Culture duration and conditions affect the oscillations of cytoplasmic calcium concentration induced by glucose in mouse pancreatic islets

The pattern of the increase in cytoplasmic Cai2+ that glucose produces in beta cells has been reported to be highly variable. Here, we evaluated the influence of the culture duration (1-4 days) and conditions (5-10 mmol/l glucose) on Cai2+ in normal mouse islets stimulated by glucose. After 1 day of culture in 10 mmol/l glucose, a rise of the glucose concentration from 3 to 15 mmol/l induced a triphasic change of Cai2+ in the islets. A small initial decrease was followed by a large peak increase and then by regular fast oscillations (approximately 2.5/min). When the culture was prolonged to 2, 3 and 4 days, the initial decrease became inconsistent and the peak occurred earlier, whereas the oscillations decreased in frequency, increased in duration and eventually disappeared; on day 4 the Cai2+ rise was sustained. After culture in 5 mmol/l glucose, the pattern of Cai2+ changes induced by 15 mmol/l glucose was different. The initial decrease was very pronounced, the first peak was delayed and clearly separated from the subsequent oscillations. These were of a mixed type (fast Ca2+ transients on top of slow ones) after 1 day, and of a slow type only after 4 days. These alterations in the Cai2+ oscillations triggered by glucose could not be ascribed to desynchronization of the signal between different regions of the islets. In conclusion, culturing normal mouse islets in 5 or 10 mmol/l glucose for 1-4 days, markedly alters the characteristics of the changes in Cai2+ produced by glucose.(ABSTRACT TRUNCATED AT 250 WORDS