GLUCOSE-INDUCED [CA2-ISLETS(](I) OSCILLATIONS IN SINGLE HUMAN PANCREATIC)

Changes in cytosolic free calcium concentration ([Ca2+](i)) in respons e to stimulatory glucose concentrations were investigated in human pan creatic islets, using Fura-2 fluorescence imaging. Increasing glucose concentration from 3 to 11 mM caused a triphasic [Ca2+](i) response in human islets: an initial decrease (phase 1), a rapid and transient in crease (phase 2) and periodic oscillations with a frequency of 1 +/- 0 .3 min(-1) (phase 3). Raising the glucose concentration from 11 to 16. 7 mM lowered the frequency of the glucose-induced [Ca2+](i) oscillatio ns to 0.15 +/- 0.2 min(-1), without changes in their amplitude. Human islet [Ca2+], response to stimulatory glucose concentrations is synchr onous throughout the islet. Freshly isolated human islets responded to tolbutamide (50 mu M) with a rise in [Ca2+](i). An increase in glucos e concentration, from 3 to 16 mM, in the presence of 100 mu M diazoxid e, produced a decrease in [Ca-2+](i). It is concluded that human islet s respond to glucose with regular [Ca2+](i) oscillations that are sync hronous throughout the islet and whose duration is modulated by glucos e.