Characterisation of sulphonylurea and ATP-regulated K+ channels in rat pancreatic A-cells

We have monitored whole-cell and single channel ATP-sensitive Kf (K-ATP) currents in isolated rat glucagon-secreting pancreatic A-cells. Tolbutamide produced a concentration-dependent decrease in the whole-cell K-ATP conductance (K-i=6 mu M) and initiated action potential firing. The K+ channel opener diazoxide, but not cromakalim or pinacidil, inhibited electrical activity and increased the whole-cell K+ conductance fourfold. ATP applied to the intracellular face of the membrane inhibited KATP channel activity with a K-i of 17 mu M, an effect that could be counteracted by Mg-ADP and Mg-GDP. GTP and UTP did not affect KATP channel activity. Phosphatidylinositol 4,5-bisphosphate activated K-ATP channels inhibited by ATP after a delay of 90 s. In situ hybridisation demonstrated the expression of the mRNA encoding Kp;yp channel subunits Kir6.2 and SUR1 but not Kir6.1 and SUR2. We conclude that rat pancreatic A-cells express K-ATP channels with the nucleotide-, sulphonylurea- and K+ channel-opener sensitivities expected for a channel formed by Kir6.2 and SUR1 subunits.