K+ flux (Fig. 3a). Similarly, increasing concentrations of propanol also enhanced the relative rate of K+ flux (Fig. 3b). We calculated the change in the rate of K+ flux, relative to 0 mM alcohol, and plotted the normalized rate as a function of alcohol concentration (Fig. 3c). Note the increase in the normalized rate of K+ flux with concentrations greater than 10 mM, a rank order of activation with propanol greater than ethanol, and no apparent saturation at 200 mM. These properties of alcohol activation are remarkably similar to those with GIRK2 channels expressed heterologously in HEK293 cells16–18. Importantly, alcohol-dependent activation required brain PIP2 (Fig. 3d). Thus, we show for the first time that alcohol-dependent activation of GIRK channels requires only PIP2, and no other proteins, e.g., Gβγ subunits.
