Membrane potential and membrane currents were recorded from single mouse pancreatic beta-cells using the perforated patch whole-cell recording technique at 30 degrees C. Single beta-cells maintained in primary tissue culture exhibited glucose-dependent electrical activity similar to that reported for freshly isolated intact islets. The resting input conductance (5.1 +/- 0.9 nS) was determined by ATP-regulated K+ (KATP) channels as it was blocked by 1 mM tolbutamide. 8 mM glucose decreased the input conductance by 80%. The input conductance at -70 mV was of a similar value during the plateau phase and during the silent phase of electrical activity in 8 mM glucose. This suggests that oscillations of KATP channel activity do not underlie the slow waves.