A, representative currents (from n = 3-5 patches) recorded from inside-out membrane patches containing Kir6.2ΔN2−30ΔC25 channels alone (above), or with SUR1 (below) at -50 mV in Kint solution (see Methods). Patches were exposed to differing [ATP] as shown. B, steady-state dependence of membrane current relative to current in zero ATP (mean ±s.e.m., n = 3-5 patches for each construct) on [ATP] for wild-type and Kir6.2ΔC25 mutant channels (as indicated). The data were fitted as described in Fig. 3. Ki = 12 μM (wild-type), 128 μM (Kir6.2ΔC25 alone), 14.0 μM (Kir6.2ΔC25 + SUR1), 117 μM (Kir6.2ΔN2−30ΔC25 alone) and 94 μM (Kir6.2ΔN2−30ΔC25 + SUR1).