Cystic fibrosis transmembrane conductance regulator mediates sulphonylurea block of the inwardly rectifying K+ channel Kir6.1

摘要

class="enumerated" style="list-style-type:decimal">Recombinant ATP-sensitive K⁺ channels (KATP channels) were heterologously expressed in the NIH3T3 mouse cell line, and the electrophysiological properties were studied using patch-clamp techniques.The NIH3T3 cell lines transfected with the inwardly rectifying K⁺ channel Kir6.1 alone or with both Kir6.1 and cystic fibrosis transmembrane conductance regulator (CFTR) exhibited time-independent K⁺ currents with weak inward rectification. In contrast, no measurable K⁺ conductance was observed in mock-transfected cells or in cells transfected with CFTR alone. Regardless of co-transfection with Kir6.1, the transfection with CFTR produced a Cl⁻ conductance that was activated by cell dialysis with cAMP (1 mm). The conductance was reversibly suppressed by glibenclamide (30 μm).Whole-cell currents at +60 mV were blocked in a concentration-dependent manner by Ba²⁺ ions with similar IC50 values: 89.3 ± 23.3 μm (Kir6.1 alone) and 67.3 ± 24.9 μm (Kir6.1-CFTR).The currents recorded from Kir6.1-transfected cells were not affected by glibenclamide, whereas glibenclamide did inhibit the conductance expressed in cells co-transfected with CFTR (IC50= 35.9 ± 6.6 μm).In the cell-attached mode with a 150 mm K⁺ pipette solution, both Kir6.1- and Kir6.1-CFTR-transfected cells displayed a class of K⁺ channels showing weak inward rectification and a slope conductance of 50.7 ± 1.0 and 52.4 ± 4.9 pS, respectively.In the inside-out mode, the single-channel currents recorded from both types of cells were not inhibited by intracellular ATP (1 mm). However, glibenclamide was found to block the single-channel activities in the co-transfected cells.