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

Abstract

1 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. 2 Two microdialysis membranes were inserted intradermally at the medial shank of volunteers. Physiological saline containing 1 μM neostigmine was perfused at a constant rate of 4 μl 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. 3 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. 4 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 μM neostigmine. 5 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). 6 Quinine (1 mM), inhibitor of organic cation transporters, and carnitine (0.1 mM), substrate of the Na +-dependent carnitine transporter OCTN2, tended to reduce acetylcholine release (by 40%, not significant). 7 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. © 2006 Nature Publishing Group All rights reserved.