Requirement of multiple protein domains and residues for gating KATP channels by intracellular pH

ATP-sensitive K+ channels (K-ATP) are regulated by pH in addition to ATP, ADP, and phospholipids. In the study we found evidence for the molecular basis of gating the cloned K-ATP by intracellular protons. Systematic constructions of chimerical Kir6.2-Kir1.1 channels indicated that full pH sensitivity required the N terminus, C terminus, and M2 region. Three amino acid residues were identified in these protein domains, which are Thr-71 in the N terminus, Cys-166 in the M2 region, and His-175 in the C terminus. Mutation of any of them to their counterpart residues in Kir1.1 was sufficient to completely eliminate the pH sensitivity. Creation of these residues rendered the mutant channels clear pH-dependent activation. Thus, critical players in gating K-ATP by protons are demonstrated. The pH sensitivity enables the K-ATP to regulate cell excitability in a number of physiological and pathophysiological conditions when pH is low but ATP concentration is normal.