Investigation Of A Possible Non-Neuronal Cholinergic System In The Vasculature

HEC Davis, KA Dora, CJ Garland. University of Oxford, Oxford, UK

The localisation of muscarinic receptors on vascular endothelial cells and the consequences of activating these receptors are extensively documented. However, it is not known if endogenous acetylcholine (ACh) is available to activate receptors, and if so, where it originates (1). As acetylcholine, its receptors and synthesising enzymes are widely expressed in extra-neuronal cells and tissues (the non-neuronal cholinergic system) including blood cells (2,3), we investigated a potential role for these cells as a source of endogenous ACh to stimulate the endothelium.

Isolated mesenteric arteries from adult male Wistar rats were cut open and mounted en-face. Endothelial cells were loaded with a calcium indicator dye to measure changes in intracellular calcium using confocal microscopy.

Endothelial cells displayed transient but pronounced increases in the frequency of spontaneous endothelial cell calcium events (1.23 ± 0.15 vs 6.12 ± 0.56 events/min, n=24, P=< 0.0001) and an increase in the number of active cells (23 ± 3 vs 84 ± 4 %, n=24, P=<0.0001) upon exposure to whole blood from rat. ATP was shown not to be an active component of this response by treatment with apyrase (1unit/mL; 6.12 ± 0.63 vs 5.63 ± 0.85 events/min, n=3, P=0.75), however sensitivity to block with atropine (1μμM) was observed (6.79 ± 0.72 vs 4.855 ± 0.64, n=13, P=0.0017).

Taken together these data suggest that endogenous ACh may originate in sufficient quantities from blood cells to stimulate endothelial cell calcium increases. As such this may represent a significant auto or paracrine influence on vascular tone by activating endothelial cell dilator pathways.

(1) Tangsucharit et al. (2012). Am J Physiol Regul Integr Comp Physiol 303: 1147-1156.

(2) Kawashima, K, and Fujii, T. (2008). J Pharmacol Sci 106: 167-173.

(3) Fujii et al. (1995). Neurosci Lett 201: 207-210.