Correlated oscillations in glucose consumption, oxygen consumption, and intracellular free Ca2+ in single islets of Langerhans

Micron-sized sensors were used to monitor glucose and oxygen levels in the extracellular space of single islets of Langerhans in real-time. At 10 mM g lucose, oscillations in intraislet glucose concentration were readily detec ted. Changes in glucose level correspond to changes in glucose consumption by glycolysis balanced by mass transport into the islet. Oscillations had a period of 3.1 +/- 0.2 min and amplitude of 0.8 +/- 0.1 mM glucose (n = 21) . Superimposed on these oscillations were faster fluctuations in glucose le vel during the periods of low glucose consumption. Oxygen level oscillation s that were out of phase with the glucose oscillations were also detected. Oscillations in both oxygen and glucose consumption were strongly dependent upon extracellular Ca2+ and sensitive to nifedipine. Simultaneous measurem ents of glucose with intracellular Ca2+ ([Ca2+](i)) revealed that decreases in [Ca2+](i) preceded increases in glucose consumption by 7.4 +/- 2.1 a du ring an oscillation (n = 9). Conversely, increases in [Ca2+](i) preceded in creases in oxygen consumption by 1.5 +/- 0.2 s (n = 4). These results sugge st that during oscillations, bursts of glycolysis begin after Ca2+ has stop ped entering the cell. Glycolysis stimulates further Ca2+ entry; which in t urn stimulates increases in respiration. The data during oscillation are in contrast to the time course of events during initial exposure to glucose. Under these conditions, a burst of oxygen consumption precedes the initial rise in [Ca2+](i), A model to explain these results is described.