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Pharm Block 1 > Pharmacodynamics: receptors > Flashcards

Pharmacodynamics: receptors Flashcards

Lecture I and II of pharmdynamics

1
Q

Pharmacodynamic characteristics of a drug include:

A
  1. mechanism of action of a drug
  2. therapeutic uses
  3. adverse or side effects
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2
Q

Pharmacokinetics refers to the mechanisms by which the body handles a drug. Includes:

A
  1. absorption
  2. distribution
  3. metabolism
  4. elimination
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3
Q

Drugs do not create effects, they modify ongoing functions…. In other words, a drug cannot make the body do anything it is not already capable of doing

A

Corollary

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4
Q

The effects of the body of most drugs are a result of

A

interactions between the drug and functional macromolecular components of the organism

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5
Q

Dual function of receptors

A

Binds drugs (or ligands, L) Transduces binding into a response

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6
Q

Some alternatives of drug action other then receptors

A

a) Enzyme inhibitors
b) Inhibitors of transporters
c) Inhibitors of ion channels

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7
Q

Receptors are excellent targets for drugs, because they provide these three things

A

a) Specificity:
b) Selectivity:
c) Sensitivity:

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8
Q

a) Specificity:

A

Only a subset of receptors will be affected by a drug

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9
Q

Only a subset of signal transduction pathways will be affected within a cell

A

b) Selectivity

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10
Q

c) Sensitivity:

A

Effects at receptors are amplified within the cell, therefore, only a small amount of drug is needed

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11
Q

Classification schema

A

a) Pharmacological
b) Biochemical
c) Molecular/Structural

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12
Q

(1) based upon studies of structural features of ligands

2) Used to name receptors (eg muscarinic or nicotinic cholinergic receptors

A

a) Pharmacological (Classification schema)

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13
Q

Based upon transduction mechanism: (eg nicotinic receptor is a ligand-gated ion channel while muscarinic receptor signals through G protein coupled receptors)

A

b) Biochemical (Classification schema)

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14
Q

Families of similar gene products

A

c) Molecular/Structural (Classification schema)

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15
Q

Effect is determined by the relative masses of reactants

A

The law of mass action:

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16
Q

k1 * [L] * [R] =

A

k2

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17
Q
  • [LR] k2/k1 =
A

[L]

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18
Q
  • [R]/[LR] KD =
A

k2/k1 (by definition)

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19
Q

KD is

A

the equilibrium, dissociation constant

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20
Q

Describes the “goodness of fit” between ligand and receptor

A

KD

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21
Q

KD is Proportionally/Inversely related to the affinity of ligand for the receptor

A

Inversely

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22
Q

? = [L] * [R]/[LR]

A

KD

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23
Q

R(T) =

A

[LR] + [R]

24
Q

is the total number of receptors in a cell or tissue (bound and unbound)

A

R(T)

25
Q

[LR] =

A

(R(T) * [L])/ (K(D) + [L])

26
Q

A plot of [L] vs. [LR] results

A

in a rectangular hyperbola

27
Q

At very large values of [L], [LR] is

A

approximately R(T)

28
Q

When [L] = KD, [LR] = R(T)* KD/(KD+KD)

or [LR] =

A

1/2 RT

29
Q

Binding occurs as the result of the formation of _________ between the
ligand and the binding site on the receptor

A

chemical bonds

30
Q

Ionic bonds

a) Receptors have ______

A

charged amino acids

31
Q

Ionic bonds

b) Many ligands are ______

A

weak acids or bases and are charged at physiological pH

32
Q

Ionic bonds are the major determinant of ______

A

k1

33
Q

Hydrogen bonds

a) Hydrogen bound to an electronegative atom (O or N) will have ….

A

a partial positive charge

34
Q

Hydrogen bonds

are stronger/weaker/same as ionic bonds, and require closer/further proximity

A

weaker

closer

35
Q

Van der Waals interactions are:

A

Hydrophobic interactions

36
Q

Greatly strengthen the binding interaction and are the major determinant of k2.

A

Van der Waals interactions

37
Q

Act only at very close distances

A

Van der Waals interactions

38
Q

Effect (E) is ________ to the fraction of the total receptor pool that is occupied by ligand

A

proportional
(a) E/Emax is proportional to [LR]/RT
(Occupancy theory)

39
Q

Maximum effect (Emax) occurs when

A

all of the receptors are occupied

Occupancy theory

40
Q

E = (Emax * C)/

A

(KACT + C)

41
Q

KACT is also called

A

“EC50”

42
Q

Problem with occupancy theory

A

the occupancy theory does not explain the effects of ligands that do not produce a maximal effect; or any effect at all

43
Q

Solution for occupancy theory

A

Effect is proportional to the fraction of occupied receptors AND the intrinsic activity (α) of the ligand

44
Q

E/Emax is proportional to

A

α * (LR/RT)

45
Q

Intrinsic activity is

A

a measure of the ability of the LR

complex to elicit the effect being measured

46
Q

For a full agonist, α =

A

1

47
Q

For an antagonist, α =

A

0

48
Q

For a partial agonist

A

0 < α < 1

49
Q

Intrinsic activity is also called

A

efficacy

50
Q

Is the ratio of the Emax of the ligand of interest to the Emax of a full agonist

A

Intrinsic activity

51
Q

Ligand affinity and ligand intrinsic activity are two different properties. A ligand can have high affinity but

A

low (or no) intrinsic activity.

52
Q

Problem: the occupancy requires that all receptors be occupied in order for the maximal effect to occur; Stephenson demonstrated that tissues have

A

“spare receptors”

53
Q

Together with the normally low affinity of endogenous agonists, the presence of spare receptors allows for

A

high sensitivity without long activation time.

54
Q

Solution to spare receptors

A

the effect is a function of the proportion of occupied receptors; EC50 does not necessarily equal the KD

55
Q

Tissues can have a _______reserve of spare receptors or ______ _______ ________ between receptors and the signal transduction process

A

high

variable coupling efficiency

56
Q

So the function of spare receptors is

A

to increase the sensitivity of the cell to a low concentration of ligand

57
Q

When does EC50 not = Kd

A

when we have spare receptors

Pharm Block 1 (23 decks)

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