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1 Two electrode voltage clamp and single channel recordings were used to investigate the actions of various ATP-sensitive K + (K ATP ) channel inhibitors on cloned K ATP channels, expressed in Xenopus oocytes and HEK 293 cells. 2 Oocytes expressing Kir6.2 and SUR1 gave rise to inwardly rectifying K + currents following bath application of 3 mM sodium azide. Inside-out recordings from non-azide treated oocytes demonstrated the presence of K ATP channels which were activated by direct application of 3 mM azide and 0.1 mM Mg-ATP. 3 Tolbutamide inhibited azide-induced macroscopic Kir6.2-SUR1 currents, recorded from Xenopus oocytes, with an IC 50 value similar to native K ATP channels. Ciclazindol and englitazone also inhibited these currents in a concentration-dependent manner, but with relative potencies substantially less than for native K ATP channels. 4 Single channel currents recorded from inside-out patches excised from oocytes expressing Kir6.2-SUR1 currents were inhibited by tolbutamide, Mg-ATP, englitazone and ciclazindol, in the absence of azide, with potencies similar to native K ATP channels. In the presence of azide, Kir6.2-SUR1 currents were inhibited by englitazone and tolbutamide but not ciclazindol. 5 Single channel currents derived from Kir6.2D26, expressed in HEK 293 cells, were inhibited by ciclazindol and englitazone irrespective of the absence or presence of SUR1. 6 In conclusion, heterologously expressed Kir6.2 and SUR1 recapitulate the pharmacological pro®le of native pancreatic b-cell K ATP channels. However, currents induced by azide exhibit a substantially reduced sensitivity to ciclazindol. It is likely that ciclazindol and englitazone inhibit K ATP currents by interaction with the Kir6.2 subunit.

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