The non-neuronal cholinergic system in the endothelium: Evidence and possible pathobiological significance

An increasing body of knowledge indicates that the cholinergic system is no t confined to the nervous system, but is practically ubiquitous. The presen t paper will address the question of the non-neuronal cholinergic system in vascular endothelial cells (EC). Ln tissue sections of human skin, immunoh istochemical studies using confocal laser scanning microscopy showed ChAT ( choline acetyltransferase) activity in the EC of dermal blood vessels. Posi tive ChAT immunoreactivity was also demonstrated in manolayer cultures of h uman umbilical vein EC (HUVEC) and a human angiosarcoma EC line (HAEND). Th at the synthesizing enzyme is not only present in EC, but also active was s hown by measuring ChAT activity. Thus, in HUVEC cultures, ChAT activity amo unted to 0.78 +/- 0.15 nmol mg protein(-1).h(-1) (n = 3), but was only part ially (about 50%) inhibited by the ChAT inhibitor bromoacetylcholine (30 mu M). In HPLC measurements, a concentration of 22 +/- 2 pmol acetylcholine (A Ch) per 10(6) cells was found (n = 6). However, using a cholinesterase-pack ed analytical column to check the identity of the acetylcholine peak, the p eak height was found to be reduced, although a significant peak still remai ned, indicating the existence of a compound closely related to ACh. Further immunocytochemical experiments indicated that EC in vitro also express the vesicular acetylcholine transporter (VAChT) system. Preliminary immunoelec tron microscopic studies suggest a topographical association of VAChT with endothelial endocytotic vesicles. The presented experiments clearly demonst rate the existence of essential elements of the cholinergic system (ChAT, V AChT, ACh) in the human endothelium. The biological functions of ACh synthe sized by endothelial cells are the focus of ongoing research activity.