Voltage-gated and resting membrane currents recorded from B-cells in intact mouse pancreatic islets

1. The perforated patch whole-cell configuration of the patch-clamp techniq ue was applied to superficial cells in intact pancreatic islets. Immunostai ning in combination with confocal microscopy revealed that the superficial cells consisted of 35% insulin-secreting B-cells and 65 % non-B-cells (A- a nd D-cells). 2. Two types of cell, with distinct electrophysiological properties, could be functionally identified. One of these generated oscillatory electrical a ctivity when the islet was exposed to 10 mM glucose and had the electrophys iological characteristics of isolated B-cells maintained in tissue culture. 3. The Ca2+ current recorded from B-cells in situ was 80% larger than that of isolated B-cells. It exhibited significant (70%) inactivation during 100 ms depolarisations. The inactivation was voltage dependent and particularl y prominent during depolarisations evoking the largest Ca2+ currents. 4. Voltage-dependent K+ currents were observed during depolarisations to me mbrane potentials above -20 mV. These currents inactivated little during a 200 ms depolarisation and were unaffected by varying the holding potential between -90 and -30 mV. 5. The maximum resting conductance in the absence of glucose, which reflect s the conductance of ATP-regulated K+ (K-ATP) channels, amounted to similar to 4 nS. Glucose produced a concentration-dependent reduction of K-ATP cha nnel conductance with half-maximal inhibition observed with 5 mM glucose. 6. Combining voltage- and current-clamp recording allowed the estimation of the gap junction conductance between different B-cells. These experiments indicated that the input conductance of the B-cell at stimulatory glucose c oncentrations (similar to 1 nS) is almost entirely accounted for by couplin g to neighbouring B-cells.