Both alcohol and cholesterol activate GIRK2 channels by increasing the apparent affinity for PIP2. We next investigated the interaction between alcohol and cholesterol on GIRK2 activation. With GIRK2-containing liposomes in 5% cholesterol (a saturating concentration in our experiments), ethanol enhanced the relative K+ flux to a greater extent than for cholesterol alone or ethanol alone (Fig. 6a). The rate of K+ flux with 5% cholesterol increased over a range of ethanol concentrations (Fig. 6b). However, the dose-response curves completely overlap over the physiological range of activation, e.g., 10–100 mM, after adjusting for the choleseterol-dependent increase in the basal K+ flux (Fig. 4b), (Fig. 6b , inset). These results indicate that the effects of alcohol and cholesterol on GIRK channel are additive, suggesting these two modulators increase channel activity via separate structural sites in the channel.
