ABSTRACT
OBJECTIVE: Computational models of calcium (Ca²âº) signaling have been constructed for several cell types. There are, however, no such models for retinal pigment epithelium (RPE). Our aim was to construct a Ca²âº signaling model for RPE based on our experimental data of mechanically induced Ca²âº wave in the in vitro model of RPE, the ARPE-19 monolayer. METHODS: We combined six essential Ca²âº signaling components into a model: stretch-sensitive Ca²âº channels (SSCCs), P2Y2 receptors, IP3 receptors, ryanodine receptors, Ca²âº pumps, and gap junctions. The cells in our epithelial model are connected to each other to enable transport of signaling molecules. Parameterization was done by tuning the above model components so that the simulated Ca²âº waves reproduced our control experimental data and data where gap junctions were blocked. RESULTS: Our model was able to explain Ca²âº signaling in ARPE-19 cells, and the basic mechanism was found to be as follows: 1) Cells near the stimulus site are likely to conduct Ca²âº through plasma membrane SSCCs and gap junctions conduct the Ca²âº and IP3 between cells further away. 2) Most likely the stimulated cell secretes ligand to the extracellular space where the ligand diffusion mediates the Ca²âº signal so that the ligand concentration decreases with distance. 3) The phosphorylation of the IP3 receptor defines the cell's sensitivity to the extracellular ligand attenuating the Ca²âº signal in the distance. CONCLUSIONS: The developed model was able to simulate an array of experimental data including drug effects. Furthermore, our simulations predict that suramin may interfere ligand binding on P2Y2 receptors or accelerate P2Y2 receptor phosphorylation, which may partially be the reason for Ca²âº wave attenuation by suramin. Being the first RPE Ca²âº signaling model created based on experimental data on ARPE-19 cell line, the model offers a platform for further modeling of native RPE functions.
Subject(s)
Calcium Signaling , Calcium/metabolism , Computer Simulation , Epithelial Cells/metabolism , Models, Biological , Retinal Pigment Epithelium/cytology , Retinal Pigment Epithelium/metabolism , Algorithms , Cell Line , HumansABSTRACT
PURPOSE: The purpose of this study is to develop a computational model of the physical barrier function of the outer blood-retinal barrier (BRB), which is vital for normal retinal function. To our best knowledge no comprehensive models of BRB has been reported. METHODS: The model construction is based on the three-layered structure of the BRB: retinal pigment epithelium (RPE), Bruch's membrane and choriocapillaris endothelium. Their permeabilities were calculated based on the physical theories and experimental material and permeability studies in the literature, which were used to describe diffusional hindrance in specific environments. RESULTS: Our compartmental BRB model predicts permeabilities with magnitudes similar to the experimental values in the literature. However, due to the small number and varying experimental conditions there is a large variability in the available experimental data, rendering validation of the model difficult. The model suggests that the paracellular pathway of the RPE largely defines the total BRB permeability. CONCLUSIONS: Our model is the first BRB model of its level and combines the present knowledge of the BRB barrier function. Furthermore, the model forms a platform for the future model development to be used for the design of new drugs and drug administration systems.
