In the hypoxic ventilatory response (HVR), peripheral chemoreceptors (carotid bodies) are the primary sensors. The carotid body glomus type I cells respond to hypoxaemia by:

• A Hyperpolarisation activating voltage-gated Na+ channels
• B Direct glutamate release activating carotid sinus nerve without depolarisation
• C Inhibition of O2-sensitive K+ channels causing depolarisation and Ca2+-mediated dopamine release ✓
• D cAMP-mediated signalling independently of membrane potential changes

Explanation

Carotid body glomus (type I) cells express O2-sensitive K+ channels (TASK and TREK family). Hypoxia inhibits these channels, causing cell depolarisation. The resulting membrane depolarisation activates voltage-gated Ca2+ channels; Ca2+ influx triggers vesicular release of dopamine, ATP, and acetylcholine onto the afferent carotid sinus nerve (Hering's nerve, CN IX branch). This signal reaches the nucleus tractus solitarius, increasing respiratory drive. The response is immediate (seconds) and crucial for hypoxic ventilatory response.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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