[Ca]i elevation and oxidative stress induce KCNQ1 translocation from cytosol to cell surface and increase IKs in cardiac myocytes

Our goals are to simultaneously determine the 3-D distribution patterns of KCNQ1 and KCNE1 in cardiac myocytes, and to study the mechanism and functional implications for variations in KCNQ1/KCNE1 colocalization in the myocytes. We monitored distribution patterns of KCNQ1, KCNE1 and markers for subcellular compartments/organelles using immunofluorescence/confocal microscopy, and confirmed the findings in ventricular myocytes by directly observing fluorescently tagged KCNQ1-GFP and KCNE1-dsR expressed in these cells. We also monitored the effects of stress on KCNQ1-GFP and endoplasmic reticulum (ER) remodeling during live cell imaging. The data showed: (1) KCNE1 maintained a stable cell surface localization, while KCNQ1 exhibited variations in the cytosolic compartment (striations vs vesicles) and the degree of presence on cell surface, (2) the degree of cell surface KCNQ1/KCNE1 colocalization was positively correlated with IKs current density, (3) KCNQ1 and calnexin (ER marker) shared a cytosolic compartment, and (4) in response to stress ([Ca]i elevation, oxidative overload, or AT1R stimulation) KCNQ1 exited the cytosolic compartment and trafficked to cell periphery in vesicles. This was accompanied by partial ER fragmentation. We conclude that cellular milieu regulates KCNQ1 distribution in cardiac myocytes, and stressful conditions can increase IKs by inducing KCNQ1 movement to the cell surface. This represents a hitherto unrecognized mechanism by which IKs fulfills its function as a repolarization reserve in ventricular myocytes.