Newcomer insulin secretory granules as a highly calcium-sensitive pool

Area of Science:

• Endocrinology
• Cell Biology
• Computational Biology

Background:

• Insulin secretion exhibits biphasic kinetics following glucose stimulation.
• Two distinct granule pools, immediately releasable pool (IRP) and highly calcium-sensitive pool (HCSP), have different calcium sensitivities.
• First-phase secretion involves docked granules, while the second phase is attributed to newcomer granules.

Purpose of the Study:

• To extend a computational model of insulin secretion by incorporating the highly calcium-sensitive pool (HCSP).
• To investigate the role of newcomer granules and HCSP in biphasic insulin secretion.
• To explore the interplay between calcium signaling and granule pool depletion in regulating insulin release.

Main Methods:

• Development and application of a mathematical model of exocytosis and insulin release.
• Integration of a highly calcium-sensitive pool (HCSP) into the existing model.
• Validation of the model against experimental data from single cells and glucose-stimulated islets, including genetic knockouts (Ca(2+) channels, Syntaxin-1A).

Main Results:

• The model demonstrates that including the HCSP naturally leads to second-phase insulin secretion predominantly from newcomer granules.
• The model accurately reproduces experimental data from single-cell studies and islet stimulation experiments.
• The model is consistent with data from L- and R-type Ca(2+) channel knockouts and Syntaxin-1A-deficient cells.

Conclusions:

• The HCSP is crucial for sustained, second-phase insulin secretion, primarily utilizing newcomer granules.
• The computational model provides a framework for understanding the mechanisms governing biphasic insulin secretion.
• The study highlights the relative importance of calcium signaling dynamics and granule pool availability in controlling insulin release patterns.