The Impact of Cholesterol on GIRK Channels depends on a Transmembrane Region of the Channels

Abstract

In recent years, cholesterol emerged as a major regulator of ion channel function. The most common effect of cholesterol on ion channels is a decrease in channel activity. Here we focus on G-protein gated inwardly rectifying potassium (GIRK or Kir3) channels that play an important role in regulating membrane excitability in cardiac, neuronal and endocrine cells.We have recently shown that unexpectedly cholesterol enrichment up-regulates GIRK activity in atrial myocytes. In accordance, we also observed elevated GIRK currents in cholesterol-enriched Xenopus oocytes expressing the GIRK1/GIRK4 heteromers, the two pore-forming subunits expressed in the heart. Interestingly, whereas similarly to the heteromer GIRK1/GIRK4, the highly active homomeric pore mutant GIRK4∗ (GIRK4_S143T) was also enhanced by cholesterol, GIRK1∗ (GIRK1_F137S) was suppressed by cholesterol. Thus, in this study, we focused on identifying what determines whether a channel would be enhanced or suppressed by cholesterol.Although the major difference between these channels is in the cytosolic domain, our data showed that the impact of cholesterol did not depend on the extended C-terminus of GIRK1 as compared with GIRK4. Rather, our results show that a transmembrane region that includes residues from both the inner and outer alpha helices of the channel determines the impact of cholesterol on the channel.