Principles of Receptor Binding Assays: The Gaba Receptor
In order to fully exploit the potential of receptor binding assays and to avoid the misinterpretation of data, it is essential to have an understanding of the fundamental principles that govern this procedure. Some important considerations include choice of ligand, isotopic species, tissue preparation and incubation conditions. Thus, the manner in which tissue is stored and prepared, as well as the incubation buffer, temperature, time and method for terminating the assay may all influence binding site selectivity.
For example, by modifying the incubation conditions it has been possible to identify several pharmacologically and kinetically distinct binding sites for y-aminobutyric acid (GABA) in brain tissue. Whereas sodium-independent GABA binding appears to represent attachment to the electrophysiologically relevant recognition site for this substance, the binding detected in the presence of sodium has the characteristics of a transport rather than a recognition site. By modifying the tissue preparation, e.g. by pre-incubating with detergent or extensively washing the membranes, it is possible to identify a second, kinetically distinct, sodium-independent GABA binding site. Moreover, with yet another type of tissue preparation a calcium- dependent GABA recognition site has been detected. Pharmacologically, this membrane constituent is entirely different from the other sodium-independent sites. Furthermore, by using various radioligands it has been possible to identify separate subunits of the GABA receptor complex, such as the chloride channel and benzodiazepine component.
KeywordsBinding Assay Recognition Site Tissue Preparation Gaba Receptor Incubation Condition
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