Which event is directly mediated by a ligand-gated ion channel?

• A. Activation of G-proteins leading to second messenger production
• B. Rapid influx of ions across the plasma membrane upon ligand binding
• C. Phosphorylation of tyrosine residues on intracellular proteins
• D. Translocation of steroid hormone receptors to the nucleus

Answer: (B)

Verified step by step guidance

1. Understand the function of ligand-gated ion channels: These are transmembrane proteins that open to allow ions to pass through the plasma membrane in response to the binding of a specific ligand (e.g., neurotransmitter).
2. Identify the key feature of ligand-gated ion channels: They mediate the rapid influx or efflux of ions (such as Na⁺, K⁺, Ca²⁺, or Cl⁻) across the plasma membrane, which occurs almost immediately upon ligand binding.
3. Eliminate options that do not involve ion movement: For example, activation of G-proteins and second messenger production is mediated by G-protein-coupled receptors, not ligand-gated ion channels. Similarly, phosphorylation of tyrosine residues is associated with receptor tyrosine kinases, and translocation of steroid hormone receptors involves intracellular receptors, not ion channels.
4. Focus on the correct event: The rapid influx of ions across the plasma membrane upon ligand binding is the hallmark of ligand-gated ion channel activity.
5. Conclude that the correct answer is the event directly mediated by ligand-gated ion channels, which is the rapid influx of ions across the plasma membrane upon ligand binding.