Fig. 1. Functional KCNQ1 channels are located in the basolateral membrane of MDCK cells. (A) Confocal images of MDCK cells transiently transfected with KCNQ1 cDNA. The KCNQ1 antibody stains at the basolateral plasma membrane (a1,a2). The basolateral membranes were selectively biotinylated (b1,b2) in order to visualise the polarisation of the cells and the localisation of the basolateral plasma membranes. (a1-c1) A single horizontal confocal scan through the cell layer close to the basal level; (a2-c2) vertical confocal scans of the same cells. (c) Overlays of the images in a,b. Ap, apical membrane, Ba, basal membrane. Bar, 8 µm. (B) Whole-cell electrophysiology on MDCK cells. Transfected cells were held at –80 mV, subjected to 2-second depolarising pulses ranging from –80 mV to +60 mV, followed by 1-second pulses at –30 mV. As expected, KCNQ1-expressing cells showed a slowly activating voltage-dependent current at potentials more positive than –40 mV. The obtained current could be blocked by 100 µM XE991, confirming that the current is carried by a KCNQ channel. The amplitude at the end of each 2-second pulse is illustrated in a current-voltage diagram (296 pA±52 pA at +60 mV, n=5).