Simultaneous Arrival of Multiple Agonists: How the Endothelium Senses and Responds

The endothelium is the innermost layer of all blood vessels. It controls numerous cardiovascular functions including vascular contractility, haemostasis, inflammation and the exchange of nutrients and waste products between circulating blood and tissue. To control each cardiovascular function, the endothelium processes and responds to endless streams of information that originate from multiple sources (i.e., blood cells, hormones, neighbouring endothelial cells or underlying smooth muscle cells). Although each endothelial cell has only a limited number of interconnected neighbors (on average six) it is able to decipher and respond to multiple streams of information. To process information, specific cells are primed to detect specific activators and these spatially-distinct populations communicate across the endothelial network to coordinate vascular responses. However, how the endothelium integrates and deciphers information when multiple activators are present simultaneously is not understood. Here, by examining the Ca2+ response in thousands of endothelial cells in intact arteries, we show that the interactions of individual endothelial cells give rise to new behaviours that are absent when cells are examined in isolation. In our study, we examined the Ca²⁺ activity in thousands of endothelial cells in intact rat mesenteric arteries exposed to low concentrations (EC25) of acetylcholine, ATP, or both simultaneously. Our findings reveal that cells which respond to acetylcholine but not ATP (‘acetylcholine-sensitive’), exhibit an enhanced Ca²⁺ response when both activators are present together. The same is true for ‘ATP-sensitive’ cells (i.e., cells that do not respond to acetylcholine, EC25) - the Ca2+ response is augmented when both agonists are present. In addition, the number of neighbours that ‘acetylcholine-sensitive’ or ‘ATP-sensitive’ cells have that respond to either agonist, significantly impacts how the Ca2+ response is altered. Interestingly, the augmented response does not conform to a simple linear summation or average of the acetylcholine/ ATP responses. Instead, a new distinct signal is generated. This suggests that cells perform signaling computations and can combine information from multiple sources. New features that appear in a system and which differ from the expectations of the sum of the components are called ‘emergent properties’. Emergent systems arise from non-linear interactions and create new collective behaviors that make the whole (the endothelium) much greater than the sum of the parts (individual endothelial cells). Our data reveals how communication among neighboring endothelial cells results in emergent behavior across the endothelium, and how this novel behavior plays a significant role in influencing cardiovascular function. British Heart Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.