(Invited) Vesicular Exocytosis in Neuronal and Neuroendocrine Cells: Quantifying Fusion Pore Size from Amperometric Data
Authors: Oleinick Alexander , Svir Irina , Amatore Christian Andre 
Published: February 2020

It is well-known that amperometric measurements of vesicular exocytosis in artificial synapse configuration [1] provide two important advantages: unsurpassed temporal resolution of single exocytotic events and possibility to obtain massive data. These two advantages allow statistical analysis of exocytosis and its trends in different cell types and/or under various physico-chemical conditions (osmotic shocks, effect of drugs etc.). However, generally statistical analysis is restricted to the examination of some shape features of the individual spikes (half-time, charge released etc.) even though all relevant physico-chemical parameters are intricately convoluted in the monitored current. Extraction of these thought parameters is extremely difficult due to the fact that each exocytotic event is unique in terms of vesicle size, its internal composition, neurotransmitter load etc. During several last years we developed a theoretical framework providing means to extract statistically sound fusion pore sizes as well as pore dynamics from individual exocytotic spikes [2-4], that is information hardly accessible or not accessible by other approaches. This permits us to analyze and quantify vesicle pore sizes from amperometric data obtained at chromaffin cells [4] and rat neuro-muscular junctions [5].
Recently we dramatically simplified the fusion pore size extraction procedure (without sacrificing its accuracy) so that it can be easily implemented by the experimentalists, e.g. in spreadsheet programs. This advance allow us to address a larger data set of spikes obtained at chromaffin cells and reveal changes in fusion pores topology under modified conditions (osmotic stress, membrane lipid modification) with respect to control conditions. Of high interest was the finding that in all considered cases the fusion pore radii was never larger 30 nm, that is much smaller to the average radius of the chromaffin cell vesicle 156 nm. Taking into account significant size of the data set (more than 1000 spikes) this questions the ‘inevitable full fusion’ paradigm and statistically support a mode of exocytosis where the pore size is significantly smaller the vesicle size [6].
References:
[1] T.J. Schroeder, J.A. Jankowski, K.T. Kawagoe, R.M. Wightman, C. Lefrou, C. Amatore. Analysis of diffusional broadening of vesicular packets of catecholamines released frombiological cells during exocytosis. Anal. Chem. 64, 1992, 3077–3083.
[2] C. Amatore, A. Oleinick, I. Svir. Diffusion from within a spherical body with partially blocked surface: diffusion through a constant surface area. ChemPhysChem 11, 2010, 149-158.
[3] C. Amatore, A. Oleinick, I. Svir. Reconstruction of aperture functions during full fusion in vesicular exocytosis of neurotransmitters. ChemPhysChem 11, 2010, 159-174.
[4] A. Oleinick, F. Lemaître, M. Guille Collignon, I. Svir, C. Amatore. Vesicular release of neurotransmitters: converting amperometric measurements into size, dynamics and energetics of initial fusion pores. Faraday Discuss. 164, 2013, 33-55.
[5] Y.-T. Li, S.-H. Zhang, X.-Y. Wang, X.-W. Zhang, A.I. Oleinick, I. Svir, C. Amatore, W.-H. Huang. Real-time monitoring of discrete synaptic release events and excitatory potentials within self-reconstructed neuro-muscular junctions. Angew. Chemie 54, 2015, 9313-9318.
[6] A. Oleinick, I. Svir, C. Amatore. “Full Fusion” is not Ineluctable during Vesicular Exocytosis of Neurotransmitters by Endocrine Cells. Proc. Roy. Soc. A, 473, 2017, 20160684.