Oscillatory Ca²⁺ signaling in somatostatin-producing cells from the human pancreas☆

Abstract 

Oscillatory Ca²⁺ signaling was studied in human somatostatin-releasing pancreatic δ cells identified by immunostaining. A ratiometric fura-2 technique was used for measuring cytoplasmic concentrations of Ca²⁺ and Sr²⁺ in δ cells exposed to the respective cation. Rhythmic activity in terms of slow (frequency, 0.1 to 0.4 per minute) oscillations from close to the basal level was seen in the presence of 3 to 20 mmol/L glucose during superfusion with medium containing 2.6 to 5 mmol/L Ca²⁺ or 5 mmol/L Sr². These oscillations could be transformed into a sustained increase by decreasing extracellular Ca²⁺ or adding 1 mmol/L tolbutamide or 20 nmol/L glucagon. Addition of glucagon to a medium containing 20 mmol/L glucose resulted in the generation of short (< 30 seconds) transients, which disappeared upon exposure to 100 nmol/L of the intracellular Ca²⁺-adenosine triphosphatase (ATPase) inhibitor thapsigargin. When analyzing small aggregates of islet cells, it became evident that oscillatory activity in δ cells can be synchronous with that in adjacent non—δ cells. It is concluded that secretion of pancreatic somatostatin in man involves Ca²⁺ signaling similar to that regulating the pulsatile release of insulin.

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