Epac2-dependent mobilization of intracellular Ca²+ by glucagon-like peptide-1 receptor agonist exendin-4 is disrupted in β-cells of phospholipase C-ε knockout mice

J Physiol. 2010 Dec 15;588(Pt 24):4871-89. doi: 10.1113/jphysiol.2010.198424. Epub 2010 Nov 1.


Calcium can be mobilized in pancreatic β-cells via a mechanism of Ca(2+)-induced Ca(2+) release (CICR), and cAMP-elevating agents such as exendin-4 facilitate CICR in β-cells by activating both protein kinase A and Epac2. Here we provide the first report that a novel phosphoinositide-specific phospholipase C- (PLC-) is expressed in the islets of Langerhans, and that the knockout (KO) of PLC- gene expression in mice disrupts the action of exendin-4 to facilitate CICR in the β-cells of these mice. Thus, in the present study, in which wild-type (WT) C57BL/6 mouse β-cells were loaded with the photolabile Ca(2+) chelator NP-EGTA, the UV flash photolysis-catalysed uncaging of Ca(2+) generated CICR in only 9% of the β-cells tested, whereas CICR was generated in 82% of the β-cells pretreated with exendin-4. This action of exendin-4 to facilitate CICR was reproduced by cAMP analogues that activate protein kinase A (6-Bnz-cAMP-AM) or Epac2 (8-pCPT-2'-O-Me-cAMP-AM) selectively. However, in β-cells of PLC- KO mice, and also Epac2 KO mice, these test substances exhibited differential efficacies in the CICR assay such that exendin-4 was partly effective, 6-Bnz-cAMP-AM was fully effective, and 8-pCPT-2'-O-Me-cAMP-AM was without significant effect. Importantly, transduction of PLC- KO β-cells with recombinant PLC- rescued the action of 8-pCPT-2'-O-Me-cAMP-AM to facilitate CICR, whereas a K2150E PLC- with a mutated Ras association (RA) domain, or a H1640L PLC- that is catalytically dead, were both ineffective. Since 8-pCPT-2'-O-Me-cAMP-AM failed to facilitate CICR in WT β-cells transduced with a GTPase activating protein (RapGAP) that downregulates Rap activity, the available evidence indicates that a signal transduction 'module' comprised of Epac2, Rap and PLC- exists in β-cells, and that the activities of Epac2 and PLC- are key determinants of CICR in this cell type.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calcium Signaling / drug effects
  • Calcium Signaling / physiology
  • Cells, Cultured
  • Cyclic AMP / analogs & derivatives
  • Cyclic AMP / pharmacology
  • Exenatide
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • Gene Expression Regulation / drug effects
  • Glucagon-Like Peptide-1 Receptor
  • Guanine Nucleotide Exchange Factors / genetics
  • Guanine Nucleotide Exchange Factors / metabolism*
  • Insulin-Secreting Cells / drug effects*
  • Insulin-Secreting Cells / metabolism
  • Mice
  • Mice, Knockout
  • Peptides / pharmacology*
  • Phosphoinositide Phospholipase C / genetics
  • Phosphoinositide Phospholipase C / metabolism*
  • Receptors, Glucagon / agonists*
  • Thapsigargin / pharmacology
  • Venoms / pharmacology*


  • 8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate
  • Glp1r protein, mouse
  • Glucagon-Like Peptide-1 Receptor
  • Guanine Nucleotide Exchange Factors
  • Peptides
  • Rapgef4 protein, mouse
  • Receptors, Glucagon
  • Venoms
  • Thapsigargin
  • Exenatide
  • Cyclic AMP
  • Phosphoinositide Phospholipase C
  • Plch1 protein, mouse
  • GTP Phosphohydrolases
  • Calcium