The hypoxic ventilatory response is primarily mediated by peripheral chemoreceptors in the carotid bodies. These chemoreceptors detect low PO₂ via which cellular mechanism in type I (glomus) cells?
- A Hypoxia inhibits O₂-sensitive K⁺ channels, causing depolarisation and Ca²⁺-dependent dopamine/ATP release ✓
- B Hypoxia activates HIF-1α to upregulate VEGF, increasing neural sensitivity
- C Hypoxia is sensed by cytochrome b558 (NADPH oxidase), generating H₂O₂ that opens Cl⁻ channels
- D Peripheral chemoreceptors respond to PO₂ below 60 mmHg by decreasing cytoplasmic ATP/ADP ratio which activates KATP channels
Correct answer: A. Hypoxia inhibits O₂-sensitive K⁺ channels, causing depolarisation and Ca²⁺-dependent dopamine/ATP release
Explanation
Type I glomus cells contain O₂-sensitive K⁺ channels (including TASK and BKCa channels). Hypoxia inhibits these channels, causing membrane depolarisation, voltage-gated Ca²⁺ channel opening, and Ca²⁺-triggered exocytosis of neurotransmitters (primarily dopamine and ATP). These activate afferent fibres of the carotid sinus nerve (CN IX) to the respiratory centres. The carotid bodies respond steeply to PO₂ below 60 mmHg (the shoulder of the O₂-Hb dissociation curve). Central chemoreceptors in the medulla respond to CO₂/pH, not hypoxia directly.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.