Cromolyn sodium (sodium cromoglicate) prevents mast cell degranulation by which precise mechanism?
- A Blocks histamine H1 receptors on mast cells, preventing autocrine positive feedback stimulation
- B Competitively antagonises IgE binding to FcεRI receptors on mast cells
- C Inhibits phospholipase C, reducing IP3-mediated calcium release from ER stores
- D Inhibits chloride channel opening (specifically TMEM16A/anoctamin-1) in mast cells, preventing hyperpolarisation-dependent calcium influx required for degranulation ✓
Explanation
Cromolyn stabilises mast cells by blocking the opening of calcium-sensitive chloride channels (thought to involve TMEM16A and related channels) triggered by antigen-IgE-FcεRI cross-linking. Normally, membrane depolarisation following chloride channel opening triggers voltage-operated calcium entry, which drives phospholipase activation and exocytosis of granules. Cromolyn disrupts this early channel-mediated step, preventing calcium influx and downstream degranulation. Cromolyn does NOT block H1 receptors, does not compete with IgE (unlike omalizumab), and does not inhibit PLC directly. It must be used prophylactically before allergen exposure.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.