Endothelial Heterogeneity Enables Parallel Processing of Multiple Stimuli
Authors: Lee Matthew D , Wilson Calum , McCarron John G 
Published: April 2020

The endothelium is the innermost layer of all blood vessels and changes in the behavior of this single layer of cells underlie almost all cardiovascular disease. To regulate cardiovascular function, the endothelium must integrate hundreds of signals. These signals can arrive from as close as neighboring cells to substances circulating in the blood from the most remote outpost of the body. However, how the endothelium detects and relays the information stored in each of these signals to initiate a physiological output is not fully understood. The problem in integrating signals is made even more complex as the central relay system within an endothelial cell is a single ion, Ca2+. Here, we show the endothelium manages a multitude of extracellular signals by utilizing spatially‐distinct endothelial cells. Furthermore, the Ca2+ signal generate by each activator has unique distinguishing characteristics.To determine how multiple extracellular signals are detected in the endothelium we analysed the Ca2+ activity from ~1000 endothelial cells from intact arteries. Male‐Sprague‐Dawley rats were euthanized by CO2 overdose and second order mesenteric arteries were extracted, cut open and pinned flat. The endothelium was loaded with a Ca2+ indicator Cal‐520/AM and imaged using fluorescence microscopy. Ca2+ activity was separately analysed in each of the 1000 individual endothelial cells using a custom built software package written in Python.For each activator (ACh, ATP, ADP & Histamine) full concentration response curves were carried out to determine the EC25 concentration (the concentration at which 25% of cells responded). The addition of the four activators (each separately applied), at their respective EC25 concentration, to the same field of endothelium revealed the endothelium utilizes sub‐populations of endothelial cells to detect each activator. The Ca2+ signal began in small sub‐populations of endothelial cells that were organised in clusters and propagated between cells as Ca2+ waves. The cells responsible for the detection of a specific activator were spatially unique and there was no significant overlap with cells that were primed to detect another agonist (P<0.05). Each activator generated a unique Ca2+ signal that was specific to the agonist. When the activators were applied in combination at the EC25 concentration, the unique characteristics of the Ca2+ signal for a specific activator when applied alone was drastically altered. Interestingly, the characteristics of the Ca2+ signal when applied in combination was not a simple linear summation of the individual signals. Expansive responses occurred, in that the outputs exceeded the sum of the inputs. These results suggest individual endothelial cells communicate with their neighbors and complex computations are carried out by combining the information from each source to generate a distinct output. By using spatially‐distinct cells, unique signal characteristics and communication, the endothelium is able to detect and relay the information stored in the multitude of extracellular activators to initiate physiological outputs.Support or Funding InformationWellcome Trust & British Heart FoundationThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.