In vivo monitoring of intracellular Ca2+ dynamics in the pancreatic ß-cells of zebrafish embryos.

ABSTRACT

Assessing the response of pancreatic islet cells to glucose stimulation is important for understanding ß-cell function. Zebrafish are a promising model for studies of metabolism in general, including stimulus-secretion coupling in the pancreas. We used transgenic zebrafish embryos expressing a genetically-encoded Ca2+ sensor in pancreatic ß-cells to monitor a key step in glucose induced insulin secretion; the elevations of intracellular [Ca2+]i. In vivo and ex vivo analyses of [Ca2+]i demonstrate that ß-cell responsiveness to glucose is well established in late embryogenesis and that embryonic ß-cells also respond to free fatty acid and amino acid challenges. In vivo imaging of whole embryos further shows that indirect glucose administration, for example by yolk injection, results in a slow and asynchronous induction of ß-cell [Ca2+]i responses, while intravenous glucose injections cause immediate and islet-wide synchronized [Ca2+]i fluctuations. Finally, we demonstrate that embryos with disrupted mutation of the CaV1.2 channel gene cacna1c are hyperglycemic and that this phenotype is associated with glucose-independent [Ca2+]i fluctuation in ß-cells. The data reveal a novel central role of cacna1c in ß-cell specific stimulus-secretion coupling in zebrafish and demonstrate that the novel approach we propose - to monitor the [Ca2+]i dynamics in embryonic ß-cells in vivo - will help to expand the understanding of ß-cell physiological functions in healthy and diseased states.