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The interaction between methylene blue and the cholinergic system
Author(s) -
Pfaffendorf M.,
Bruning T. A.,
Batink H. D.,
Van Zwieten P. A.
Publication year - 1997
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0701355
Subject(s) - acetylcholinesterase , muscarinic acetylcholine receptor , chemistry , acetylcholine , esterase , enzyme , cholinesterase , methylene blue , cholinergic , chromatography , receptor , endocrinology , biochemistry , medicine , biology , photocatalysis , catalysis
1 The inhibitory effects of methylene blue (MB) on different types of cholinesterases and [ 3 H]‐N‐methylscopolamine ([ 3 H]‐NMS) binding to muscarinic receptors were studied. 2 Human plasma from young healthy male volunteers, purified human pseudocholinesterase and purified bovine true acetylcholinesterase were incubated with acetylcholine and increasing concentrations of MB (0.1–100 μmol l −1 ) in the presence of the pH‐indicator m‐nitrophenol for 30 min at 25°C. The amount of acetic acid produced by the enzymatic hydrolysis of acetylcholine was determined photometrically. 3 Rat cardiac left ventricle homogenate was incubated with [ 3 H]‐NMS and with increasing concentrations of MB (0.1 nmol l −1 –100 μmol l −1 ) at 37°C for 20 min. The binding of [ 3 H]‐NMS to the homogenate was quantified by a standard liquid scintillation technique. 4 MB inhibited the esterase activity of human plasma, human pseudocholinesterase and bovine acetylcholinesterase concentration‐dependently with IC 50 values of 1.05±0.05 μmol l −1 , 5.32±0.36 μmol l −1 and 0.42±0.09 μmol l −1 , respectively. MB induced complete inhibition of the esterase activity of human plasma and human pseudocholinesterase, whereas bovine acetylcholinesterase was maximally inhibited by 73±3.3%. 5 MB was able to inhibit specific [ 3 H]‐NMS binding to rat cardiac left ventricle homogenate completely with an IC 50 value of 0.77±0.03 μmol l −1 , which resulted in a K i value for MB of 0.58±0.02 μmol l −1 . 6 In conclusion, MB may be considered as a cholinesterase inhibitor with additional, relevant affinity for muscarinic binding sites at concentrations at which MB is used for investigations into the endothelial system. In our opinion these interactions between MB and the cholinergic system invalidate the use of MB as a tool for the investigation of the L ‐arginine‐NO‐pathway, in particular when muscarinic receptor stimulation is involved.British Journal of Pharmacology (1997) 122 , 95–98; doi: 10.1038/sj.bjp.0701355