Modeling analysis of inositol 1,4,5-trisphosphate receptor-mediated ca²⁺ mobilization under the control of glucagon-like peptide-1 in mouse pancreatic β-cells

Glucagon-like peptide-1 (GLP-1) is an intestinally derived blood glucose-lowering hormone that potentiates glucose-stimulated insulin secretion from pancreatic β-cells. The secretagogue action of GLP-1 is explained, at least in part, by its ability to stimulate cAMP production so that cAMP may facilitate the release of Ca²⁺from inositol trisphosphate receptor (IP₃R)-regulated Ca²⁺ stores. However, a quantitative model has yet to be provided that explains the molecular mechanisms and dynamic processes linking GLP-1-stimulated cAMP production to Ca²⁺ mobilization. Here, we performed simulation studies to investigate how GLP-1 alters the abilities of Ca²⁺ and IP₃ to act as coagonists at IP₃R Ca²⁺ release channels. A new dynamic model was constructed based on the Kaftan model, which demonstrates dual steady-state allosteric regulation of the IP₃R by Ca²⁺ and IP₃. Data obtained from β-cells were then analyzed to understand how GLP-1 facilitates IP₃R-mediated Ca²⁺ mobilization when UV flash photolysis is used to uncage Ca²⁺ and IP₃ intracellularly. When the dynamic model for IP₃R activation was incorporated into a minimal cell model, the Ca²⁺ transients and oscillations induced by GLP-1 were successfully reconstructed. Simulation studies indicated that transient and oscillatory responses to GLP-1 were produced by sequential positive and negative feedback regulation due to fast activation and slow inhibition of the IP₃R by Ca²⁺. The slow rate of Ca²⁺ -dependent inhibition was revealed to provide a remarkable contribution to the time course of the decay of cytosolic Ca²⁺ transients. It also served to drive and pace Ca²⁺ oscillations that are significant when evaluating how GLP-1 stimulates insulin secretion.