Cell Signalling and Receptor Mechanisms · USMLE Step 1

A receptor that directly opens an ion channel in response to ligand binding is best classified as:

  1. G-protein–coupled receptor (metabotropic type)
  2. Enzyme-linked (catalytic) receptor
  3. Ligand-gated ion channel receptor
  4. Intracellular nuclear hormone receptor
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Correct answer: Ligand-gated ion channel receptor

Ligand-gated ion channels (ionotropic receptors) open in response to ligand binding, allowing ions to pass through the membrane; they are distinct from GPCRs and enzyme-linked receptors.

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