Calcium influx activates adenylyl cyclase 8 for sustained insulin secretion in rat pancreatic beta cells.
OBJECTIVE
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
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.
Institute of Molecular Medicine, Peking University, 5 Yiheyuan Road, Beijing, 100871, China.
Haiqiang
H
Dou
Changhe
C
Wang
Xi
X
Wu
Lijun
L
Yao
Xiaoyu
X
Zhang
Sasa
S
Teng
Huadong
H
Xu
Bin
B
Liu
Qihui
Q
Wu
Quanfeng
Q
Zhang
Meiqin
M
Hu
Yeshi
Y
Wang
Li
L
Wang
Yi
Y
Wu
Shujiang
S
Shang
Xinjiang
X
Kang
Lianghong
L
Zheng
Jin
J
Zhang
Matthieu
M
Raoux
Jochen
J
Lang
Qing
Q
Li
Jing
J
Su
Xiao
X
Yu
Liangyi
L
Chen
Zhuan
Z
Zhou
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004195:Disease Models, Animal; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction
D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; C118292:adenylyl cyclase 8; D002118:Calcium