Abstract
Changes in cytosolic free calcium concentration ([Ca 2+] i) in response to stimulatory glucose concentrations were investigated in human pancreatic islets, using Fura-2 fluorescence imaging. Increasing glucose concentration from 3 to 11 mM caused a triphasic [Ca 2+], response in human islets: an initial decrease (phase 1), a rapid and transient increase (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 [Ca 2+] i oscillations to 0.15 ± 0.2 min −1, without changes in their amplitude. Human islet [Ca 2+] i response to stimulatory glucose concentrations is synchronous throughout the islet. Freshly isolated human islets responded to tolbutamide (50 μM with a rise in [Ca 2+] i. An increase in glucose concentration, from 3 to 16 mM, in the presence of 100 μM diazoxide, produced a decrease in [Ca 2+] i It is concluded that human islets respond to glucose with regular [Ca 2+] i oscillations that are synchronous throughout the islet and whose duration is modulated by glucose.
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