Glucokinase activity controls subpopulations of β-cells that alternately lead islet Ca2+oscillations

Abstract

Ca 2+ -driven oscillations in insulin secretion are crucial for glycemic control. Prior studies, performed with single-plane imaging, suggest that subpopulations of electrically coupled β-cells have privileged roles in leading and coordinating the propagation of Ca 2+ waves. Here, we used 3D light-sheet imaging to analyze the location and Ca 2+ activity of single β-cells within the entire islet at >2 Hz. Network analysis indicates that the most highly synchronized β-cells are located at the islet center and remain geographically stable between oscillations. In contrast, β-cells that initiate the Ca 2+ wave ('leaders') are located at the islet periphery and change their identity over time via rotations in the wave axis. Activators of glucokinase and pyruvate kinase were used to further test the influence of glycolysis on these β-cell subpopulations. Glucokinase activation, which increased oscillation period, reinforced leader cells and stabilized the wave axis. Pyruvate kinase activation, despite increasing oscillation frequency, had no effect on leader cells, indicating the wave origin is patterned by fuel input. The 3D islet β-cell network, which did not respond to either treatment, is insensitive to changes in fuel metabolism. These findings emphasize the stochastic nature of Ca 2+ oscillations and identify a role for glucokinase in spatially patterning 'leader' β-cells.