OSCILLATORY CA2-PRODUCING CELLS FROM THE HUMAN PANCREAS( SIGNALING INSOMATOSTATIN)

Oscillatory Ca2+ signaling was studied in human somatostatin-releasing pancreatic delta cells identified by immunostaining. A ratiometric fu ra-2 technique was used for measuring cytoplasmic concentrations of Ca 2+ and Sr2+ in delta cells exposed to the respective cation, Rhythmic activity in terms of slow (frequency, 0.1 to 0.4 per minute) oscillati ons 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 Sr-2. These oscillations could be transformed into a sustained increase by decreasing extracellular Ca2+ or adding 1 mmo l/L tolbutamide or 20 nmol/L glucagon. Addition of glucagon to a mediu m 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 becam e evident that oscillatory activity in delta cells can be synchronous with that in adjacent non-delta cells. It is concluded that secretion of pancreatic somatostatin in man involves Ca2+ signaling similar to t hat regulating the pulsatile release of insulin. Copyright (C) 1997 by W.B. Saunders Company.