Patch-clamp characterisation of somatostatin-secreting δ-cells in intact mouse pancreatic islets

1. perforated patch whole-cell configuration of the patch-clamp technique was applied to superficial cells in intact mouse pancreatic islets. 2. Three types of electrical activity were observed corresponding to alpha-, beta- and delta -cells. The delta -cells were electrically active in the presence of glucose but lacked the oscillatory pattern seen in the beta -cells. By contrast, the alpha -cells were electrically silent at high glucose concentrations but action potentials could be elicited by removal of the sugar. 3. Both alpha- and beta -cells contained transient voltage-activated K+ currents. In the delta -cells, the K+ currents activated above -20 mV and were completely blocked by TEA (20 mM). The alpha -cells differed from the delta -cells in possessing a TEA-resistant K+ current activating already at -40 mV. 4. Immunocytochemistry revealed the presence of Kv3.4 channels in beta -cells and TEA-resistant Kv4.3 channels in alpha -cells. Thus the presence of a transient TEA-resistant current can be used to functionally separate the delta- and alpha -cells. 5. TX-sensitive Na+ current developed in delta -cells during depolarisations beyond -30 mV and reached a peak amplitude of 350 pA. Steady-state inactivation of this current was half-maximal at -28 mV. The delta -cells were also equipped with a sustained Ca2+ current that activated above -30mV and reached a peak of 60 pA when measrured at 2.6mM extracellular Ca2+. 6. A tolbutamide-sensitive K-ATP channel conductance was observed in delta -cells exposed to glucose-free medium. Addition of tolbutamide (0.1 mM) depolarised the delta -cell and evoked electrical activity. We propose that the K-ATP channels in delta -cells serve the same function as in the p-cell and couple an elevation of the blood glucose concentration to stimulation of hormone release.