What is the pA2 of an antagonist?
pA2. pA2 is a measure of the potency of an antagonist. It is the negative logarithm of the molar concentration of an antagonist that would produce a 2-fold shift in the concentration response curve for an agonist.
What is the pA2 of an antagonist and how would it be evaluated?
The pA2 value indicates the concentration of antagonist when double the agonist is required to have the same effect on the receptor as when no antagonist is present. Multiply the result by negative one.
What does a higher pA2 value mean?
The higher the value for pA2, the higher the affinity of B is to its receptor.
Where is pA2 in Schild plot?
The pA2 is defined as the negative common logarithm of B which produces a dose-ratio of 2; hence, pA2 = -log B = -log KB = 10g(1jKB). Since IjKB is the affinity constant, the pA2 may be viewed as a measure of affinity.
What is pA2 a measure of?
The pA2 is a measure of the affinity of a competitive antagonist for its receptor. The determination of the pA2 is made from experiments in which a fixed concentration of the antagonist is used along with graded concentrations of an agonist acting on the same receptor.
Does pA2 value have units?
pA2 is the negative logarithm of the concentration of antagonist needed to shift the dose response curve by a factor of 2. The units are the negative log of whatever units you used to enter concentrations as column titles on the data table.
How are pA2 and affinity related?
Is papaverine a non competitive antagonist?
Papaverine also shows a competitive antagonism against norepinephrine but a non competitive antagonism against Ca2+.
How are pa2 and affinity related?
How do you find the antagonist affinity?
Antagonist affinity may be estimated in functional studies by measuring the inhibition of the effect of a fixed concentration of agonist and converting the observed IC50 (inflex point of the observed inhibition curve) to a KB (estimated antagonist dissociation constant) with the equation of Cheng and Prusoff (1973).
What type of antagonist is papaverine?
Papaverine is an inhibitor of PDE enzyme leading to increase cGMP in penile tissue. The major disadvantage of papaverine is corporal fibrozis thought to be a result of low acidity. Phentolamine is an α-receptor antagonist that increases blood flow. Systemic hypotension and tachycardia are its major adverse effects.
What is the PA2 of an antagonist drug?
The “antagonist” drug attempts to block the agonist from working. The pA2 value indicates the concentration of antagonist when double the agonist is required to have the same effect on the receptor as when no antagonist is present. Calculate the base-10 logarithm of Kd.
What is the value of PA2 in pharmacology?
The value of pA2 is a negative logarithm of the molar concentration of competitive antagonist, which requires a doubling of the concentration of agonist to compensate for the action of the antagonist. The meaning of pA2 is the affinity of the antagonist to the receptor (4). Similarly, what does KD mean in pharmacology? KD = dissociation CONSTANT.
How are PA2 values used to identify receptors?
However, if the pA2 values of this antagonist differ for each of the agonists, the latter probably act on different receptors. Also, pA2 values can be used to identify receptors in different effectors since effectors with similar receptors would be expected to give the same pA2 for a particular antagonist.
What is the negative logarithm of PA2?
1. 2mportance of pA~ In 1947, Schild introduced the term pA2 as a measure of the strength of a competitive antagonist (1). Specifically, pA2 is the negative logarithm of the molar concentration of the antagonist which produces an agonist dose ratio of 2.