Timing of Ca2+ response in pancreatic β-cells is related to mitochondrial mass

The timing and magnitude of calcium response are cell-specific in individual β-cells. This may indicate that the cells have different roles in the intact islet. It is unknown what mechanisms determine these characteristics. We previously found that the mechanisms setting cell-specific response timing are disturbed in β-cells from hyperglycemic mice and one of the causes is likely to be an altered mitochondrial metabolism. Mitochondria play a key role in the control of nutrient-induced insulin secretion. Here, we used confocal microscopy with the fluorescent probe MitoTracker Red CMXRos and Fluo-3 to study how the amount of active mitochondria is related to the lag-time and the magnitude of calcium response to 20 mM glucose in isolated β-cells and in cells within intact lean and ob/ob mouse islets. Results show that the mitochondrial mass is inversely correlated with the lag-times for calcium response both in lean and ob/ob mouse β-cells (r = −0.73 and r = −0.43, respectively, P < 0.05). Thus, the state of mitochondria may determine the timing of calcium response.