Glucose-dependent activation, activity, and deactivation of beta cell networks in acute mouse pancreas tissue slices
Many details of glucose-stimulated intracellular calcium changes in beta cells during activation, activity and deactivation, as well as their concentration-dependence, remain to be described. Classical physiological experiments indicated that in islets functional differences between individual cells are largely attenuated, but recent findings suggest considerable intercellular heterogeneity, with some cells possibly coordinating the collective responses. To address the above with an emphasis on heterogeneity and describing the relations between classical physiological and functional network properties, we performed functional multicellular calcium imaging in mouse pancreas tissue slices over a wide range of glucose concentrations. During activation, delays to activation of cells and first responder-any cell delays shortened, and the sizes of simultaneously responding clusters increased with increasing glucose. Exactly the opposite characterized deactivation. The frequency of fast calcium oscillations during activity increased with increasing glucose up to 12 mM glucose, beyond which oscillation duration became longer, resulting in a homogenous increase in active time. In terms of functional connectivity, islets progressed from a very segregated network to a single large functional unit with increasing glucose. A comparison between classical physiological and network parameters revealed that the first-responders during activation had longer active times during plateau and the most active cells during the plateau tended to deactivate later. Cells with the most functional connections tended to activate sooner, have longer active times, and deactivate later. Our findings provide a common ground for recent differing views on beta cell heterogeneity and an important baseline for future studies of stimulus-secretion and intercellular coupling.