Cell Signalling and Receptor Mechanisms · USMLE Step 1

Which of these receptor mechanisms typically results in the fastest cellular response (milliseconds)?

  1. GPCR signaling via cAMP
  2. RTK-mediated kinase cascade
  3. Ligand-gated ion channel opening
  4. Nuclear receptor–mediated gene transcription
Show answer and explanation

Correct answer: Ligand-gated ion channel opening

Ligand-gated ion channels open almost immediately upon ligand binding, allowing ion flux that leads to rapid responses — much faster than second messenger or transcription-mediated pathways.

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