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Ionic Requirements for the Specific Binding of [ 3 H]GBR 12783 to a Site Associated with the Dopamine Uptake Carrier
Author(s) -
Bonnet J.J.,
Benmansour S.,
Vaugeois J.M.,
Costentin J.
Publication year - 1988
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 - 10.1111/j.1471-4159.1988.tb02979.x
Subject(s) - chemistry , tris , potency , binding site , stereochemistry , choline , membrane , kinetics , sodium , medicinal chemistry , nuclear chemistry , biochemistry , in vitro , organic chemistry , physics , quantum mechanics
At 0°C, when Na + was the only cation present in the incubation medium, increasing the Na + concentration from 3 to 10 m M enhanced the affinity of [ 3 H]l‐[2‐(di‐phenylmethoxy)ethyl]‐4‐(3‐phenyl‐2‐propenyl)piperazine ([ 3 H]GBR 12783) for the specific binding site present in rat striatal membranes without affecting the 5 max . For higher Na + concentrations, specific binding values plateaued and then slightly decreased at 130 m M Na + . In a 10 m M Na + medium, the K D and the B max were, respectively, 0.23 n M and 12.9 pmol/mg of protein. In the presence of 0.4 n M [ 3 H]GBR 12783, the half‐maximal specific binding occurred at 5 m M Na + . A similar Na + dependence was observed at 20°C. Scatchard plots indicated that K + , Ca 2+ , Mg 2+ , and Tris + acted like competitive inhibitors of the specific binding of [ 3 H]GBR 12783. The inhibitory potency of various cations (K + , Ca 2+ , Mg 2+ , Tris + , Li + and choline) was enhanced when the Na + concentration was decreased from 130 to 10 m M . In a 10 m M Na + medium, the rank order of inhibitory potency was Ca 2+ (0.13 m M ) > Mg 2+ > Tris + > K + (15 m M ). The requirement for Na + was rather specific, because none of the other cations acted as a substitute for Na + . No anionic requirement was found: Cl ‐ , Br ‐ , and F ‐ were equipotent. These results suggest that low Na + concentrations are required for maximal binding; higher Na + concentrations protect the specific binding site against the inhibitory effect of other cations.