These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: cAMP increases the sensitivity of exocytosis to Ca²+ primarily through protein kinase A in mouse pancreatic beta cells.
    Author: Skelin M, Rupnik M.
    Journal: Cell Calcium; 2011 Feb; 49(2):89-99. PubMed ID: 21242000.
    Abstract:
    Cyclic AMP regulates the late step of Ca²+-dependent exocytosis in many secretory cells through two major mechanisms: a protein kinase A-dependent and a cAMP-GEF/Epac-dependent pathway. We designed a protocol to characterize the role of these two cAMP-dependent pathways on the Ca²+ sensitivity and kinetics of regulated exocytosis in mouse pancreatic beta cells, using a whole-cell patch-clamp based capacitance measurements. A train of depolarizing pulses or slow photo-release of caged Ca²+ were stimuli for the exocytotic activity. In controls, due to exocytosis after slow photo-release, the C(m) change had typically two phases. We observed that the Ca²+-dependency of the rate of the first C(m) change follows saturation kinetics with high cooperativity and half-maximal rate at 2.9±0.2 μM. The intracellular depletion of cAMP did not change amp1, while rate1 and amp2 were strongly reduced. This manipulation pushed the Ca²+-dependency of the exocytotic burst to significantly lower [Ca²+](i). To address the question of which of the cAMP-dependent mechanisms regulates the observed shifts in Ca²+ dependency we included regulators of PKA and Epac2 activity in the pipette solution. PKA activation with 100 μM 6-Phe-cAMP or inhibition with 500 μM Rp-cAMPs in beta cells significantly shifted the EC(50) in the opposite directions. Specific activation of Epac2 did not change Ca²+ sensitivity. Our findings suggest that cAMP modulates Ca²+-dependent exocytosis in mouse beta cells mainly through a PKA-dependent mechanism by sensitizing the insulin releasing machinery to [Ca²+](i); Epac2 may contribute to enhance the rates of secretory vesicle fusion.
    [Abstract] [Full Text] [Related] [New Search]