Principles of Pharmacology: Measurement of Drug Action at Receptors

Pharmacology flashcards focusing on radioligand binding, Bmax, Kd, dose-ratio, pA2, and Schild plots.

Radioligand Binding Assay

A technique used to measure the affinity of a drug for a receptor by using a radioactively labeled drug.

Total Binding

The total amount of radioligand bound to a tissue sample, including both specific and non-specific binding.

Non-Specific Binding

The binding of a radioligand to sites other than the specific receptor of interest.

Specific Binding

The binding of a radioligand to the specific receptor of interest, calculated by subtracting non-specific binding from total binding.

Bmax

The maximum number of receptors available for binding in a tissue sample.

Kd (Dissociation Constant)

The concentration of a drug required to occupy 50% of the receptors at equilibrium; a measure of affinity.

Dose-Ratio

The ratio of the concentration of agonist producing the same response in the presence and absence of an antagonist.

pA2

The negative logarithm of the molar concentration of an antagonist that produces a dose ratio of 2; a measure of antagonist affinity.

Schild Plot

A plot of log(dose ratio - 1) versus log antagonist concentration, used to determine if antagonism is competitive and to calculate pA2 and KB.

KB (Equilibrium Dissociation Constant)

Equivalent to KD, but specifically for an antagonist, measured using Schild analysis.

Competitive Antagonist

A drug that binds to the same site as the agonist but does not activate the receptor, and its effects can be overcome by increasing the agonist concentration.

Reversible Antagonist

An antagonist that binds to the receptor non-covalently and can dissociate, allowing the agonist to bind if present in sufficient concentration.

Agonist

A drug that binds to a receptor and activates it, producing a biological response.

Antagonist

A drug that binds to a receptor but does not activate it; it blocks the action of an agonist.

Saturable Binding

Binding that reaches a maximum as all available receptors are occupied.

Log Concentration-Response Curve

A graph plotting the response to a drug against the logarithm of its concentration.

EC50

The concentration of a drug that produces 50% of the maximum possible response.

Schild Analysis

A method used to determine the type of antagonism (e.g., competitive) and to quantify antagonist affinity (pA2).

Parallel Shift

The effect of a competitive antagonist on the agonist log concentration vs response curve; it shifts the curve to the right without changing its shape or maximum.

Affinity

The strength of the binding interaction between a drug and its receptor.