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Lecture 8 of BMED2802 (Robin Allan, 2009) at the University of Sydney.

competitive (reversible), competitive (irreversible) and non-competitive

What are the three types of antagonist?


Occupation is governed by what property of the receptor-drug interaction?


Activation is governed by what property of the receptor-drug interaction?

atropa belladonna

What plant is atropine derived from?

selective muscarinic antagonist

What is atropine?

10^-8 mol/L

At approximately what concentration is atropine active?

pupils dilate, dry mouth, hallucinations

What are the effects of atropine?

dose ratio

What does DR stand for in the antagonist calculations?

how much more is needed in presence of antagonist to get same response

What does DR represent?

log(DR - 1) = log XB - log KB

What is the equation for the Schild plot?


If competitive antagonism, slope of the Schild plot will be...


If competitive antagonism, what will the x-intercept of the Schild plot be?

log xB

What is on the x-axis of the Schild plot?

log(DR - 1)

What is on the y-axis of the Schild plot?

-log xB when DR = 2, or x intercept on Schild plot

What equation is used to calculate pA2?

shifts to right

How does a competitive antagonist change the dose-response curve for an agonist?

it doesn't

How does a competitive antagonist change the maximum response?

define antagonist drug, receptor classification

What purposes is the pA2 widely used for?

independent of it

What relationship does the pA2 have to the agonist?

antagonist and receptor

What does the pA2 depend on?


The negative logarithm to base 10 of the molar concentration to reduce the effect of a dose of agonist to that of half the dose

agonists and antagonists

Partial agonists have properties of both...


An antagonist of muscarinic cholinergic receptors

hexamethonium, decamethonium, tubocurarine

3 antagonists of nicotinic cholinergic receptors


Which nicotinic cholinergic receptors does hexamethonium act on?

neuromuscular junction

Which nicotinic cholinergic receptors do decamethonium and tubocurarine act on?

depolarising block

What is unusual about the action of decamethonium?


An antagonist of histamine H1 receptors


An antagonist of β-adrenoceptors

receptor reserve

The concept that the pool of receptors is larger than needed for full response

Scatchard plot

What plot is used to calculate the total number of binding sites?


The total number of binding sites is known as...


What is on the x-axis of the Scatchard plot?


What is on the y-axis of the Scatchard plot?


What does the slope of the Scatchard plot represent?

Bmax (total binding sites)

What does the x-intercept of the Scatchard plot represent?

radioactive labelling

How do you measure extremely low concentrations as seen in the Scatchard plot?

elicit a response

Antagonists, by themselves, do not...

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