Veröffentlichungen und Präsentationen

Based on experimental data describing the Ca²⁺ dynamics over a time period of 5 s
in non-stimulated T Cells obtained via high-resolution Ca²⁺ imaging, it was possible to identify the appearance of random spontaneous Ca²⁺ microdomains inside the Endoplasmic Reticulum (ER) - Plasma Membrane (PM) Junctions, which are nano-regions inside the cell cytosol.

We develop a diffusion model using COMSOL Multiphysics® in order to explore the previous results inside a 3D ER-PM junction of 15 nm into the cytosol, where we try to recover numerically the same results as the ones obtained experimentally, at the same time we look to cast some light onto the Ca²⁺ dynamics modulations set by the different channels and pumps involved in the Ca²⁺ uptake processes.

Our model is defined by two united cylindrical domains with a 200 nm diameter. The first domain represents the ER-PM Junction with a 15 nm height to which first Ca²⁺ enters from the extracellular space via five ORAI1 channels opening on a random basis, these sit at the PM (upper boundary surface), then Ca²⁺ will diffuse or be uptake by ten SERCA pumps sitting at the inner boundary with the second domain representing a sub-ER region, where Ca²⁺ will continue to diffuse. The lateral cylindrical surface represents the boundary to the rest of the cytosol. The channels and pumps are placed at the rim of concentric rings at each respective boundary surface.

The physics of our problem is modeled by using the Transport of Diluted Species (tds) physics interface, where we define two different physics configurations for each one of the domains. The dynamics are purely governed by diffusion, therefore we neglect reaction processes. A constant concentration is required at the lateral cylindrical surface and fluxes are only defined along channels and pumps.

We also make use of the Events physics interface to define the random opening/closing of the ORAI1 channels by connecting it to a random function depending on time.

Our preliminary results show that changes on the spatial configuration and number of channels and pumps have a big impact on the temporal evolution and the spatial trace of the Ca²⁺ profile inside the ER-PM Junction domain. The same effects diminish significantly inside the sub-ER.

We are currently performing numerical experiments using different signal configurations in the definition of the random opening/closing of the ORAI1 channels.

We aim at the end to create with the help of the Application Builder an app which can be used by the personnel working at our university labs, that will help them to optimize and improve the experiments preparation and hopefully save time and lab resources.

The mathematical model is based on recent developments done for three-dimensional spatio-temporal modeling of store operated Ca²⁺-entry (SOCE) by [1]

References

[1] . McIvor E, Coobes S, Thul R. Three-dimensional spatio-temporal modelling of store operated Ca2+ entry: Insights into ER refilling and the spatial signature of Ca2+ signals. Cell Calcium. 2018 Apr 04; (73) 11-24.