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IIIIIIInteraction of Na + , K + , and Cl ‐ with the Binding of Amphetamine, Octopamine, and Tyramine to the Human Dopamine Transporter
Author(s) -
Li LLLLLLLiBin,
Reith Maarten E. A.
Publication year - 2000
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2000.0741538.x
Subject(s) - dopamine plasma membrane transport proteins , chemistry , octopamine (neurotransmitter) , tyramine , dopamine transporter , binding site , substrate (aquarium) , dopamine , tropane , amphetamine , affinities , stereochemistry , transporter , biophysics , biochemistry , receptor , biology , endocrinology , ecology , serotonin , gene
Little information is available on the role ofNa + , K + , and Cl ‐ in the initial event ofuptake of substrates by the dopamine transporter, i.e., the recognition step.In this study, substrate recognition was studied via the inhibition of bindingof [ 3 H]WIN 35,428[2β‐carbomethoxy‐3β‐(4‐fluorophenyl)[ 3 H]tropane], acocaine analogue, to the human dopamine transporter in human embryonic kidney293 cells. D‐Amphetamine was the most potent inhibitor, followed by p ‐tyramine and, finally, dl ‐octopamine; respectiveaffinities at 150 m M Na + and 140 m M Cl ‐ were 5.5, 26, and 220 μ M . For each substrate, thedecrease in the affinity with increasing [K + ] could be fitted to acompetitive model involving the same inhibitory cation site (site 1)overlapping with the substrate domain as reported by us previously fordopamine. K + binds to this site with an apparent affinity, averagedacross substrates, of 9, 24, 66, 99, and 134 m M at 2, 10, 60, 150,and 300 m M Na + , respectively. In general, increasing[Na + ] attenuated the inhibitory effect of K + in a mannerthat deviated from linearity, which could be modeled by a distal site forNa + , linked to site 1 by negative allosterism. The presence ofCl ‐ did not affect the binding of K + to site 1. Modelsassuming low binding of substrate in the absence of Na + did notprovide fits as good as models in which substrate binds in the absence ofNa + with appreciable affinity. The binding of dl ‐octopamine and p ‐tyramine was strongly inhibited byNa + , and stimulated by Cl ‐ only at high [Na + ](300 m M ), consonant with a stimulatory action of Cl ‐ occurring through Na + disinhibition.