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Methylene blue inhibits function of the 5‐HT transporter
Author(s) -
Oz Murat,
Isaev Dmytro,
Lorke Dietrich E,
Hasan Muhammed,
Petroianu Georg,
Shippenberg Toni S
Publication year - 2012
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 - 10.1111/j.1476-5381.2011.01462.x
Subject(s) - extracellular , serotonin transporter , intracellular , methylene blue , serotonin plasma membrane transport proteins , chemistry , pharmacology , radioligand , transporter , serotonin , biophysics , biology , biochemistry , binding site , receptor , photocatalysis , catalysis , gene
BACKGROUND AND PURPOSE Methylene blue (MB) is commonly employed as a treatment for methaemoglobinaemia, malaria and vasoplegic shock. An increasing number of studies indicate that MB can cause 5‐HT toxicity when administered with a 5‐HT reuptake inhibitor. MB is a potent inhibitor of monoamine oxidases, but other targets that may contribute to MB toxicity have not been identified. Given the role of the 5‐HT transporter (SERT) in the regulation of extracellular 5‐HT concentrations, the present study aimed to characterize the effect of MB on SERT. EXPERIMENTAL APPROACH Live cell imaging, in conjunction with the fluorescent SERT substrate 4‐(4‐(dimethylamino)‐styryl)‐ N ‐methylpyridinium (ASP + ), [ 3 H]5‐HT uptake and whole‐cell patch‐clamp techniques were employed to examine the effects of MB on SERT function. KEY RESULTS In EM4 cells expressing GFP‐tagged human SERT (hSERT), MB concentration‐dependently inhibited ASP + accumulation (IC 50 : 1.4 ± 0.3 µM). A similar effect was observed in N2A cells. Uptake of [ 3 H]5‐HT was decreased by MB pretreatment. Furthermore, patch‐clamp studies in hSERT expressing cells indicated that MB significantly inhibited 5‐HT‐evoked ion currents. Pretreatment with 8‐Br‐cGMP did not alter the inhibitory effect of MB on hSERT activity, and intracellular Ca 2+ levels remained unchanged during MB application. Further experiments revealed that ASP + binding to cell surface hSERT was reduced after MB treatment. In whole‐cell radioligand experiments, exposure to MB (10 µM; 10 min) did not alter surface binding of the SERT ligand [ 125 I]RTI‐55. CONCLUSIONS AND IMPLICATIONS MB modulated SERT function and suggested that SERT may be an additional target upon which MB acts to produce 5‐HT toxicity.