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What does the term 'Emax' refer to in pharmacodynamics?

The concentration of a drug producing 50% of the maximum effect.

The maximum effect obtainable from a large dose of a drug. (correct)

The amount of drug needed to achieve a specific effect.

The dose that causes death in 50% of subjects.

Which of the following statements correctly describes the therapeutic index (TI)?

It provides information on the efficacy of a drug.

It is determined by the effective concentration of the drug.

A higher TI indicates a greater margin of safety. (correct)

It is the ratio of the average effective dose to the lethal dose.

What characterizes ionotropic receptors?

They typically act on fast neurotransmitters. (correct)

They are slower acting compared to metabotropic receptors.

They are associated with G-proteins.

They work through second messenger systems.

Which subunit is responsible for the catalytic efficiency of G-proteins?

α subunit. Signup and view all the answers

What does EC50 represent in pharmacodynamics?

The effective concentration required to achieve 50% of maximal effect. Signup and view all the answers

Which of these receptors primarily stimulates enzymes or channels?

G-protein coupled receptors. Signup and view all the answers

Which of the following correctly states the function of LD50?

It is the lethal dose that results in death in 50% of test subjects. Signup and view all the answers

How does the action of G-proteins terminate?

Association of the α subunit with the β and γ subunits. Signup and view all the answers

What is the primary action of Gq proteins in cellular signaling?

Activate phospholipase C Signup and view all the answers

Which of the following is a common characteristic of kinase-linked receptors?

Have a large extracellular ligand-binding domain Signup and view all the answers

What type of compounds typically activate nuclear receptors?

Steroid hormones and thyroid hormones Signup and view all the answers

Which of the following mechanisms describes how voltage-gated channels operate?

Open when the membrane is depolarized Signup and view all the answers

Which of the following statements about calcium releasing channels is correct?

They are located on the endoplasmic reticulum membrane. Signup and view all the answers

What effect does cholera toxin have on G-protein signaling?

Activates Gs proteins Signup and view all the answers

What role do nuclear receptors play in cellular function?

Regulate gene expression and protein synthesis Signup and view all the answers

Study Notes

Dose-Response Curve

Plots the response to increasing agonist or antagonist doses.
Measures efficacy (Emax: maximum effect from a large dose) and potency (dose/concentration producing a similar effect to another drug).
EC50: Concentration producing 50% of the maximum effect.
ED50: Dose producing a 50% response in subjects.
LD50: Dose causing death in 50% of subjects.

Therapeutic Index (TI)

Ratio of LD50 to ED50 (TI = LD50/ED50).
Indicates drug safety margin.
Higher TI signifies a safer drug.

Receptor Types

Ligand-Gated Ion Channels (Ionotropic Receptors)

Membrane receptors forming ion channels.
Ligand binding to the extracellular domain opens the channel.
Increases Na+, K+ permeability, potentially generating action potentials.
Fast neurotransmitter receptors (milliseconds).
Examples: Nicotinic acetylcholine receptor, GABA_A receptor.

G-Protein Coupled Receptors (Metabotropic Receptors)

Membrane receptors stimulating enzymes or channels.
Coupled with G-proteins (α, β, γ subunits).
α subunit (GTPase) activates/inactivates enzymes after GTP binding and dissociation.
G-protein classes: G_i, G_s, G_q.
- G_s and G_i regulate adenylate cyclase.
- G_q activates phospholipase C (PLC).
Examples: Cholera toxin (acts on G_s), Pertussis toxin (acts on G_i).
G-protein targets: adenylate cyclase (cAMP), phospholipase C (PLC, IP3, DAG), ion channels (Ca²⁺, K⁺).

Mediate actions of growth factors, cytokines, hormones (e.g., insulin).
Large extracellular (ligand-binding) domain connected to an intracellular (effector) domain.

Nuclear Receptors

Intracellular receptors for steroid hormones, thyroid hormones, vitamin D, retinoic acid, etc.
Ligands (usually lipophilic) cross the cell membrane.
Influence gene expression, protein synthesis, and drug-metabolizing enzymes.
Slowest-acting receptor type.

Other Gating Mechanisms

Voltage-Gated Channels

Open upon membrane depolarization (excitation).
Short-lasting activation.
Examples: Na⁺, K⁺, Ca²⁺ voltage-gated channels.

Calcium-Releasing Channels

Located on endoplasmic reticulum membranes.

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Questions and Answers

What does the term 'Emax' refer to in pharmacodynamics?