Binding potential

In pharmacokinetics and receptor–ligand kinetics the binding potential (BP) is a combined measure of the density of "available" neuroreceptors and the affinity of a drug to that neuroreceptor.

In pharmacokinetics and receptor–ligand kinetics the binding potential (BP) is a combined measure of the density of "available" neuroreceptors and the affinity of a drug to that neuroreceptor. BP=\frac{RL}{L}\bigg|_{L\approx0} This quantity, originally defined by Mintun, describes the capacity of a receptor to bind ligand. It is a limit (L RL=\frac{R*L}{L+Ki} and is thus also equivalent to: BP=\frac{R}{K_i} These equations apply equally when measuring the total receptor density or the residual receptor density available after binding to second ligand - availability. BP_2 : The "specific to nonspecific equilibrium partition coefficient", in the literature also denoted as V_3 . This is the ratio of specifically bound to nondisplaceable tracer in brain tissue at true equilibrium. It can be calculated without arterial blood sampling. In the two-tissue compartment model: BP_2=k_3/k_4 and BP_2=f_2BP where f_2 is the free fraction of the tracer in the first tissue compartment, i.e. a measure that depends on the nonspecific binding of the ligand in brain tissue BP_1 : The ratio of specifically bound tracer to tracer in plasma at true equilibrium, in the literature also denoted BP' . Measuring BP_1 includes measurements of radioactivity in plasma, including metabolite correction. From the two-tissue compartment model and by assuming there is only passive diffusion across the blood brain barrier, one obtains: BP_1=f_1BP where f_1 is the free fraction of the tracer in arterial plasma, i.e. a measure that depends on plasma binding. Measuring and dividing by f_1 finally allows to obtain BP. B_{max} : Total density of receptors = R+RL . In PET imaging, the amount of radioligand is usually very small (L B_{max} \approx R k_3 and k_4 : Transfer rate constants from the two tissue compartment model. NEW NOTATIONAL CONVENTIONS: In Innis et al., a large group of researchers who are active in this field agreed to a consensus nomenclature for these terms, with the intent of making the literature in this field more transparent to non-specialists. The convention involves use of the subscripts p for quantities referred to plasma and ND for quantities referred to the free plus nonspecifically bound concentration in brain (NonDisplaceable). Under the consensus nomenclature, the parameters referred to above as f 1 and BP 1 are now called f p and BP p , while f 2 and BP 2 are called f ND and BP ND .

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