KCNE beta subunits determine pH sensitivity of KCNQ1 potassium channels.

BACKGROUND/AIMS: Heteromeric KCNEx/KCNQ1 (=KvLQT1, Kv7.1) K(+) channels are important for repolarization of cardiac myocytes, endolymph secretion in the inner ear, gastric acid secretion, and transport across epithelia. They are modulated by pH in a complex way: homomeric KCNQ1 is inhibited by external acidification (low pH(e)); KCNE2/KCNQ1 is activated; and for KCNE1/KCNQ1, variable effects have been reported. METHODS: The role of KCNE subunits for the effect of pH(e) on KCNQ1 was analyzed in transfected COS cells and cardiac myocytes by the patch-clamp technique. RESULTS: In outside-out patches of transfected cells, hKCNE2/hKCNQ1 current was increased by acidification down to pH 4.5. Chimeras with the acid-insensitive hKCNE3 revealed that the extracellular N-terminus and at least part of the transmembrane domain of hKCNE2 are needed for activation by low pH(e). hKCNE1/hKCNQ1 heteromeric channels exhibited marked changes of biophysical properties at low pH(e): The slowly activating hKCNE1/hKCNQ1 channels were converted into constitutively open, non-deactivating channels. Experiments on guinea pig and mouse cardiac myocytes pointed to an important role of KCNQ1 during acidosis implicating a significant contribution to cardiac repolarization under acidic conditions. CONCLUSION: External pH can modify current amplitude and biophysical properties of KCNQ1. KCNE subunits work as molecular switches by modulating the pH sensitivity of human KCNQ1.