| Ion channels are proteins that control the flow of ions in and out of the cell. They are important in many aspects of human physiology such as muscle contraction, sensory perception, thought and behavior. Ethanol is the most common drug of abuse worldwide. Ethanol modulates numerous ion channels, but the exact mechanism of modulation has been elusive. My dissertation investigates how ethanol and other alcohols modulate the activity of G-protein gated inwardly rectifying potassium (GIRK) channels.;GIRK channels are members of the inwardly rectifying potassium channel family that regulate the resting membrane potential of excitable cells. They are ubiquitously expressed in the brain and the heart. In the neurons, opening of GIRK channel leads to inhibition of neuronal firing. Ethanol activates GIRK channel in neurons. However, exactly how ethanol activates GIRK channels is not known.;In this dissertation, I first used structure-based mutagenesis and electrophysiology to determine that alcohols act on a hydrophobic pocket in the cytoplasmic domain of GIRK channels resulting in channel activation. To strengthen this finding, I used thiol modifying reagents targeted to the hydrophobic pocket to show that this pocket is important for activation of GIRK channels.;To determine the mechanism of this alcohol mediated activation of GIRK channels, I studied the requirement of G-proteins and PIP2 and found that alcohol activates GIRK channels in a G-protein independent, but PIP2 dependent manner. I then studied single channel properties of alcohol activated GIRK channels. I found that alcohols increase the frequency of channel opening. Combining structural models and functional data, I present a novel model for alcohol mediated activation of GIRK channels. In this model, alcohol facilitates spontaneous opening of GIRK channels by binding to the hydrophobic alcohol pocket and opening its cytoplasmic gate. This work contributes to our fundamental understanding of how ethanol modulates ion channels and how GIRK channels are gated. |
