Local and regional control of calcium dynamics in the pancreatic islet.

Ca is the key intracellular regulator of insulin secretion, acting in the β-cell as the ultimate trigger for exocytosis. In response to high glucose, ATP-sensitive K channel closure and plasma membrane depolarization engage a sophisticated machinery to drive pulsatile cytosolic Ca changes. Voltage-gated Ca channels, Ca -activated K channels and Na /Ca exchange all play important roles. The use of targeted Ca probes has revealed that during each cytosolic Ca pulse, uptake of Ca by mitochondria, endoplasmic reticulum (ER), secretory granules and lysosomes fine-tune cytosolic Ca dynamics and control organellar function. For example, changes in the expression of the Ca -binding protein Sorcin appear to provide a link between ER Ca levels and ER stress, affecting β-cell function and survival. Across the islet, intercellular communication between highly interconnected "hubs," which act as pacemaker β-cells, and subservient "followers," ensures efficient insulin secretion. Loss of connectivity is seen after the deletion of genes associated with type 2 diabetes (T2D) and follows metabolic and inflammatory insults that characterize this disease. Hubs, which typically comprise ~1%-10% of total β-cells, are repurposed for their specialized role by expression of high glucokinase (Gck) but lower Pdx1 and Nkx6.1 levels. Single cell-omics are poised to provide a deeper understanding of the nature of these cells and of the networks through which they communicate. New insights into the control of both the intra- and intercellular Ca dynamics may thus shed light on T2D pathology and provide novel opportunities for therapy.