FLUORESCENCE DIGITAL IMAGE-ANALYSIS OF GLUCOSE-INDUCED [CA2-ISLETS OFLANGERHANS(](I) OSCILLATIONS IN MOUSE PANCREATIC)

At intermediate glucose concentrations, [Ca2+]i (intracellular calcium ) measured in single islets of Langerhans undergo oscillations that ar e caused by glucose-induced bursting of electrical activity. Using dig ital video imaging of fura-2-loaded islets, we have analyzed the spati al distribution of [Ca2+]i in response to the natural secretagogue glu cose and the K(ATP) channel blocker tolbutamide. When the glucose leve l is increased, [Ca2+]i first increases and then starts to oscillate w ith a synchronous pattern through the islet. The synchrony is maintain ed even during nonrhythmic oscillatory patterns. In the presence of to lbutamide, [Ca2+]i increases in all the islet regions, suggesting that the calcium signal is derived mainly from the beta-cell population. T hese results demonstrate that the islets behave as a functional syncyt ium in response to stimulatory glucose levels, canceling out heterogen eities at the single cell level.