Vesicle Motion during Sustained Exocytosis in Chromaffin Cells: Numerical Model Based on Amperometric Measurements

Area of Science:

• Cell Biology
• Neuroscience
• Biophysics

Background:

• Chromaffin cells release catecholamines via exocytosis, involving vesicle docking, priming, and fusion.
• Mechanisms of vesicle transport to active sites at the cell membrane remain incompletely understood.

Purpose of the Study:

• To investigate vesicle motion dynamics in chromaffin cells using a combined simulation and experimental approach.
• To determine if vesicle transport influences catecholamine release patterns.

Main Methods:

• Developed a numerical model combining Langevin simulations of vesicle motion with statistical analysis of vesicle arrival times.
• Performed amperometric experiments on bovine-adrenal chromaffin cells under barium ion (Ba2+) stimulation.
• Analyzed amperometric spike-series using time-rescaling transformation for comparability.

Main Results:

• Release statistics deviated significantly from Poisson processes, with inter-spike times fitting gamma distributions.
• Langevin simulations with a harmonic potential guiding vesicles matched experimental gamma distributions.
• Purely diffusive vesicle motion simulations resulted in Poisson statistics, unlike experimental data.

Conclusions:

• Vesicle transport towards the cell membrane is directed, not purely random.
• This directed motion is reflected in the statistical patterns of catecholamine release observed via amperometry.
• Findings align with previous studies indicating biased vesicle movement beneath plasma membranes.