Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, C107

Oral Communications

Multiple Stimuli are Detected by Specialised Cells in the Vascular Endothelium

M. D. Lee1, C. Wilson1, J. G. McCarron1

1. University of Strathclyde, Glasgow, United Kingdom.

The endothelium is the innermost layer of blood vessels and controls virtually all cardiovascular activities. The endothelium uses a multitude of receptors to detect various extracellular agonists. Endless streams of information arrive simultaneously at the endothelium to modulate vascular function. However, it is not yet fully understood how the endothelium can detect multiple simultaneously arriving signals and separately process the information held within each activator. Here, we show the endothelium manages the multitude of extracellular signals by using spatially-distinct endothelial cells that are primed to detect specific extracellular signals. Furthermore, each activator elicits a Ca2+ signal with unique characteristics. When multiple activators are present simultaneously communication occurs between endothelial cells and computations are carried out to generate a new unique Ca2+ signals that are more complex than a simple summation of each signal. To determine how signals evoked by multiple agonists (ACh, ATP, ADP & histamine) were transduced in the endothelium we studied Ca2+ signalling evoked by the agonists in intact arteries. Male Sprague-Dawley rats (150-250g, n=5) were euthanized by CO2 overdose (Schedule 1; Animals (Scientific Procedures) Act 1986) 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. Changes in intracellular Ca2+ in thousands of endothelial cells were measured individually. For each agonist, concentration response curves were carried out to obtain the concentration at which 25% (EC25) of the entire population of endothelial cells were activated. The EC25 concentration of each of the four agonists was applied to the same artery to determine which cells were activated. The Ca2+ signal for each agonist began in spatially-distinct clusters and propagated among cells as Ca2+ waves. There was no significant overlap in the cells that responded to each agonist (P<0.05). Interestingly, the calcium signal for each agonist was unique and the Ca2+ signal was altered when agonists were applied in combination. For example, the Ca2+ signal evoked by ACh had a slow steady increase to a maximum peak were it remained elevated. However, the Ca2+ signal evoked by ATP increased to maximum sharply before falling to baseline level. When both agonists were applied simultaneously the Ca2+ signal was a complex computation of both individual signals. The new Ca2+ signal had a much sharper increase to maximum than ACh alone, but shallower than for ATP. The new Ca2+ signal remained elevated at a much higher level than for ACh alone. These findings show that the endothelium comprises of spatially-distinct populations of cells that are primed to detect specific agonists. These spatially-distinct populations of cells may process the endless streams of information in parallel to control specific cardiovascular functions.

Where applicable, experiments conform with Society ethical requirements