Radioligand techniques

CB, was identified by radioligand binding techniques and subsequently cloned. A second receptor subclass, CB2, has been identified in human spleen and also has been cloned (34). Table 5 Hsts cannabinoid receptor ligands. 

Direct quantitation of receptor concentrations and dmg—receptor interactions is possible by a variety of techniques, including fluorescence, nmr, and radioligand binding. The last is particularly versatile and has been appHed both to sophisticated receptor quantitation and to dmg screening and discovery protocols (50,51). The use of high specific activity, frequendy pH]- or p lj-labeled, dmgs bound to cmde or purified cellular materials, to whole cells, or to tissue shces, permits the determination not only of dmg—receptor saturation curves, but also of the receptor number, dmg affinity, and association and dissociation kinetics either direcdy or by competition. Complete theoretical and experimental details are available (50,51). 

There are a number of techniques used for target identification. Radioligand binding was a common technique until recently. Now DNA microarrays, expressed sequence tags, and in silico methods are used. 

Wang, J.-X., Yamamura, H. I., Wang, W, Roeske, W. R. The use of the filtration technique in in vitro radioligand binding assays for membrane-bound and solubilized receptors, in Receptor-Ligand Interactions. A Practical Approach, ed. Hulme, E. C., IRL Press, Oxford,... 

Rahman, A., Choudhary, M. 1., Thomsen, W. J. Radioligand binding assays, in Bioassay Techniques for Drug Development, ed. Rahman, A., Choudhary, M. 1., Thomsen, W. J., Harwood Academic Publishers, Amsterdam, 2001, pp 179-218. 

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