Radioligands nonspecific binding

FIGURE 5.4 In this illustration of a competition experiment, a fixed concentration of radioligand, in the absence of inhibitor, produces specific binding of B0. The specific binding in the presence of a competitive inhibitor is denoted by Bt A constant amount of nonspecific binding is assumed to be present. The concentration of inhibitor that reduces specific binding by 50% is referred to as the IC50. 

S,R)-p F]Fluoro-CGP 12388 4 was prepared as the less hydrophilic counterpart of the promising non-subtype-selective jS-AR radioligand (S)-[ C]CGP 12388 [97]. PET studies of both, the F- and C-derivative, in male Wistar rats resulted in pulmonary total-to-nonspecific binding ratios of 2.0 for... 

Porcine anterior pituitary membranes were incubated as described in Figure 1 with [3HJspiro-peridol (10-1100 pM). Nonspecific binding was determined in the presence of 1 mM (- -)buta-clamol. Data were analyzed by curve fitting with a model for the binding of the radioligand to one or two classes of sites (14). Data are presented in the Scatchard plot coordinates. The experiment was performed in duplicate and is similar to several other experiments with the same results but it represents an extreme case of the ability of the [3H] antagonist to discriminate between the two forms of the receptor. The two dissociation constants calculated for the control curve are different by about 10-fold. (Reproduced with permission from Ref. 25. 

A method used commonly to estimate the nonspecific binding component involves measuring the amount of radioligand bound in the presence of a large... 

Figure 3 Competition with binding of racemic tribum-labeled WR 171,669 expressed as counts per minute of radioligand bound as function of log of competitor weight (A) or reciprocal of counts per minute of radioligand bound as a funcHon of competitor weight (C). x = binding in absence of compebtor + = nonspecific binding B= d-, A = /, = d,/-WR 171,669. (From Ref. 23, used with permission.)...

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