Understanding ion channel receptors is essential for B.Pharm students because these membrane proteins control ionic flux, neuronal excitability, synaptic transmission and are major drug targets. This topic covers ligand-gated and voltage-gated ion channels, ion selectivity, gating mechanisms, kinetics, modulation by drugs (agonists, antagonists, allosteric modulators), channelopathies, and experimental techniques such as patch-clamp. Emphasis is placed on therapeutically relevant channels—nicotinic acetylcholine receptors, GABA-A, NMDA, voltage-gated sodium and calcium channels—and on pharmacological agents like local anesthetics, benzodiazepines, calcium channel blockers and NMDA antagonists. Mastery of these concepts helps in rational drug design, clinical pharmacology and safe medication use. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What defines an ion channel receptor?
- A membrane protein that allows passive ion flow across the membrane when gated
- An enzyme that actively transports ions using ATP
- A nuclear receptor that regulates ion channel gene expression
- A soluble cytosolic protein that binds ions
Correct Answer: A membrane protein that allows passive ion flow across the membrane when gated
Q2. Which statement best distinguishes ligand-gated from voltage-gated ion channels?
- Ligand-gated channels open in response to chemical binding; voltage-gated channels open in response to changes in membrane potential
- Ligand-gated channels require ATP; voltage-gated channels do not
- Ligand-gated channels transport ions actively; voltage-gated channels transport ions passively
- Ligand-gated channels are only in the heart; voltage-gated channels are only in neurons
Correct Answer: Ligand-gated channels open in response to chemical binding; voltage-gated channels open in response to changes in membrane potential
Q3. Which receptor is a classic example of a Cys-loop ligand-gated ion channel?
- Nicotinic acetylcholine receptor
- Voltage-gated sodium channel
- NMDA receptor
- CFTR chloride channel
Correct Answer: Nicotinic acetylcholine receptor
Q4. GABA-A receptors primarily increase membrane permeability to which ion?
- Chloride (Cl-)
- Sodium (Na+)
- Potassium (K+)
- Calcium (Ca2+)
Correct Answer: Chloride (Cl-)
Q5. Voltage-gated sodium channels are crucial for which phase of the neuronal action potential?
- Rapid depolarization (upstroke)
- Afterhyperpolarization
- Resting membrane potential maintenance
- Repolarization mediated by K+ efflux
Correct Answer: Rapid depolarization (upstroke)
Q6. Patch-clamp technique principally measures which property of ion channels?
- Single-channel currents and conductance
- mRNA expression of channel subunits
- Whole-cell protein synthesis rates
- Membrane lipid composition
Correct Answer: Single-channel currents and conductance
Q7. What does ion selectivity of a channel mainly depend on?
- The structure of the pore and selectivity filter
- The concentration of cytosolic ATP
- The extracellular matrix proteins
- The lipid composition of the inner nuclear membrane
Correct Answer: The structure of the pore and selectivity filter
Q8. Which toxin is a well-known blocker of voltage-gated sodium channels used experimentally?
- Tetrodotoxin (TTX)
- Ricin
- Streptomycin
- Insulin
Correct Answer: Tetrodotoxin (TTX)
Q9. Benzodiazepines modulate which ion channel receptor class?
- GABA-A receptors as positive allosteric modulators
- Nicotinic receptors as direct agonists
- Voltage-gated calcium channels as pore blockers
- NMDA receptors as competitive antagonists
Correct Answer: GABA-A receptors as positive allosteric modulators
Q10. Which ion channel is the primary target of local anesthetics like lidocaine?
- Voltage-gated sodium channels
- GABA-B receptors
- CFTR chloride channels
- Nicotinic acetylcholine receptors at NMJs
Correct Answer: Voltage-gated sodium channels
Q11. Desensitization of a ligand-gated ion channel refers to:
- A reversible decrease in response despite continued presence of agonist
- Permanent inactivation after a single agonist exposure
- Increase in open probability with prolonged agonist
- Conversion to an ion pump that consumes ATP
Correct Answer: A reversible decrease in response despite continued presence of agonist
Q12. NMDA receptors require which of the following for full activation?
- Glutamate and co-agonist glycine, and relief of Mg2+ block by depolarization
- Only acetylcholine binding
- High extracellular ATP levels
- Phosphorylation by PKA alone
Correct Answer: Glutamate and co-agonist glycine, and relief of Mg2+ block by depolarization
Q13. CFTR, the defective channel in cystic fibrosis, is best described as:
- An ATP-gated chloride channel (an ABC transporter family member)
- A voltage-gated potassium channel
- A ligand-gated sodium channel in neurons
- A proton pump in lysosomes
Correct Answer: An ATP-gated chloride channel (an ABC transporter family member)
Q14. Single-channel conductance is typically expressed in which unit?
- Picosiemens (pS)
- Milligrams (mg)
- Molarity (M)
- Volts (V)
Correct Answer: Picosiemens (pS)
Q15. A use-dependent blocker preferentially binds to which state of an ion channel?
- Open or inactivated states that occur during frequent channel activity
- Closed resting state only
- Latent unfolded protein conformations
- Extracellular matrix-bound channels
Correct Answer: Open or inactivated states that occur during frequent channel activity
Q16. Which potassium channel structural feature is key to high K+ selectivity over Na+?
- The carbonyl-lined selectivity filter that mimics K+ hydration shell
- A wide nonselective pore that excludes all cations
- An ATP-binding domain inside the pore
- Ligand-binding domain on the extracellular loop
Correct Answer: The carbonyl-lined selectivity filter that mimics K+ hydration shell
Q17. Which class of drugs is primarily used as calcium channel blockers in cardiovascular therapy?
- Dihydropyridines (e.g., amlodipine)
- Benzodiazepines
- SSRIs
- Beta-lactam antibiotics
Correct Answer: Dihydropyridines (e.g., amlodipine)
Q18. Positive allosteric modulators of an ion channel:
- Enhance channel response to agonist without directly activating the channel alone
- Block the ion conduction pore irreversibly
- Act as competitive antagonists at the agonist binding site
- Decrease open probability and reduce current
Correct Answer: Enhance channel response to agonist without directly activating the channel alone
Q19. Which experimental assay is commonly used in high-throughput screening for ion channel modulators?
- Membrane potential-sensitive fluorescent dye assay
- Western blot for channel proteins
- ELISA for channel ligands
- Mass spectrometry of lipids
Correct Answer: Membrane potential-sensitive fluorescent dye assay
Q20. The reversal potential for a single ion channel is predicted by:
- The Nernst equation for that ion
- The Michaelis-Menten equation
- Henderson-Hasselbalch equation
- Beer-Lambert law
Correct Answer: The Nernst equation for that ion
Q21. Which drug is a noncompetitive NMDA receptor antagonist used clinically for anesthesia and depression?
- Ketamine
- Diazepam
- Lidocaine
- Amlodipine
Correct Answer: Ketamine
Q22. Phosphorylation of ion channel subunits commonly affects:
- Channel gating kinetics, trafficking and surface expression
- The DNA sequence of the channel gene
- The ion valence in the extracellular fluid
- Irreversible proteolytic cleavage of the channel pore
Correct Answer: Channel gating kinetics, trafficking and surface expression
Q23. Which receptor family includes nicotinic ACh, GABA-A, glycine and 5-HT3 receptors?
- Cys-loop ligand-gated ion channel family
- ABC transporter family
- TRP channel family
- Voltage-gated potassium channel family
Correct Answer: Cys-loop ligand-gated ion channel family
Q24. Which statement is true about ion channels versus transporters?
- Ion channels allow rapid passive flow; transporters move solutes more slowly, often with conformational changes
- Ion channels require ATP to open; transporters do not
- Transporters are exclusively located in mitochondria; channels are only in plasma membrane
- Channels cannot be regulated by drugs while transporters can
Correct Answer: Ion channels allow rapid passive flow; transporters move solutes more slowly, often with conformational changes
Q25. Channelopathies are best described as:
- Diseases caused by dysfunctional ion channels due to genetic or acquired defects
- Infections of ion channels by bacteria
- Autoimmune destruction of membrane lipids
- Excessive production of ion channel proteins with no functional consequence
Correct Answer: Diseases caused by dysfunctional ion channels due to genetic or acquired defects
Q26. Which ion channel property does open probability (Po) represent?
- The fraction of time a channel spends in the open state
- The number of ions that bind to the channel per second
- The total number of channel proteins synthesized per cell
- The voltage required to inactivate the channel permanently
Correct Answer: The fraction of time a channel spends in the open state
Q27. Which ion blocks NMDA receptors at resting membrane potentials?
- Magnesium (Mg2+)
- Calcium (Ca2+)
- Chloride (Cl-)
- Sodium (Na+)
Correct Answer: Magnesium (Mg2+)
Q28. Which mechanism best describes how class I antiarrhythmic drugs (e.g., flecainide) act on Na+ channels?
- Use-dependent block by binding to open/inactivated Na+ channels
- Activating Na+ channel transcription to increase current
- Enhancing Na+/K+ ATPase activity indirectly
- Blocking extracellular Mg2+ binding sites
Correct Answer: Use-dependent block by binding to open/inactivated Na+ channels
Q29. Which feature is measured to determine single-channel kinetics experimentally?
- Open and closed dwell-time distributions from patch-clamp recordings
- Whole-organism behavioral changes only
- mRNA half-life of channel transcripts
- Total membrane cholesterol content
Correct Answer: Open and closed dwell-time distributions from patch-clamp recordings
Q30. In drug design, targeting ion channel auxiliary subunits can:
- Modify channel trafficking, gating and pharmacology to achieve subtype-selective effects
- Completely eliminate all channel functions in the body
- Convert ion channels into enzymes
- Only affect gene transcription but not channel function
Correct Answer: Modify channel trafficking, gating and pharmacology to achieve subtype-selective effects
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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