Cardiac Ion Channels (Exam IV)

Question 1

What does the i stand for in describing ion channels?

Answer 1

i = current

Question 2

What is the i_KI channel?
What is its gating mechanism?
What three things define its purpose?

Answer 2

• 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

Question 3

What is the i_Na channel?
What is this channel’s gating mechanism?
What phase is this channel open?
What does inactivation of this channel contribute to?

Answer 3

• Fast Na⁺ Channel
• Voltage-Gated
• Phase 0
• Inactivation contributes to phase I.

Question 4

What is the i_TO channel?
What is this channel’s gating mechanism?
When does this gate open & what phase of the cardiac action potential does it contribute towards?

Answer 4

• K⁺ Transient Outward channel
• Voltage-Gated
• Opens at very end of Phase 0 thus contributing to Phase 1.

Question 5

What is the i_Ca channel?
What is this channel’s gating mechanism?
When does this channel open & close?

Answer 5

• L-type Ca⁺⁺ Channel
• VG & Ligand
• Opening causes phase 2, closing contributes to phase 3

Question 6

Which channels are enhanced by β-adrenergic & sympathetic stimulation?

Answer 6

• i_Ca channel
• i_f channel

Question 7

What is the i_K channel?
What is this channel’s gating mechanism?
What does this channel contribute to the cardiac action potential?
What enhances this channel’s function?

Answer 7

• K⁺ Delayed Rectifier Channel
• Voltage-Gated
• Phase 3 enhancement
• ↑ Intracellular Ca⁺⁺

Question 8

What is the i_KATP channel?
What is this channel’s gating mechanism?
When does this channel open? Why?

Answer 8

• K⁺ ATP sensitive channel
• Ligand Gated (ATP)
• Opens in response to ↓ ATP = ↑pK⁺ = - Vᵣₘ.
• Protective mechanism for myocardial ischemia.

Question 9

What is the i_KACh channel?
What is this channel’s gating mechanism?
What three effects are achieved by activation of this channel?

Answer 9

• K⁺ ACh-activated channel
• Ligand-gated
  1. Shortens Phase 2
  2. ↓ Diastolic Depolarization (thus ↓ HR)
  3. Hyperpolarizes Vᵣₘ

Question 10

What is the i_f channel?
Why the “f”?
What is this channel’s gating mechanism?

Answer 10

• HCN (Hyperpolarization Cyclic Nucleotide channel)
• “f” is for funny; funny because it opens in response to hyperpolarization.
• Voltage-Gated & Ligand-Gated

Question 11

What ions conduct through the i_f channel?
What enhances this channel’s activity?
What suppresses this channel’s activity?

Answer 11

• Na⁺ (primary), K⁺, Ca⁺⁺
• β-agonism = enhancement
• Vagal (PSNS) activity = inhibition