Learning Objective

By the end of this note, the learner should be able to: Identify drugs that act on ligand-gated ion channels and differentiate them from GPCR-mediated mechanisms.

Certain membrane receptors are ligand-gated ion channels (LGICs), meaning they directly open ion channels without involving second messengers. When an agonist binds, the receptor itself forms or opens an ion channel, allowing rapid ion flux across excitable membranes.

Nicotinic Acetylcholine Receptor (nAChR) – Na⁺/K⁺ Ion Channel

• Found in autonomic ganglia, neuromuscular junction (NMJ), and CNS.
• Activated by acetylcholine and nicotine.
• Target for:
  • Nicotine
  • Choline esters (some activate nicotinic receptors)
  • Ganglion blockers
  • Neuromuscular blockers (e.g., succinylcholine)

GABA-Α​ Receptor – Cl⁻ Ion Channel

• Major inhibitory receptor in the CNS.
• Binding increases chloride influx → hyperpolarization.
• Modulated by:
  • Benzodiazepines
  • Barbiturates
  • Some anticonvulsants

Drugs acting on them include nicotine, choline esters, ganglion blockers, neuromuscular blockers, benzodiazepines, and barbiturates.

Activity