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Ion and Temperature Effects on the Binding of γ ‐Aminobutyrate to Its Receptors and the High‐Affinity Transport System
Author(s) -
Shank R. P.,
Baldy W. J.,
Mattucci L. C.,
Villani F. J.
Publication year - 1990
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.1471-4159.1990.tb04905.x
Subject(s) - receptor , gabaa receptor , cooperativity , binding site , gabab receptor , biophysics , gaba receptor , chemistry , cooperative binding , allosteric regulation , biochemistry , biology
A set of procedures was developed to study the binding of γ ‐[ 3 ]‐aminobutyric acid ([ 3 H]GABA) to GABA A and GABA B receptors, and to the Na + ‐dependent transport carrier, at 25 and 37°C in the presence of physiological concentrations of Na + . The membrane preparation used in these procedures was not subjected to freeze–thawing or treatment with Triton X‐100. Isoguvacine, (–)‐baclofen, and (–)‐nipecotate were used to block selectively the binding to GABA A receptors, GABA B receptors, and the transport site, respectively. Analysis of the binding characteristics of [ 3 H]GABA to the GABA A receptor suggested the existence of high‐ ( K D < 30 n M ), middle‐ ( K D 100–500 n M ), and low‐affinity ( K D > 5 μM ) binding sites. However, the binding data in the middle‐affinity region (100–1,000 n M ) were often indicative of cooperativity. The affinity between GABA and the GABA A receptor was reduced modestly by increases in temperature and by the presence of Cl − at physiological concentrations. Binding to the GABA B receptor required Ca 2+ and Cl − . Apparent binding to the transport carrier required both Na + and Cl − . A comparison of B max values in three brain regions revealed an inverse relationship between the high‐affinity site of the GABA A receptor and the transport binding site.