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.

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Reperfusion injury is characterised by significant oxidative stress. F2-isoprostanes (F2-IsoPs) and isofurans (IsoFs), the latter preferentially produced during increased oxygen tension, are recognised markers of in-vivo oxidative stress. We aimed to determine whether increasing oxygen tension during reperfusion modified levels of plasma total IsoFs and F2-IsoPs. Forty five patients undergoing upper limb surgery were randomised to receive inspired oxygen concentrations of 30%, 50% or 80% during the last 15 minutes of surgery. Venous blood samples were taken before the change in inspired oxygen, after 10 minutes (before reperfusion) and after 15 minutes (5 minutes after reperfusion). IsoFs and F2-IsoPs were measured by gas chromatography-mass spectrometry. Venous oxygen tension and hemoglobin concentrations were also measured. Plasma IsoFs and F2-IsoP levels in the 50% and 80% O2 groups were not significantly different from the 30% O2 group. In secondary analyses, using data combining all groups, levels of IsoFs, but not F2-IsoPs, associated with higher venous oxygen tension (P=0.038). Hemoglobin negatively modified the influence of oxygen tension on levels of IsoFs (P=0.014). This study has shown for the first time, that plasma IsoFs levels associate with higher oxygen tension in a human model of reperfusion, and this effect is significantly attenuated by hemoglobin.

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