Patch-clamp recording from pancreatic β-cells. (a) In the presence of 3 mmol/L glucose, the β-cell was depolarized, but hyperpolarized after adding 325 μmol/L diazoxide. (b) KATP channel recordings in isolated membrane patches. KATP channel activity was blocked by 100 μmol/L ATP and activated by 325 μmol/L diazoxide. Pancreatic islets were isolated by a collagenase technique, and cell suspensions were prepared as previously described . Experiments were performed on days two and three after isolation. Single-channel and whole-cell currents were recorded by means of the patch-clamp technique, by using an HEKA EPC-10 patch-clamp amplifier (HEKA Elektronik, Germany). Solutions and the set-up are the same as those described earlier by Bränström et al. . In short, membrane potential recordings were made by the perforated-patch technique by using amphotericin dissolved in DMSO, and recordings were started when RS < 60 MΩ. All experiments were performed at room temperature (approximately 22°C).