Novel 384-Well Population Patch Clamp Electrophysiology Assays for Ca2+-Activated K+ Channels

Planar array electrophysiology techniques were applied to assays for modulators of recombinant hIK and hSK3 Ca 2+ -activated K + channels. In CHO-hIK–expressing cells, under asymmetric K + gradients, small-molecule channel activators evoked time- and voltage-independent currents characteristic of those previously described by classical patch clamp electrophysiology methods. In single-hole (cell) experiments, the large cell-to-cell heterogeneity in channel expression rendered it difficult to generate activator concentration-response curves. However, in population patch clamp mode, in which signals are averaged from up to 64 cells, well-to-well variation was substantially reduced such that concentration-response curves could be easily constructed. The absolute EC 50 values and rank order of potency for a range of activators, including 1-EBIO and DC-EBIO, corresponded well with conventional patch clamp data. Activator responses of hIK and hSK3 channels could be fully and specifically blocked by the selective inhibitors TRAM-34 and apamin, with IC 50 values of 0.31 µM and 3 nM, respectively. To demonstrate assay pre