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 (PKA) 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 PKA 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 PKA activity via activating a Ca(2+)-sensitive adenylyl cyclase 8 (ADCY8) subpool. Glucose stimulation triggered coupled Ca(2+) 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 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.
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 (PKA) 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 PKA 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 PKA activity via activating a Ca(2+)-sensitive adenylyl cyclase 8 (ADCY8) subpool. Glucose stimulation triggered coupled Ca(2+) 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 Ca(2+) influx plays dual roles in regulating exocytosis in ratpancreatic 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.
Authors: Luis R Landa; Mark Harbeck; Kelly Kaihara; Oleg Chepurny; Kajorn Kitiphongspattana; Oliver Graf; Viacheslav O Nikolaev; Martin J Lohse; George G Holz; Michael W Roe Journal: J Biol Chem Date: 2005-06-29 Impact factor: 5.157
Authors: Natalia Gustavsson; Ye Lao; Anton Maximov; Jen-Chieh Chuang; Elena Kostromina; Joyce J Repa; Cai Li; George K Radda; Thomas C Südhof; Weiping Han Journal: Proc Natl Acad Sci U S A Date: 2008-02-28 Impact factor: 11.205
Authors: Brian Tenner; Michael Getz; Brian Ross; Donya Ohadi; Christopher H Bohrer; Eric Greenwald; Sohum Mehta; Jie Xiao; Padmini Rangamani; Jin Zhang Journal: Elife Date: 2020-11-17 Impact factor: 8.140
Authors: Sindhu Rajan; Lorna M Dickson; Elizabeth Mathew; Caitlin M O Orr; Johanne H Ellenbroek; Louis H Philipson; Barton Wicksteed Journal: Mol Metab Date: 2015-02-03 Impact factor: 7.422