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Pharmacology > 1) Drug Receptors and Ion Channels > Flashcards

1) Drug Receptors and Ion Channels Flashcards

1
Q

Pharmacodynamics

A
  • Actions of a drug on the body

- Influence of drug concentrations on the magnitude of the response

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2
Q

Receptor effects

A
  • Molecules that allow for therapeutic and toxic effects of drugs upon their interaction
  • Responsible for selectivity of drug action
  • Mediate action of agonists/antagonists
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3
Q

Receptors largely determine

A
  • Quantitative relations between dose

- Concentration of drug and pharmacologic effects

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4
Q

Determination of whether and with what affinity a drug will bind to a particular receptor is dependent on

A
  • Molecular size
  • Shape
  • Electrical charge
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5
Q

Dose-response curve example

A
  • 81 mg (dose) Aspirin can cause blood thinning (response) which can be plotted on a graph termed
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6
Q

Affinity of a receptor to a specific molecule will determine

A
  • The concentration needed for this molecule to
    produce a response
  • The interaction between a drug and a receptor is specific
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7
Q

Agonist

A
  • An agent which activates a receptor to produce an effect similar to that of the physiological signal molecule
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8
Q

Antagonist

A
  • An agent which prevents the action of an agonist on a receptor, but does not have any effect of its own
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9
Q

Characteristics of antagonists

A
  • Do NOT activate a signal generation
  • Do NOT produce a reverse signal of the agonist
  • Occupy the receptor
  • Block the ability of an agonist to activate the receptor
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10
Q

Signal transduction

A
  • The binding of drug to its receptor generates signal transduction
  • Elicits a biological response
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11
Q

Second messenger/effector molecules

A
  • Part of the downstream cascade of events that translates agonist binding into a cellular response
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12
Q

Receptors exist in at least two states

A
  • Inactive (R)
  • Active (R*)
  • R and R* are in reversible equilibrium with each other
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13
Q

Binding of agonists causes the equilibrium to shift from R to R* to produce a biologic effect

A

Binding of agonists causes the equilibrium to shift from R to R* to produce a biologic effect

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14
Q

Antagonists occupy the receptor but do not

A
  • Shift the receptor state to R*
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15
Q

Partial agonists shifts receptor state to R, but the fraction of R is

A
  • Less than that caused by an agonist
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16
Q

The magnitude of biological effect is directly related to

A
  • The fraction of R*
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17
Q

The magnitude of the drug effect depends on

A
  • Drug concentration at the receptor site
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18
Q

Drug concentration at the receptor site is determined by

A
  • Dose of drug administered - Drug’s pharmacokinetic profile (such as rate of absorption, distribution, metabolism, and elimination)
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19
Q

As the concentration of a drug increases, its pharmacologic effect

A
  • Also gradually increases until all the receptors are occupied (the maximum effect (Emax))
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20
Q

Plotting the magnitude of response (effect) against increasing doses of a drug (concentration) produces

A
  • A graded dose-response hyperbolic curve
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21
Q

Two important properties of drugs that can be determined by graded dose–response curves

A
  • Potency

- Efficacy

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22
Q

Usually used to determine

potency (EC50)

A
  • The concentration of drug producing 50% of the maximum effect (EC50)
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23
Q

Efficacy

A
  • Magnitude of response a drug causes when it interacts with a receptor
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24
Q

Efficacy is dependent on

A
  • Number of drug–receptor complexes formed (its ability to activate the receptors and cause a cellular response)
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25
Q

Maximal efficacy of a drug (Emax)

A
  • Used to compare the efficacy between different drugs
  • Assumes that all receptors are occupied by the drug, and no increase in response is observed even if a
    higher concentration of drug is administered
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26
Q

Drug affinity refers to

A
  • Chemical forces that cause a substance to bind its receptor
  • Tells how attracted a drug is to its receptors
  • Measures tightness/strength with which a drug binds to the receptor
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27
Q

Kd represents

A
  • Equilibrium dissociation constant for the drug from the receptor
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28
Q

The value of Kd can be used to determine

A
  • Affinity of a drug for its receptor
29
Q

The higher the Kd value

A
  • The weaker the interaction and the lower the affinity, and vice versa
30
Q

Full agonist

A
  • Binds to a receptor and produces maximal biologic response that mimics the
    response to the endogenous ligand
  • All full agonists for a receptor population should produce the same Emax
31
Q

Partial agonists

A
  • Have intrinsic activities greater than zero, but less than the full agonist
  • Even if all the receptors are occupied, partial agonists cannot produce the same Emax as a full agonist
32
Q

Partial agonist affinity

A
  • May be greater, less, or equivalent to a full agonist

- It can bind to the receptor with same affinity as the full agonist, but its pharmacological action is less

33
Q

Spare receptors

A
  • Certain number of receptors that exist in excess of those required to produce a full effect
34
Q

Allosteric site

A
  • Part of receptor other than the active site (usually of the agonist)
  • There are allosteric activator and inhibitors
35
Q

Inverse agonists

A
  • Exert the opposite pharmacological effects of agonists when they bind to the
    receptors
36
Q

Antagonists bind to a receptor with high affinity, but possess zero

A
  • Intrinsic activity
37
Q

An antagonist has no effect in the absence of an

A
  • Agonist

- But it can decrease the effect of an agonist when present

38
Q

Competitive antagonists

A
  • Both the antagonist and agonist bind to the same site on the receptor in a reversible manner
  • Competitive antagonist prevents an agonist from binding to its receptor and maintains the receptor in its
    inactive state
39
Q

Competitive inhibition can be overcome by

A
  • Increasing the concentration of agonist relative to antagonist
40
Q

Competitive antagonists characteristically shift the agonist dose-response curve

A
  • To the right (increased EC50) without affecting Emax
41
Q

Irreversible antagoinsts

A
  • Bind covalently to the same active site of the receptor as the agonist
  • Causes a downward shift of the Emax, with no shift of EC50 values
42
Q

Irreversible antagonists are considered noncompetitive antagonists

A
  • They cannot be displaced by increasing concentration of agonist
43
Q

An antagonist that binds to the active site of a receptor is said to be “non-competitive” if

A
  • The bond between the active site and the antagonist is irreversible or nearly so
44
Q

Non-competitive antagonists reduce

A
  • Agonist efficacy (decrease Emax)
45
Q

Allosteric antagonists are also considered

A
  • Non-competitive antagonists
46
Q

Major classes/types of receptors

A
  • Ligand-gated ion channels,
  • G protein-coupled receptors,
  • Transmembrane enzyme-linked receptors
  • Transmembrane tyrosine kinase receptors
  • Intracellular receptors
47
Q

Intracellular receptors

A
  • Several biologic ligands are sufficiently lipid- soluble to cross the plasma membrane and act on intracellular receptors
  • Example: steroids (corticosteroids), and thyroid hormone
  • Ligand lipophilicity
48
Q

Transmembrane receptor example

A
  • Receptors mediating the signaling of insulin, epidermal growth factor (EGF)
49
Q

Transmembrane receptors consist of

A
  • An extracellular ligand-binding domain, and a cytoplasmic enzyme domain which may be a protein tyrosine kinase
50
Q

Upon binding of EGF, the transmembrane receptor

A
  • Converts from inactive monomeric state (L) –> active dimeric state
    (R), in which two receptor polypeptides bind noncovalently
51
Q

Kinase refers to

A
  • Adding a phosphate atom
52
Q

The cytoplasmic domains of transmembrane receptors (kinases) become

A
  • Phosphorylated on specific tyrosine residues and activated, catalyzing phosphorylation of substrate proteins
53
Q

Ligand binding site is located

A
  • The extracellular portion of ligand-gated ion channels
54
Q

Depending on the ion conducted through these channels, gated channels mediate diverse functions, including

A
  • Neurotransmission

- Cardiac or muscle contraction

55
Q

Two types of gated channels

A
  • Ligand-gated: ion-channels opens to allow passage of ion when ligand binds
  • Voltage-gated: opens when a certain voltage change takes place
56
Q

G-protein coupled receptors

A
  • GTP-binding signal transducer protein

- The extracellular domain of this receptor contains the ligand-binding area

57
Q

When the G-protein coupled receptor is activated by binding to a ligand

A
  • The intracellular domain interact with a G- protein
58
Q

Types of G-proteins

A
  • Gs, Gi and Gq
  • All composed of three protein subunits
  • α subunit binds guanosine triphosphate (GTP)
  • β and γ subunits anchor the G protein in the cell membrane
59
Q

G-protein receptor binding

A
  • Agonist binds to the receptor
  • α subunit binding GTP dissociates from the βγ subunits
  • Sometimes, the activated effectors produce second messengers > activate other effectors > signal cascade effect
60
Q

Adenylyl cyclase

A
  • A common effector
  • Activated by Gs and inhibited by Gi
  • Produces the second
    messenger cyclic adenosine monophosphate (cAMP)
61
Q

G-stimulatory (Gαs)

A
  • Activates adenylyl cyclase
62
Q

G- inhibitory (Gαi)

A
  • Inhibits adenylyl cyclase
63
Q

Gαq

A
  • Activates Phospholipase C
64
Q

Tachyphylaxis

A
  • When a receptor is exposed to repeated administration of an agonist, the receptor becomes desensitized resulting in a diminished effect
  • Diminished response due repeated administration
65
Q

Up-regulation

A
  • Receptors are sequestered within the cell
  • Become unavailable for further agonist interaction
  • These may be recycled to cell surface, restoring sensitivity
66
Q

Down-regulation

A
  • Receptors are sequestered within the cell
  • Become unavailable for further agonist interaction
  • May be further degraded, decreasing the total number of receptors available
67
Q

Repeated exposure of a receptor to an antagonist may result in up-regulation of receptors, in which

A
  • Receptor reserves
    are inserted into the membrane, increasing the total number of receptors available
  • Makes cells more sensitive to agonists
68
Q

Tolerance

A
  • A gradual decreased response to a drug, requiring a higher dose of drug to achieve the same initial response
69
Q

Tolerance versus tachyphylaxis

A
  • Tolerance develops over a long period of time, and can be overcome by increasing dose
  • Tachyphylaxis is an acute event

Pharmacology (27 decks)

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