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

Abstract

Aims/hypothesis ATP 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. Methods The 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. Results Glucose 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/interpretation In 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.