[Abstract Title]. - Society for Neuroscience

Topic: B.06.a. Docking and fusion
Support: Heart and Stroke Foundation of Canada.
National Science and Engineering Council of Canada
Title: Simulation of vesicular mobility in secretory cells
Authors: *M. I. GLAVINOVIC 1 , M. TAJPARAST 2 ;
1 Dept Physiol, 2 Chem. Engin., McGill Univ., Montreal, QC, Canada
Abstract: Vesicular size is known to be variable and vesicular location changes during secretion.
Vesicular mobility has also been estimated and may change during stimulation. Several forces
are expected to be important in determining the mobility of vesicles in secretory cells: a)
cytoskeleton, b) viscosity of intracellular fluid and c) vesicular size. However, the electrostatic
interactions caused by the surface charges at both vesicular and plasma membranes may also
make a contribution. The vesicular mobility may thus also be influenced by the charge density on
the vesicular and plasma membranes. To assess the importance of various forces in determining
vesicular mobility and to gain better understanding of the dynamics of vesicular movement
during secretion we consider the vesicle in the secretory cell as a nano-size electromechanical
device operating in a liquid electrolyte. We simulate the vesicle as a charged sphere near a
charged dielectric sheet (representing plasma membrane of a secretory cell) using a coupled
system of Poisson-Nernst-Planck and Navier-Stokes equations. The external force acting on the
vesicle is assumed to change in a step-like manner. Several parameters were varied from one
simulation run to another - vesicular radius, vesicular distance from the plasma membrane,
charge density and sign on both membranes, fluid viscosity, concentration of charged particles in
the solution and their diffusion constants. Vesicular „impulse response‟ was determined from the
movement of the vesicle following a step-like change of the external force. Vesicular „impulse
response‟ and mobility are found to be dependent not only on the vesicular size and fluid
viscosity but also on the distance between the vesicle and the plasma membrane, the charge on
both the vesicle and plasma membrane as well as on the concentration of free charged particles
(ions, transmitter, hormones,�). Moreover, an estimate is made of the external force needed to
move the vesicle at speeds as measured experimentally. Finally, for each set of parameters
characterizing the secretory cell and the vesicle, a distance is determined at which the external
force pushing the vesicle toward the plasma membrane is balanced by the repulsive electrostatic
forces.
Disclosures: M.I. Glavinovic , None; M. Tajparast, None.
Poster
236. Neurotransmitter Release: Docking and Fusion