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 Ca2+ and cAMP: exocytosis is triggered by Ca2+ and mediated by the cAMP/protein kinase A (PKA) signalling pathway. However, the causal link between these two processes in primary beta cells remains undefined.
Results: Membrane depolarisation-induced Ca2+ influx caused an increase in cytosolic PKA activity via activating a Ca2+-sensitive adenylyl cyclase 8 (ADCY8) subpool. Glucose stimulation triggered coupled Ca2+ oscillations and PKA activation. ADCY8 knockdown significantly reduced the level of depolarisation-evoked PKA activation and impaired replenishment of the readily releasable vesicle pool. Pharmacological inhibition of PKA by two inhibitors reduced depolarisation-induced PKA activation to a similar extent and reduced the capacity for sustained vesicle exocytosis and insulin release.
Conclusions/interpretation: Our findings suggest that depolarisation-induced Ca2+ 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, Ca2+ influx may be important for glucose-stimulated insulin secretion.
Methods: Time-resolved confocal imaging of fluorescence resonance energy transfer signals was performed to visualise PKA activity, and combined membrane capacitance recordings were used to monitor insulin secretion from patch-clamped rat beta cells.
- Adenylyl cyclase 8
- Pancreatic beta cell
- Protein kinase A
- Vesicle pool
ASJC Scopus subject areas
- Internal Medicine
- Endocrinology, Diabetes and Metabolism