In cardiac electrophysiology, which ion channel opening is predominantly responsible for the rapid Phase 0 depolarization spike in ventricular myocyte action potentials?
Answer and explanation
Correct answer: D. Voltage-gated fast channels
- Step 1: Differentiate ventricular myocyte (non-pacemaker) action potentials from nodal pacemaker action potentials: ventricular myocytes have a resting potential of maintained by inward rectifying channels ().
- Step 2: Once threshold is reached, voltage-gated fast channels rapidly open, allowing a massive inward current that drives rapid Phase 0 depolarization. In contrast, pacemaker cells (SA and AV nodes) lack fast channels and rely on slower L-type channels for Phase 0.
Answer
Voltage-gated fast channels.
Why not the others: L-type voltage-gated channels are responsible for Phase 0 in pacemaker nodal tissue and the Phase 2 plateau in ventricular myocytes; Inward rectifying channels maintain the negative resting membrane potential during Phase 4; Funny () mixed channels drive spontaneous Phase 4 slow diastolic depolarization in pacemaker tissue.
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