In vivo release of non‐neuronal acetylcholine from the human skin as measured by dermal microdialysis: effect of botulinum toxin

Acetylcholine is synthesized in the majority of non‐neuronal cells, for example in human skin. In the present experiments, the in vivo release of acetylcholine was measured by dermal microdialysis. Two microdialysis membranes were inserted intradermally at the medial shank of volunteers. Physiological saline containing 1  μ M neostigmine was perfused at a constant rate of 4  μ l min −1 and the effluent was collected in six subsequent 20 min periods. Acetylcholine was measured by high‐pressure liquid chromatography (HPLC) combined with bioreactors and electrochemical detection. Analysis of the effluent by HPLC showed an acetylcholine peak that disappeared, when the analytical column was packed with acetylcholine‐specific esterase, confirming the presence of acetylcholine. In the absence of neostigmine, 71±51 pmol acetylcholine ( n =4) was found during a 120 min period. The amount increased to 183±43 pmol ( n =34), when the perfusion medium contained 1  μ M neostigmine. Injection of 100 MU botulinum toxin subcutaneously blocked sweating completely, but the release of acetylcholine was not affected (botulinum toxin treated skin: 116±70 pmol acetylcholine/120 min; untreated skin: 50±20 pmol; n =4). Quinine (1 m M ), inhibitor of organic cation transporters, and carnitine (0.1 m M ), substrate of the Na + ‐dependent carnitine transporter OCTN2, tended to reduce acetylcholine release (by 40%, not significant). Our experiments demonstrate, for the first time, the in vivo release of non‐neuronal acetylcholine in human skin. Organic cation transporters are not predominantly involved in the release of non‐neuronal acetylcholine from the human skin.British Journal of Pharmacology (2006) 147 , 183–187. doi: 10.1038/sj.bjp.0706451