Regular Article

Monte Carlo simulation of the effects of vesicle geometry on calcium microdomains and neurotransmitter release

¹ Biophysics Group, Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
² Department of Bioengineering, University of California, San Diego, CA 92093, USA

^a e-mail: charin.mod@mahidol.edu

Received: 11 June 2015
Revised: 10 January 2016
Accepted: 1 June 2016
Published online: 26 July 2016

Abstract

We investigate the effects of synaptic vesicle geometry on Ca²⁺ diffusion dynamics in presynaptic terminals using MCell, a realistic Monte Carlo algorithm that tracks individual molecules. By modeling the vesicle as a sphere and an oblate or a prolate spheroid with a reflective boundary, we measure the Ca²⁺ concentration at various positions relative to the vesicle. We find that the presence of a vesicle as a diffusion barrier modifies the shape of the [Ca²⁺] microdomain in the vicinity of the vesicle. Ca²⁺ diffusion dynamics also depend on the distance between the vesicle and the voltage-gated calcium channels (VGCCs) and on the shape of the vesicle. The oblate spheroidal vesicle increases the [Ca²⁺] up to six times higher than that in the absence of a vesicle, while the prolate spheroidal vesicle can increase the [Ca²⁺] only 1.4 times. Our results also show that the presence of vesicles that have different geometries can maximally influence the [Ca²⁺] microdomain when the vesicle is located less than 50 nm from VGCCs.