Oscillations of sub-membrane ATP in glucose-stimulated beta cells depend on negative feedback from Ca2+

Abstract

Aims/hypothesisATP links changes in glucose metabolism to electrical activity, Ca2+ signalling and insulin secretion in pancreatic beta cells. There is evidence that beta cell metabolism oscillates, but little is known about ATP dynamics at the plasma membrane, where regulation of ion channels and exocytosis occur.MethodsThe sub-plasma-membrane ATP concentration ([ATP]pm) was recorded in beta cells in intact mouse and human islets using total internal reflection microscopy and the fluorescent reporter Perceval.ResultsGlucose dose-dependently increased [ATP]pm with half-maximal and maximal effects at 5.2 and 9 mmol/l, respectively. Additional elevations of glucose to 11 to 20 mmol/l promoted pronounced [ATP]pm oscillations that were synchronised between neighbouring beta cells. [ATP]pm increased further and the oscillations disappeared when voltage-dependent Ca2+ influx was prevented. In contrast, K+-depolarisation induced prompt lowering of [ATP]pm. Simultaneous recordings of [ATP]pm and the sub-plasma-membrane Ca2+ concentration ([Ca2+]pm) during the early glucose-induced response revealed that the initial [ATP]pm elevation preceded, and was temporarily interrupted by the rise of [Ca2+]pm. During subsequent glucose-induced oscillations, the increases of [Ca2+]pm correlated with lowering of [ATP]pm.Conclusions/interpretationIn beta cells, glucose promotes pronounced oscillations of [ATP]pm, which depend on negative feedback from Ca2+. The bidirectional interplay between these messengers in the sub-membrane space generates the metabolic and ionic oscillations that underlie pulsatile insulin secretion.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-013-2894-0) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Direct Measurements of Oscillatory Glycolysis in Pancreatic Islet β-Cells Using Novel Fluorescence Resonance Energy Transfer (FRET) Biosensors for Pyruvate Kinase M2 Activity

“…Finally, models based on the oscillating activity of the muscle isoform of PFK1, which is present in ␤-cells and possesses the appropriate K d for both the autocatalysis of FBP and inhibition by ATP, can uniquely account for slow oscillations such as those observed here (16,22,49,60).…”

“…22). For example, PFK1 activity could be susceptible to oscillating ATP levels (6), which are generated by plasma membrane ATPases as Ca 2ϩ levels vary (60). Although oscillations in NAD(P)H and O 2 can persist in the absence of downstream electrical oscillations (20,21,52), ruling out Ca 2ϩ as a necessary driver of mitochondrial oscillations, it remains formally possible that mitochondrial oscillations are intrinsic, whereas glycolytic oscillations are under Ca 2ϩ or other secondary control.…”

Glucose promotes its own metabolism by acting on the cell-surface glucose-sensing receptor T1R3

“…Probably because of this, [ATP] i response to glucose is biphasic in MIN6 cells [21] whereas islet β-cells present monophasic increase in [ATP] i [22]. It is an interesting question whether the glucose-sensing receptor signals also modulate the metabolic pathway in islet β-cells.…”

The Interaction of Calcium and Metabolic Oscillations in Pancreatic Beta-cells

“…Furthermore, the ATP oscillations depend on negative feedback from the Ca 2` [ 11]. During the process of glycolysis, there is a positive feedback loop of fructose 1,6-bisphosphate (FBP) on phosphofructokinase (PFK) causing the production of more FBP until fructose 6-phosphate (F6P) is depleted, which causes PFK activity to stop until F6P levels recover.…”