The myogenic response (Bayliss effect) in arterioles allows autoregulation of blood flow. The mechanism involves stretch-activated channels and leads to membrane depolarization and vasoconstriction. Which channels are primarily responsible for the initial depolarizing current in vascular smooth muscle during myogenic activation?
- A Mechanosensitive cation channels (TRP channels, particularly TRPC6 and TRPM4) that depolarize the membrane, followed by L-type Ca²⁺ channel activation ✓
- B L-type voltage-gated Ca²⁺ channels activated by initial mechanical stimuli
- C Na⁺/Ca²⁺ exchanger operating in reverse mode during stretch
- D Inwardly-rectifying K⁺ (Kir2.1) channels that depolarize on stretch
Correct answer: A. Mechanosensitive cation channels (TRP channels, particularly TRPC6 and TRPM4) that depolarize the membrane, followed by L-type Ca²⁺ channel activation
Explanation
The myogenic response is initiated when mechanosensitive non-selective cation channels — particularly TRP channels (TRPC6 for direct stretch, TRPM4 for amplification) — open in response to increased intravascular pressure/wall tension. This non-selective cation influx depolarizes the smooth muscle membrane, activating L-type voltage-gated Ca²⁺ channels and causing Ca²⁺-induced vasoconstriction. L-type channels are essential for the contraction but are not the initial mechanosensors. Kir channels, when opened, would hyperpolarize (vasodilation), not depolarize.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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