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

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Abstract
1 The 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 α-, β- and δ-cells. The δ-cells were electrically active in the presence of glucose but lacked the oscillatory pattern seen in the β-cells. By contrast, the α-cells were electrically silent at high glucose concentrations but action potentials could be elicited by removal of the sugar. 3 Both α- and β-cells contained transient voltage-activated K+ currents. In the δ-cells, the K+ currents activated above −20 mV and were completely blocked by TEA (20 mm). The α-cells differed from the δ-cells in possessing a TEA-resistant K+ current activating already at −40 mV. 4 Immunocytochemistry revealed the presence of Kv3.4 channels in δ-cells and TEA-resistant Kv4.3 channels in α-cells. Thus the presence of a transient TEA-resistant current can be used to functionally separate the δ- and α-cells. 5 A TTX-sensitive Na+ current developed in δ-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 δ-cells were also equipped with a sustained Ca2+ current that activated above −30 mV and reached a peak of 60 pA when measured at 2·6 mm extracellular Ca2+. 6 A tolbutamide-sensitive KATP channel conductance was observed in δ-cells exposed to glucose-free medium. Addition of tolbutamide (0·1 mm) depolarised the δ-cell and evoked electrical activity. We propose that the KATP channels in δ-cells serve the same function as in the β-cell and couple an elevation of the blood glucose concentration to stimulation of hormone release.