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Association Rate Constants as Determinants of Ligand Selectivity:Lessons from The Dopamine And The Serotonin Transporter
Author(s) -
Freissmuth Michael,
Hasenhuetl Peter,
Sucic Sonja,
Sitte Harald,
Sandtner Walter
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.932.1
Subject(s) - dopamine transporter , serotonin transporter , desipramine , serotonin plasma membrane transport proteins , transporter , chemistry , norepinephrine transporter , pharmacology , affinities , dopamine , ligand (biochemistry) , serotonin , methylphenidate , binding site , antidepressant , stereochemistry , biology , endocrinology , psychology , biochemistry , receptor , psychiatry , attention deficit hyperactivity disorder , gene , hippocampus
Cocaine and methylphenidate (MPH) act as competitive inhibitors at the dopamine transporter (DAT). Both drugs bind DAT with similar affinities, but they differ fundamentally with respect to their action on the closely related serotonin transporter (SERT): cocaine inhibits SERT and DAT in a comparable concentration range, but MPH is highly selective for DAT. Conversely, other inhibitors exist, e.g. desipramine, which has a profile opposite to MPH: desipramine blocks SERT with much higher affinity than DAT. The kinetic determinants of this ligand selectivity have remained enigmatic due to methodological limitations. The prevailing view is to ‐ explicitly or implicitly – assume that – by analogy with affinity – selectivity is mainly determined by the dissociation rate of a ligand. We developed an electrophysiological approach to measure the binding of SERT and DAT inhibitors with high temporal precision. The method explored allows for measuring association (k on ) and dissociation rates (k off ) of drugs over a wide affinity range. We exemplify our approach by comparing the rates of cocaine‐, MPH‐ and desipramine‐binding to SERT and DAT. Cocaine has a two‐fold higher affinity for DAT than for SERT, which is accounted for by a twofold slower k off . In contrast the low affinity of MPH for SERT was due to a 20‐fold slower k on than that for binding of MPH to DAT. Conversely, the association of desipramine to SERT occurred at a rate that was 10 times faster than the rate observed for DAT. These findings highlight an important contribution of the forward binding reaction to drug selectivity.