Fig. 6

Real-time imaging of intracellular K⁺ fluxes. a Representative single cell K⁺ (blue solid line) and Ca²⁺ (red dashed line) response of an INS-1 cell expressing lc-LysM GEPII 1.0 and CAR-GECO1 upon cell depolarization using 70 mM KCl (n = 9 independent measurements/32 cells/32 cells responded as demonstrated). b Columns represent maximal ∆FRET ratio signals ± SD of INS-1 cells expressing cytosolic lc-LysM GEPII 1.0 upon depolarization under control conditions (ctrl, white bar, n = 17/96), in the absence of extracellular Ca²⁺ (1 mM EGTA, black bar, n = 7/50), in the presence of 15 mM TEA (blue bar, n = 6/50), in the presence of 100 µM nifedipine (green bar, n = 6/41), and in cells loaded with BAPTA-AM (red bar, n = 6/53). ***P < 0.0001, one-way ANOVA test with Tukey’s Multiple Comparison Test. c Schemes demonstrating the activation of K⁺ efflux via a plasma membrane K⁺ channel by Ca²⁺ entry and points of action of pharmacological inhibitors. d Representative confocal images of cytosolic, subplasmalemmal, nuclear and mitochondrially targeted lc-LysM GEPII 1.0 in INS-1 cells (upper images). Scale bar represents 20 µm. Representative single cell responses of cytosolic (n = 7/53/53), subplasmalemmal (n = 7/56/56), nuclear (n = 7/30/23), and mitochondrially (n = 7/45/33) targeted lc-LysM GEPII 1.0 upon cell depolarization using 70 mM KCl (lower panels)