The biological role of non-neuronal acetylcholine in plants and humans

Acetylcholine, one of the most exemplary neurotransmitters, has been detect ed in bacteria, algae, protozoa, tubellariae and primitive plants, suggesti ng an extremely early appearance in the evolutionary process and a wide exp ression in non-neuronal cells, in plants (Urtica dioica), acetylcholine is involved in the regulation of water resorption and photosynthesis. In human s, acetylcholine and/or the synthesizing enzyme, choline acetyltransferase, have been demonstrated in epithelial (airways, alimentary tract, urogenita l tract, epidermis), mesothelial (pleura, pericardium), endothelial, muscle and immune cells (granulocytes, lymphocytes, macrophages, mast cells). The widespread expression of non-neuronal atetylcholine is accompanied by the ubiquitous expression of cholinesterase and acetylcholine sensitive recepto rs (nicotinic. muscarinic). Both receptor populations interact with more or less all cellular signalling pathways. Thus, non-neuronal acetylcholine ca n be involved in the regulation of basic cell functions like gene expressio n, proliferation, differentiation, cytoskeletal organization, cell-cell con tact (tight and gap junctions, desmosomes), locomotion, migration, ciliary activity, electrical activity, secretion and absorption. Nonneuronal acetyl choline also plays a role in the control of unspecific and specific immune functions. Future experiments should be designed to analyze the cellular ef fects of acetylcholine in greater detail and to illuminate the involvement of the non-neuronal cholinergic system in the pathogenesis of diseases such as acute and chronic inflammation, local and systemic infection, dementia, atherosclerosis, and finally cancer.