A sequential vesicle pool model with a single release sensor and a Ca(2+)-dependent priming catalyst effectively...

Area of Science:

• Neuroscience
• Cell Biology
• Biophysics

Background:

• Neurotransmitter release involves vesicle fusion, with calcium ions (Ca2+) playing a critical role in regulating this process.
• While synaptotagmin-1 is the primary Ca2+ sensor for fast release, slower Ca2+-dependent release components persist even after its deletion, suggesting alternative mechanisms.
• Existing Parallel Pool Models (PPM) propose separate, slowly releasable vesicle pools, but lack identified Ca2+ sensors for these pools.

Purpose of the Study:

• To propose and validate a novel Sequential Pool Model (SPM) for neurotransmitter release.
• To investigate the role of a Ca2+-dependent catalyst in regulating vesicle priming reactions.
• To explain the origins of slow Ca2+-dependent release components and reconcile experimental data with theoretical models.

Main Methods:

• Developed a Sequential Pool Model (SPM) incorporating a Ca2+-dependent catalyst for priming reactions.
• Utilized numerical integration to compare SPM predictions with experimental data from mouse chromaffin cells.
• Analyzed data from synaptotagmin-1 knockout and SNARE-complex mutations to test model validity.

Main Results:

• The SPM successfully explains biphasic release, Ca2+ dependence, and pool sizes in mouse chromaffin cells, similar to PPM.
• Unlike PPM, the SPM accurately accounts for rapid recovery of fast release after intense stimulation.
• The SPM explains simultaneous changes in release rate and amplitude upon SNARE-complex mutation and loss of fast release in synaptotagmin-1 knockouts.

Conclusions:

• The proposed Sequential Pool Model (SPM) offers a viable alternative to Parallel Pool Models (PPM) for explaining Ca2+-dependent neurotransmitter secretion.
• A Ca2+-dependent priming catalyst may act as the elusive 'alternative Ca2+ sensor' for slow release.
• The SPM effectively explains secretion dynamics without necessitating parallel pools or unidentified sensors.