Time‐Dependent Effects of Ethanol on BKChannel Expression and Trafficking in Hippocampal Neurons

The large conductance Ca2+‐ and voltage‐activated K+channel (BK) is an important player in molecular and behavioral alcohol tolerance. Trafficking and surface expression of ion channels contribute to the development of addictive behaviors. We have previously reported that internalization of the BKchannel is a component of molecular tolerance to ethanol (EtOH). Using primary cultures of hippocampal neurons, we combine total internal reflection fluorescence microscopy, electrophysiology, and biochemical techniques to explore how exposure to EtOHaffects the expression and subcellular localization of endogenous BKchannels over time. Exposure to EtOHchanged the expression of endogenous BKchannels in a time‐dependent manner at the perimembrane area (plasma membrane and/or the area adjacent to it), while total protein levels of BKremain unchanged. These results suggest a redistribution of the channel within the neurons rather than changes in synthesis or degradation rates. Our results showed a temporally nonlinear effect of EtOHon perimembrane expression of BK. First, there was an increasein BKperimembrane expression after 10 minutes of EtOHexposure that remained evident after 3 hours, although not correlated to increases in functional channel expression. In contrast, after 6 hours of EtOHexposure, we observed a significant decreasein both BKperimembrane expression and functional channel expression. Furthermore, after 24 hours of EtOHexposure, perimembrane levels of BKhad returned to baseline. We report a complex time‐dependent pattern in the effect of EtOHon BKchannel trafficking, including successive increases and decreases in perimembrane expression and a reduction in active BKchannels after 3 and 6 hours of EtOHexposure. Possible mechanisms underlying this multiphasic trafficking are discussed. As molecular tolerance necessarily underlies behavioral tolerance, the time‐dependent alterations we see at the level of the channel may be relevant to the influence of drinking patterns on the development of behavioral tolerance.