Calcium influx activates adenylyl cyclase 8 for sustained insulin secretion in rat pancreatic beta cells.

AIMS/HYPOTHESIS:Insulin is a key metabolic regulator in health and diabetes. In pancreatic beta cells, insulin release is regulated by the major second messengers Ca(2+) and cAMP: exocytosis is triggered by Ca(2+) and mediated by the cAMP/protein kinase A signalling pathway. However, the causal link between these two processes in primary beta cells remains undefined. METHODS:Time-resolved confocal imaging of fluorescence resonance energy transfer signals was performed to visualise activity, and combined membrane capacitance recordings were used to monitor insulin secretion from patch-clamped rat beta cells. RESULTS:Membrane depolarisation-induced Ca(2+) influx caused an increase in cytosolic duanyu1529 activity via activating a Ca(2+)-sensitive adenylyl cyclase 8 (ADCY8) subpool. Glucose stimulation triggered coupled Ca(2+) oscillations and duanyu1529 activation. ADCY8 knockdown significantly reduced the level of depolarisation-evoked duanyu1529 activation and impaired replenishment of the readily releasable vesicle pool. Pharmacological inhibition of duanyu1529 by two inhibitors reduced depolarisation-induced duanyu1529 activation to a similar extent and reduced the capacity for sustained vesicle exocytosis and insulin release. CONCLUSIONS/INTERPRETATION:Our findings suggest that depolarisation-induced Ca(2+) influx plays dual roles in regulating exocytosis in rat pancreatic beta cells by triggering vesicle fusion and replenishing the vesicle pool to support sustained insulin release. Therefore, Ca(2+) influx may be important for glucose-stimulated insulin secretion.

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