Cardiac Ion Channels (Exam IV) Flashcards
What does the i stand for in describing ion channels?
i = current
What is the iKI channel?
What is its gating mechanism?
What three things define its purpose?
- K⁺ (Inward Rectifying Channel)
- Voltage-Gated
Purpose:
1. ↑ pK⁺ during Phase 4
2. Phase 0-2 closure = ↑ plateau & preserved K⁺
3. Contributes to diastolic depolarization
What is the iNa channel?
What is this channel’s gating mechanism?
What phase is this channel open?
What does inactivation of this channel contribute to?
- Fast Na⁺ Channel
- Voltage-Gated
- Phase 0
- Inactivation contributes to phase I.
What is the iTO channel?
What is this channel’s gating mechanism?
When does this gate open & what phase of the cardiac action potential does it contribute towards?
- K⁺ Transient Outward channel
- Voltage-Gated
- Opens at very end of Phase 0 thus contributing to Phase 1.
What is the iCa channel?
What is this channel’s gating mechanism?
When does this channel open & close?
- L-type Ca⁺⁺ Channel
- VG & Ligand
- Opening causes phase 2, closing contributes to phase 3
Which channels are enhanced by β-adrenergic & sympathetic stimulation?
- iCa channel
- if channel
What is the iK channel?
What is this channel’s gating mechanism?
What does this channel contribute to the cardiac action potential?
What enhances this channel’s function?
- K⁺ Delayed Rectifier Channel
- Voltage-Gated
- Phase 3 enhancement
- ↑ Intracellular Ca⁺⁺
What is the iKATP channel?
What is this channel’s gating mechanism?
When does this channel open? Why?
- K⁺ ATP sensitive channel
- Ligand Gated (ATP)
- Opens in response to ↓ ATP = ↑pK⁺ = - Vᵣₘ.
- Protective mechanism for myocardial ischemia.
What is the iKACh channel?
What is this channel’s gating mechanism?
What three effects are achieved by activation of this channel?
- K⁺ ACh-activated channel
- Ligand-gated
1. Shortens Phase 2
2. ↓ Diastolic Depolarization (thus ↓ HR)
3. Hyperpolarizes Vᵣₘ
What is the if channel?
Why the “f”?
What is this channel’s gating mechanism?
- HCN (Hyperpolarization Cyclic Nucleotide channel)
- “f” is for funny; funny because it opens in response to hyperpolarization.
- Voltage-Gated & Ligand-Gated
What ions conduct through the if channel?
What enhances this channel’s activity?
What suppresses this channel’s activity?
- Na⁺ (primary), K⁺, Ca⁺⁺
- β-agonism = enhancement
- Vagal (PSNS) activity = inhibition