Simulation of cytoskeleton influence on spatial Ca2+ dynamics in neuroendocrine cells

Abstract

The adrenal medulla inside the adrenal glands, which is situated over the kidneys, is composed of chromaffin cells. These cells release vital hormones like epinephrine and norepinephrine in response to stress. Cell depolariza- tion force calcium channel opening which allows external calcium to enter inside the cell; this in turn activates vesi- cles towards release. Once Ca 2+ enters inside the cell, it is heterogeneously distributed in different zones of the cyto- plasm and the F-actin cytoskeletal network seems to play a crucial role in this dynamic behavior [1]. Cytoskeleton is a dynamic supporting structure inside the cell that exhibits a very complex 3-D polygonal shape. It forms walls and empty spaces in the cytosol. In chromaffin cells, we have found that the highest levels of Ca 2+ are found in the interior of cytoskeletal cages (empty spaces), whereas Ca 2+ is low in the cytoskeletal walls. This possibly happens because this structure is acting as a physical barrier. Since cytoskeleton is not a static structure, its complex dynamics would affect the Ca 2+ spatial distribution along time and finally, it would also has an impact on exocytosis. Moreo- ver, we have also encountered evidences that calcium channels are organized in clusters, and that they are posi- tioned in the border of cytoskeletal cages together with secretory vesicles. Then, active sites for secretion (where release occurs) may be placed near empty spaces of cytoskeletal cages probably to allow efficient exocytosi